[Engels] What Are Good Sources of Protein?

**gleke** · 23-10-2012, 19:53

What Are Good Sources of Protein? – Introduction
In recent years, thanks to emerging research, diet books and popular articles, the general public is starting to become aware of something that many athletes (especially bodybuilders) have been saying for a while: higher protein diets are better for weight/fat loss and improved health. In addition, athletes have long been on the search for nutrients or foods that can improve their performance or their adaptation to the training they put themselves through.
Between those two groups, a question that often comes up is “What are good sources of protein?”
Many websites offer simple answers to that question, generally revolving around whatever protein they happen to sell; the answer, as always, is far more complicated than that. A large number of variables go into the declaration of what a good source of protein is and, as always, what is good in one context may not be good in another.
That is to say, the decision over what a good source of protein happens to be is entirely context dependent.
So, in my usual way, I’m going to dissect the question and look at all of the factors that go into determining what constitutes a good source of protein. In this first part of this article series, I’m simply going to introduce and define some terms, I’ll look at each in detail in forthcoming parts of this series (over the next few days).
Before continuing, I’d mention that this topic was of sufficient interest to me that I wrote an entire book on the topic, The Protein Book. Much of what I’ll be presenting will be excerpted from that project.
I’d also note before continuing that there is still a lot of very outdated information about the ‘dangers’ of high-protein diets. I address them in detail in the article Protein Controversies, on this site. And with that out of the way, let me start answering the question “What are good sources of protein?”
The topics I’m going to discuss in each of the following articles, relating to what makes a protein source good (or bad, or middling) are the following:
Digestibility: Before a protein can be used by the body, it has to be digested and absorbed into the bloodstream for use by the body. Proteins vary in their digestibility and, logically, a protein that is poorly digested will be a poor source simply because less of what’s being eaten is being made available to the body. A topic related to digestibility is the speed of digestion and there has been interest since about the late 90′s in how a given protein’s digestion speed affects how it is used by the body.
Protein Quality: In one sense, the topic of protein quality could be used as an overall look at many of the other topics I’m going to discuss. In general, protein quality is a measure of how well or poorly a given protein is used by the body. I’d note that how you define the word ‘use’ here depends also on context. Are we talking about a protein’s ability to sustain life, build muscle, improve performance, improve health? Some measures of protein quality take into account digestion while others do not (which is why I’ll discuss digestion separately), the amino acid profile of the protein tends to be one of the biggest determinants of quality.
Amino Acid Profile: Again, tying in with the issue of protein quality, there is the issue of the amino acid profile of a given protein. For background, amino acids are simply the building blocks of protein, and there are 18-22 distinct amino acids depending on who you talk to (not all sources recognize all of the amino acids). Each one is found in differing proportions in different food protein sources and, under certain circumstances, that profile will affect how it is used in the body or how it functions.
Presence or Absence of Other Nutrients: While often ignored, the presence or absence of other nutrients in a given protein source also impacts on how good of a protein it may be. For example, some protein sources contain high levels of iron, B12 and zinc while others do not; the presence of absence of the omega-3 fatty acids (fish oils) may also be relevant. Calcium is also a consideration.
Other Factors: There are a number of other potential factors surrounding protein that might determine which is a good or bad source under a given context. For example, proteins may show different effects on appetite, or blood sugar control, or what have you. There is also the issue of cost and availability along with the amount of protein in a given amount of whole food proteins. I’ll cover those as a catch-all final category in this series before summing up and looking at a variety of whole food proteins and how they rank on each category.
So those are the major topics I’m going to cover in this series of articles. While it will take a bit of time to cover all of the information I want to cover, by the end of the series you’ll know the answer to the question “What are good sources of protein?“
What Are Good Sources of Protein? – Digestibility
In the introduction to this series of articles, I briefly described a number of different aspects of dietary protein that go into answering the question what is a good source of protein. I’d mention again that ‘good’ in this sense can only be defined in a context-specific way. The protein that might be a good source under one set of conditions may not be a good source under another. That will make more sense as I go through the series.
Today I want to talk about the issue of protein digestibility; to keep the length down I’ll save speed of digestion for Part 3 of the series. Once again I’ll note that much of what will appear in this and subsequent articles in this series is being excerpted or paraphrased from The Protein Book, my complete look at the issue of dietary protein.
One final note: While The Protein Book is fully referenced, with over 500 research studies cited, I will not be citing references on this series of articles unless absolutely absolutely necessary.
A Primer on Protein Digestion
While the breakdown of protein begins in the mouth through the mechanical act of chewing, almost no actual digestion occurs there. Rather, chewed protein hits the stomach where digestion and breakdown occurs via hydrochloric acid and the enzyme pepsinogen.
The majority of protein digestion occurs in the small intestine where protein is broken down into smaller and smaller amino acid (AA, the building blocks of protein) chains via a variety of protein digesting enzymes. You can think of proteins as being a long chain of the AAs, the enzymes basically act like scissors, cutting the chains into smaller and smaller bits.
Prior to absorption into the bloodstream, whole proteins have been broken down to provide single AAs along with two and three AA chains (called di- and tri-peptides); further breakdown occurs in the intestinal cells themselves, finally releasing individual amino acids into the bloodstream.
Generally speaking, AA chains larger than three in length will not be absorbed to any appreciable degree. I’d note that occasionally very small amounts of longer amino acid chains can slip through and this is especially the case in situations like leaky gut syndrome where the normal functioning of the gut has been compromised.
This is actually a very bad thing as the body tends to launch immune/allergic responses to the presence of undigested protein in the bloodstream; which is a big part of why the gut is set up to not allow larger protein chains into the bloodstream under normal circumstances.
Related to this is a recurrent idea, usually in sports nutrition, of supplements containing protein based hormones such as Growth Hormone (GH), Insulin-Like Growth Factor 1 (IGF-1) or others being orally consumed. This can’t work due to the way human digestion of protein works, such peptide hormones will simply be digested in the gut and lose their biological availability.
Let me put this a different way: major pharmaceutical companies have been trying to make an oral insulin (another protein based hormone) for diabetic treatment and have basically given up on it; it took weirdly functioning drugs and there were huge problems with implementation. If the big drug companies haven’t figured out how to do it, neither has the protein powder company claiming it in their ads.
So What is Digestibility?
Now, the above makes it sound like all ingested protein gets into the bloodstream after digestion but this is far from the case. No process in the human body works at 100% efficiency and this is one of them. For various reasons, a proportion of all ingested nutrients will escape digestion, continuing through the intestine to eventually end up in your poop. Fat is typically absorbed with up to 97% efficiency and carbs can vary quite a bit depending on what you’re talking about. But what about protein?
Researchers define protein digestibility as the amount of protein absorbed into the body relative to the amount that was consumed. A quick note: researchers are actually measuring nitrogen absorption and excretion, rather than protein or amino acids per se, but I don’t want to get into the technical details of that here.
So, for example, they might feed someone 50 grams of protein and then see how much comes out the other end. Let’s say that 5 grams of protein show up in the poop. That means that 45 grams of the 50 grams ingested were actually absorbed and that protein would have a digestibility of 90% (45 grams absorbed/50 grams ingested = 0.90 * 100 = 90%).
If 50 grams of protein were fed and 25 grams showed up in the poop, that protein would have a digestibility of only 50% (25 grams absorbed/50 grams ingested = 0.50 * 100 = 50%). Get it?
I want to note that a lot of very silly claims are often made about protein digestibility. Companies selling protein powders argue that the digestibility of their product is impossibly high, vegetarians usually ignore the research on this topic to claim that vegetarian proteins have higher digestibility than animal source proteins, on and on it goes. The research on this is extremely clear and I’ve reproduced the chart from The Protein Book on the digestibility of common foods below.
Food Source

Protein Digestibility (%)
Egg

97
Milk and Cheese

97
Mixed US Diet

96
Peanut Butter

95
Meat and Fish

94
Whole Wheat

86
Oatmeal

86
Soybeans

78
Rice

76
Source: National Research Council. Recommended Dietary Allowances, 10th ed. National Academy Press, 1989.

Looking at the chart above, two major things stand out. The first is that, contrary to the occasional vegetarian claim, vegetable source proteins have a significantly lower digestibility than animal source proteins.

This actually has relevance for an issue beyond the scope of this article: protein requirements. Because they provide less available protein from consumption, a larger amount of vegetable proteins have to be consumed to meet human (or athletic) requirements.
The second is that commonly available animal-source food source proteins have extremely high digestibilities, 94-97%. This means that for every 100 grams of protein consumed, 94-97 grams are being digested and assimilated by the gut.
Given that this likely represents the very high end of digestibility for humans (no process in humans is ever 100%). The odds of a given commercial product being significantly above this is unlikely. As well, even if it were the overall real-world impact would be small.
That is, let’s say a given over-priced commercial protein powder achieved a true 99% digestibility. For every 100 grams consumed, you absorb 99 grams of protein. That’s only 2-5 more grams than a much cheaper whole-food protein. And given that you’ll likely be paying 2-3 times as much for the ‘magic protein powder’, this seems a pretty silly path to pursue.
Which isn’t to say that the protein powder might not have other advantages in a certain circumstance. For example, perhaps the protein powder digests more quickly than the food; this might be valuable under certain circumstances (or negative in others). Which is as good a bridge as I can give to the topic I’m going to discuss in Part 3 of this series: Digestion Speed.
What Are Good Sources of Protein? – Speed of Digestion Part 1
In the last article, What are good sources of protein – Digestibility, I examined some basics of protein digestibility and presented data on the gross digestibility of varying proteins. Summing up, animal source proteins such as meat, milk and eggs show extremely high (90%+) digestion while vegetable source proteins show much lower values.
However, the efficiency of digestion alone is not the only factor which goes into answering the question What are good sources of protein?
Recently (and by that I mean the late 90′s or so), an interest in the speed of digestion and how that impacts on various aspects of human physiology has occurred. It’s turning out that proteins can digest at fairly different rates and this turns out to affect various physiological processes; the main two are protein synthesis and protein breakdown. As with the last article, I’m going to talk about these terms in brief before moving onto the main thrust of today’s article.
Because I have a lot of information to cover, I’m going to break the topic down into two parts. In Part 1 today, I need to cover a bit more background physiology and talk about the original study that kicked off the entire interest in speed of digestion. In Part 2 (tomorrow), I’ll finish up with some other recent developments. As always, all of this information can be found in a more detailed and expanded fashion in The Protein Book.

Protein Turnover: The Combination of Protein Synthesis and Protein Breakdown
Early ideas about the body held that the different tissues such as fat cells and skeletal muscle (see What Does Body Composition Mean for a little more detail) were essentially static and unchanging. This turns out to be incorrect. At any given time in the body, pretty much all of the cells in your body are undergoing a constant process of breakdown (where larger structures are broken down into smaller) and synthesis (where smaller structures are combined to make larger).
So as you sit here reading this, your fat cells are both breaking down and re-synthesizing the triglyceride (fat) stored in them. Bone is undergoing the same constant processes as well. Of course, the same holds for protein tissues.
Right this moment, your liver is breaking down and remaking various proteins, and your skeletal muscle is in a constant source of breakdown and re-synthesis. While this is actually energetically very costly, and seems wasteful, it turns out to give the human body an incredible adaptability and ability to deal with stress.
The combination of breakdown and re-synthesis is referred to, generally, as turnover. In the context of protein based tissues, this is referred to as protein turnover.
I should note that different tissues in the body break down at drastically different rates. So while liver proteins may break down and be completely re-synthesized in a number of hours, skeletal muscle is turning over more slowly. Tissues such as organs, tendons and ligaments turn over much more slowly. As you’ll see, this actually has some implications for what I’m going to talk about in just a moment.
What happens overall to a given tissue (e.g. whether it grows, shrinks or stays the same) depends on the relative rate of synthesis and breakdown. Simply:
§ If synthesis is greater than breakdown, there will be an increase in the amount of that tissue.
§ If breakdown is greater than synthesis, there will be a decrease in the amount of that tissue.
§ If breakdown equals synthesis, there will be no change in the amount of that tissue.
This also means that, fundamentally, we have two different ways to have an impact on the amount of a given tissue. Let’s say for example that someone wants to increase the amount of muscle that they have. They can either try to increase protein synthesis, decrease protein breakdown, or cause both to occur.
This is an important distinction because various things (such as nutrients, training, drugs) can differentially affect each process. As you’ll see in just a second, speed of digestion is one of those things and the rate of digestion of a given protein can affect protein synthesis vs. breakdown differently.

The Now Infamous Boirie Study
Back in 1997, a research group in France published the first paper on the topic of slow and fast proteins. Titled, “Slow and fast dietary proteins differently modulate postprandial protein accretion.”, this is the paper that kicked off the entire field of fast and slow proteins.
In that paper, subjects were fed either casein or whey, the two proteins found in milk (see Milk: The New Sports Drink? A Review – Research Review for more information), and blood amino acid level along with whole body protein synthesis and breakdown were measured. I’d note that both proteins were given after a morning fast with no other nutrients (carbohydrates or fat) provided. This is important because the results of this study don’t necessarily hold when other nutrients are being consumed, or someone is consuming a given protein later in the day (when other meals are still digesting).
The researchers found the following: whey spiked blood amino acid levels faster than casein, but blood amino acid levels dropped more quickly as well. Casein, in contrast, took much longer to digest, actually providing amino acids for around 8 hours to the body (you might consider that data point the next time you hear that you have to eat every three hours or your muscles will fall off, a topic I cover in Meal Frequency and Energy Balance).
I actually want to clarify that a bit since there has been a lot of confusion over what the study actually found. Both casein and whey hit the bloodstream at about the same time (about an hour in), that is, whey didn’t actually get into the system faster. However, whey spiked blood amino acid levels higher at that one hour point. Figure 1 (taken from The Protein Book) shows this.

Amino acid profile for casein vs. whey
Note that both proteins enter the bloodstream at about the same time, around the one hour mark. Whey simply spikes blood amino acids faster (before falling back to baseline levels around hour 4). Casein, in contrast raises amino acid levels to a much lower level but they are sustained for hours (in the graphic, at the 7 hour mark, blood amino acid levels were still above where they started).
So it’s not that whey gets into the system faster, it just spikes blood amino acid levels higher at the same time point (about an hour after consumption).
Now, the next bit of this study was an examination of the effects of these proteins on protein synthesis and breakdown. Basically, it was found that whey raised protein synthesis with no effect on protein breakdown while casein decreased protein breakdown without affecting protein synthesis.
Hence, whey become known as an ‘anabolic’ protein (anabolic just means making bigger things out of smaller things) and casein was an ‘anti-catabolic’ protein (catabolic means making smaller things out of bigger things, and anti-catabolic means that casein prevents that).
I’d also note that more of the whey was burned for energy (oxidized) compared to the casein.
This, of course, got taken wildly out of context to sell protein powders. However, note above I said that the research was looking at whole-body protein synthesis and breakdown. It wasn’t examining skeletal muscle per se. It’s just as logical to conclude that the whey stimulated liver protein synthesis as skeletal muscle but, of course, supplement companies don’t ever talk about that.
And with that I’m going to wrap up Part 1. In Part 2 (tune in tomorrow), I’ll talk about more recent research and some implications of speed of digestion for answering the question What are good sources of protein?

**gleke** · 23-10-2012, 19:58

Dubbel.

**gleke** · 23-10-2012, 19:58

Driedubbel..

Ik druk 1 maal op bericht versturen en hij plaats het er 3x op..
Ik zie trouwens dat BN ook moeite heeft met het weergeven van de grafieken en tabellen, hiervoor verwijs ik je naar de bovenstaande site.

**gleke** · 23-10-2012, 19:59

What Are Good Sources of Protein? – Protein Quality
Having finished looked at the issue of speed of digestion in What are good sources of protein – Speed of Digestion Part 3, I want to move onto the next topic that I mentioned in the introduction: protein quality. I’m going to keep this article as brief as possible, for reasons I’ll explain at the end of the article. If you want or need more, you can pick up The Protein Book which has a detailed discussion of the issue.

What Does Protein Quality Mean?
Quoting directly from The Protein Book:
Protein quality refers, in a general sense, to how well or poorly the body will use a given protein. More technically, protein quality refers to how well the essential amino acid (EAA) profile of a protein matches the requirements of the body; the digestibility of the protein and bioavailability of the amino acids (AAs) also play a role (1,2).
Essentially, protein quality simply refers to how well or how poorly a given protein is used by the body once it has been digested. Clearly, any protein that escapes digestion (as discussed in What are good sources of protein? – Digestibility) can’t do anything in the body but that doesn’t mean that all of the protein that is digested automatically works the same in the body.
Repeating myself slightly, protein quality has to do with how well a given dietary protein is used by the body for all of the different purposes that protein is used for. And the quality of the protein has to do with factors such as the amino acid profile of the protein (amino acids are just the building blocks of individual proteins) along with the speed of digestion issue I discussed in the last series of articles. I’ll talk about amino acid profile a little bit in the next article of this series.
Recall, for example, that whey protein, because of its rapid digestion, tends to promote amino acid oxidation (burning); obviously amino acids that are burned for energy can’t be used for things like synthesizing muscle tissue or what have you.
With that said, I want to take a brief look at all of the major methods of scoring protein quality. Again, for a more detailed discussion, please pick up a copy of The Protein Book.
Method of Measuring Protein Quality
Chemical Score:The chemical score of a protein refers simply to its amino acid profile rated to some standard or reference protein, each amino acid is rated on a scale indicating how much of that amino acid is present compared to the reference protein.
For example, let’s say that the reference protein being used contains 100 milligrams of the amino acid leucine. Let’s say that the protein we’re looking at contains only 75 mg of leucine; that protein would be given a chemical score of 75% for leucine; if instead it contained 125 mg of leucine, it would be given a chemical score of 125% for that amino acid.
Frankly, chemical score isn’t used very much anymore and the whole concept is based on knowing what the ideal protein for human health and function actually is. Even in that case, chemical score says nothing about digestion or how a given protein is actually used by the body.
Biological Value(BV): BV is one of the more common methods of measuring protein quality and tends to be the one that is seen the most so I’m going to give it the most discussion. BV is simply a measure of how much of the protein actually entering the bloodstream is retained in the body (e.g. used for proteins synthesis or what have you); that is it takes digestibility into account. I’d note that some of the protein (again, researchers are actually measuring nitrogen going in vs. out but that’s not important here) that gets into the bloodstream comes back out in the urine.
Since BV is comparing protein in vs. out, the highest possible value for BV would be 100, that would mean that 100% of the protein that got into the bloodstream is being used by the body (note again, some protein won’t be digested in the first place). No protein has a BV of 100 and claims that whey have a BV of 140 are simply nonsense (they are based on a misreading of a specific paper); this would suggest that for every gram of protein from whey that is eaten, the body somehow stores 1.4 grams of protein. An impossibility.
BV is measured by feeding subjects a protein free diet for three days and then giving them a measured amount of protein, the amount that comes back out in the urine and poop and skin and such are then estimated and BV is calculated. This type of study is called a nitrogen balance study and, for a variety of reasons can be very inaccurate. Again, more detail can be found in The Protein Book.
I’d note that BV is typically tested at very low protein intakes, far below what the average American (and certainly any athlete would eat). Eating more protein lowers the apparent BV which has led to some humorously bad interpretations of BV. As well overall energy intake drastically affects BV; if you eat more calories, apparent BV goes up, if you eat less, apparent BV goes down.
Because of this, BV has a lot of practical problems. It’s very accurate under conditions of low protein intake but caloric has to be meticulously controlled. At the types of high protein intakes seen in most modern countries, as well as with athletes, BV doesn’t tend to say very much.
Net Protein Utilization (NPU): NPU is extremely similar to BV. But while BV is comparing the amount of protein that is actually digested to the amount that is stored in the body, NPU simply compares the amount of protein eaten to the amount stored in the body. Put differently, BV takes digestion and actual absorption of protein into account; NPU doesn’t. This doesn’t make NPU very useful.
Protein Efficiency Ratio (PER): PER is a measure of the amount of weight gain (in grams) in rats compared to their protein intake. It’s always measured in young growing rats and, frankly, has about zero relevance to human physiology.
Protein Digestibility Corrected Amino Acid Score (PDCAAS): The PDCAAS is the newest method of scoring protein quality and is the one most in common use. Like chemical score it compares the amino acid profile to some reference protein; as well it it takes into account digestion. Somewhat interestingly, proteins that were scored as low quality (such as soy protein) achieved a much higher score via the PDCAAS. This is actually in line with research showing that quality soy proteins work just fine for supporting basic human protein needs.
PDCAAS does have a couple of problems, however. The first is that the highest score possible is set at 1.0, no protein can score above that value regardless of the apparent quality. Basically, scores higher than 1 are simply rounded back down.
Additionally, part of the premise of the PDCAAS is that the ideal pattern of amino acids for supporting human health (or athletic performance) is actually known. It’s possible that the ideal protein for supporting basic human health might change with age (for example, amino acid and protein requirements do change with age) or might be different different types of athletes. The idea that a single amino acid profile can be ideal under all circumstances is tenuous at best.

Does Protein Quality Matter?
Which brings me to my major commentary about the issue of protein quality: I consider it essentially irrelevant. I noted above that BV, for example, is measured at very low levels of protein intake and this tends to hold true for many of the other methods. Protein quality is measured under conditions of low intake because the primary application of protein quality has to do with ensuring adequate nutrition for people who don’t have enough food. Which means that it stops having much relevance at high intakes.
That is to say, small differences in protein quality make an absolutely massive difference if you’re talking about someone in the third world who is eating small amounts of a single source of poor quality protein and doing so in the context of insufficient total caloric intake in the first place.
In that situation, small improvements in protein quality (by adding other foods or even a specific amino acid) may pay massive dividends in terms of improving health or survival of that group. So would feeding them in general. The World Health Organization (WHO) is very concerned with this issue which is why they make a big deal out of protein quality; it’s relevant to the population that they are worried about.
Anybody reading this article isn’t in that situation for the most part. If you have the Internet and time to visit my site, odds are that finding food in general, or protein in specific, to eat today isn’t your major concern. When people are consuming mixed proteins at the levels seen in the general public (typically 2-3 times the RDA level), and especially among athletes (who often eat more than that), protein quality ceases to become an issue. This is especially true when lots of calories are being eaten.
And while it’s possible that specific proteins might be more or less useful for athletic applications (e.g. providing amino acids specifically needed by those athletes), any athlete eating large amounts of protein will generally be consuming plenty of what they need anyhow.
Athletes tend to get really obsessive about the issue (and of course supplement companies pander to that) but at a protein intake of 1-1.5 grams per pound of lean body mass coming from mixed high quality sources, quality just won’t matter. There is much more discussion of this in The Protein Book.
One possible exception to this is dieting; when calories are restricted, the way the body uses protein can change and different proteins may be specifically beneficial (the dairy proteins whey, casein or simply milk are valuable in this regards for reasons outside the scope of this article).
I suppose if someone in the modern world was eating small amounts of a single source of poor quality protein, quality would matter as well. But that would be some weird self-imposed dietary pattern, not the kind that people in many parts of the world follow because that’s all tha is available.
The bottom line is that, for folks in the modern world, eating fairly large amounts of high quality proteins and lots of calories, quality simply isn’t much of an issue in terms of answering the question what are good sources of protein. Outside of a few weird exceptions, noted above, it simply won’t be relevant.
Next time, I’ll discuss an issue related to this one which is the specific amino acid profile of proteins
What Are Good Sources of Protein? – Amino Acid Profile Part 1
Continuing from Wednesday’s article on What are good sources of protein? – Protein Quality, I want to talk a little bit about the amino acid profile of proteins and how that impacts on the answer to the question What are good sources of protein.
I’m going to actually divide this into two parts to keep it from getting too long. In Part 1, I’ll discuss some basic concepts and look at how the amino acid profile of various proteins relates to supporting basic bodily function. In Part 2, which I’ll run on Monday, I’ll discuss the possibility that athletes have specific amino acid requirements above and beyond what’s necessary to support basic function.
What are Amino Acids?
Now, as I’ve mentioned but not gone into any great detail in this series, amino acids are simply the building blocks of protein. Depending on which reference source you use, there are 18-22 different amino acids that occur in the human food supply. Whole food proteins are simply long chains of these amino acids bonded together. Typically whole food proteins are extremely long chains of amino acids, as I discussed in What are good sources of protein? – Digestibility, these long chains are cut into smaller and smaller chunks during digestion until only single amino acids and chains of 2-3 amino acids are actually absorbed.
I’d note that individual amino acids are often sold for either health or sports performance purposes. Readers may be familiar with the amino acid L-tryptophan which is often sold as a sleep aid. L-Tryptophan converts to serotonin in the brain which is involved in sleep. Take L-tryptophan on an empty stomach and you get drowsy because of increased brain serotonin levels.
In the athletic realm, all kinds of products are available. The branched-chain amino acids (BCAA) L-leucine, L-isoleucine and L-valine have been pushed for years to athletes; recently there has been a big push for isolated leucine for a number of reasons that I’ll touch on in Part 2.
Another example is L-carnitine, an amino acid involved in fat metabolism that has been sold as a fat loss aid for years (it doesn’t work by the way). I, myself, have recommended the amino acid L-tyrosine (which converts in the brain to adrenaline and noradrenaline) as part of a stimulant cocktail to improve performance.
You may be wondering what the ‘L-’ means above; it refers to the chemical structure of the amino acid (to be technical, it’s an organic chemistry notation that stands for levorotary). There are also ‘D-’ amino acids (the ‘D’ stands for dextrorotary). The human body only uses the ‘L-’ form of amino acids; the ‘D-’ form can actually be toxic.

Essential vs. Non-essential Amino Acids
I should note that the amino acids are usually subdivided into essential amino acids and inessential or non-essential amino acids. It’s important to note that both are absolutely essential for life, the term inessential/non-essential simply means that those amino acids don’t need to be obtain from the diet; the body can make them. The essential amino acids can only come from the diet; hence they are ‘essential’.y
I should also note things aren’t actually quite this simple, some amino acids which are inessential under normal conditions can become essential under others; glutamine is perhaps the most well known example. Under normal conditions, glutamine is inessential, the body can make what it needs. However, under conditions of massive stress (such as blunt force trauma, burn injuries or sepsis), the body can’t make as much glutamine as it needs; glutamine becomes conditionally essential under those conditions.
And while there are a few other odd exceptions to the essential/inessential distinction, they tend to be rare and not very relevant under most conditions, so I won’t talk about them.

Why do Amino Acids matter?
Now, as mentioned in What are good sources of protein? – Digestibility, after being broken down in the gut and intestine, proteins then appear in the bloodstream as amino acids. These are then used in the body for various processes such as the synthesis of new proteins.
Your heart, liver and many other organs are made of protein, skeletal muscle contains about 20% protein (most of it is actually water), your hair and skin is made of protein, there are numerous enzymes and liver proteins made in your body every day; all are synthesized from incoming amino acids from the diet.
Recall from What are good sources of protein – Speed of Digestion Part 1, that the tissues in the human body are in a constant state of turnover, which is the combination of breakdown and re-synthesis. So skeletal muscle is being broken down and remade, so is hair, skin, etc. Of course, since no process in the body processed with 100% efficiency, some of the broken down amino acids are lost.
That is, fundamentally, the basis for human protein requirements; the amino acids lost in the process of breakdown and re-synthesis have to be replaced from the diet. Otherwise, there will be a gradual loss of protein tissues in the body (as occurs in complete starvation). Lose enough body protein (about 40%) and you die.
Now, since the body is actually using specific amino acids for these various processes, it’s actually a little more accurate to say that the body has specific ‘amino acid requirements’ rather than ‘protein requirements’ per se. I’d note that there is also a general ‘nitrogen requirement’ (that can only be met with dietary protein) but I don’t want to get into that level of detail.
As a final note, I want to mention that the tissues in the human body that use proteins all use them in varying proportions and amounts. That is, the amino acid profile of say, your liver, or a specific enzyme may not be the same as skeletal muscle, hair or bone. Basically, the tissue you’re focusing on will determine what the ideal amino acid profile ‘might be’. I’ll come back to this.

Back to Protein Quality
Now, as I mentioned in What are good sources of protein – Protein Quality, one of the determinations of protein quality has to do with how well or poorly a given protein fulfills the amino acid requirements of the body and the above discussion basically explains why. Every day your body loses some amino acids which have to be replaced. One determinant of a protein’s quality is how well it matches the body’s need for those specific amino acids.
Now, I should mention again that most of the work on protein quality deals with the issue of general health, especially in those people who are not getting sufficient protein, protein from high quality sources, and who aren’t eating much in the first place. That is, the research is aimed at folks in third world countries.
The goal is to find ways of improving overall health and bodily function in people who are starving to death. And the focus is basically on keeping them healthy overall, that is meeting the amino acid requirements of the whole body in terms of keeping the basic stuff functioning well (or at least passably). Issues such as optimizing athletic performance or increasing muscle mass are not the focus.
Not only does this mean it has questionable relevance to those of us lucky enough to live in a modern world where protein and food is generally very available, it also means that it isn’t aimed at athletes or individuals involved in training (which tends to be the group I focus on). It’s conceivable (and, of course, supplement companies pander to this idea) that athletes or individuals in hard training might have specific requirements for amino acids.
That is to say, it’s conceivable that someone involved in a strength/power sport (powerlifting, bodybuilding, etc.) might require a different amino acid profile to support the growth of skeletal muscle; an endurance athlete might conceivably need a specific amino acid profile to support the synthesis of mitochondria (the powerhouse of the cell) or enzymes involved in energy production. This topic is drastically under studied.
But, simply (and of course this is discussed in great detail in The Protein Book), amino acid requirements can be sub-divided into the amino acid requirements needed to support basic health and bodily function (what most research deals with) and the amino acid requirements (if any) to optimize athletic performance.
Meeting Basic Bodily Requirements
Now, for reasons I’m not going to get to, the amino acid requirements for 2-5 year old children are actually used to examine whether or not a specific protein is sufficient. That is, any dietary protein which has an amino acid profile that meets or exceeds the requirements for 2-5 year old children is considered sufficient to support the basic needs of adults.
I’d note that, in keeping with the section on essential/inessential amino acid discussion above, the real focus is on whether or not a given protein can meet the essential amino acid requirements of the body. Assuming sufficient protein is being consumed in the first place, the inessential amino acid profile isn’t that relevant.
And as I show in Table 2 on Page 56 of The Protein Book (which I’m not going to reproduce here), basically all high quality proteins, and this even includes soy protein, can meet the basic amino acid needs of an adult human being. Human milk, cows milk, eggs, beef, whey and soy all contain amino acids far in excess of the requirements for 2-5 year old children; by extension this means that they can readily meet the requirements for adults.
This is in keeping with the discussion of the PDCAAS from What are good sources of protein – Protein Quality showing that proteins such as soy (which were typically thought of as low quality) are more than sufficient to meet adult human essential amino acid requirements. Assuming adequate dietary protein is being eaten in the first place (and this is basically never an issue in the modern world), all proteins easily meet human protein requirements.
Which doesn’t make them all identical or equivalent mind you; there may be reasons (such as the presence or absence of other nutrients such as iron, zinc, or calcium, or the fatty acid profile) to choose one protein over another. But from the standpoint of amino acid profile, there isn’t much of a functional difference between proteins (I’d note, rather tangentially, that recent work has suggested that fish protein per se seems to have benefits on insulin sensitivity, possibily due to the high taurine content).
Which, as noted above, doesn’t really address the issue of athletes and possible differences in requirements. But that will have to wait for Part 2.
What Are Good Sources of Protein? – Amino Acid Profile Part 2
In What are good sources of protein? – Amino Acid Profile Part 1, I examined the issue of amino acid profile, primarily as it relates to general health and wellness. My basic conclusion, based on the research is that basically any high quality protein source (and this is eminently true in the modern world where people get plenty of protein from mixed sources along with lots of total calories) more than adequately meet the amino acid requirements of adult humans.
Today, I want to continue that by looking at some issues specific to athletes and those involved in heavy exercise training. It’s fairly well established that athletes need more protein than sedentary individuals although there is still great argument over just how much is needed.
Two specific amino acids that tend to get focused on by athletes are the branched chain amino acids (BCAAs) and glutamine, I’ll give a quick primer on those before discussing any of the other specific issues.
There are a number of different ways by which by which exercise training might increase protein/amino acids requirements. This includes the use of amino acids for energy directly during exercise, other pathways of interest (see below), and finally the actual adaptation to training. I also want to touch briefly on the issue of dieting.
To keep this from getting too long, I’m only going to discuss energy use and the other pathways today. Since it will be the longest part, on Thursday or Friday, I’ll look at the issue of the actual adaptations to training and how that might impact on specific amino acid requirements; I’ll also look at the issue of glutamine and BCAA supplementation in that regards. I’ll discuss dieting then as well.
Again, I can’t really do these topics full justice in this article, it took me 225 pages to cover it all in The Protein Book and anybody who wants the full discussion (and all of my study references) should pick up that book.

BCAA: A Primer
The branched chain amino acids (BCAA) refer to three individual amino acids, leucine, isoleucine and valine. They are so named because of their branching structure. It’s been known for years that they are treated differently in the body than the other aminos; while other aminos can all be degraded in the liver, BCAA metabolism is fairly specific to skeletal muscle. In a very real sense, BCAA are muscle food. I should note that while BCAA are primarily used in the muscle, they can also be burned there directly for energy.
The BCAA can not be made within the body and must be obtained by the diet. In that context, I’d note that all high quality proteins actually contain quite a bit of BCAA. Proteins such as meat typically contain about 15% BCAA by weight (e.g. 100 grams of protein will provide about 15 grams of BCAA) while dairy proteins such as whey and casein contain more. Some forms of whey contain as much as 25% BCAA by weight (e.g. 100 grams of whey protein will provide 25 grams of BCAA), casein comes in at about 20%.
Quoting from The Protein Book about this:
A typical diet containing high quality protein will provide 15-20 grams of BCAAs for every
100 grams of protein ingested (25); diets containing a significant amount of whey protein
will contain slightly more than this. A 100 kg athlete consuming 3.0 g/kg protein, or 300
grams of protein per day, would be expected to be consuming 45-60 grams of BCAAs per
day; again, this value would be slightly higher if a large amount of whey protein was being
consumed.
This is an important point because the grand majority of studies which have shown benefits from BCAA supplementation have done so without first providing adequate protein in the first place. And as is always the case with such things; nutrients do very different things when they are shoring up a deficiency or inadequacy than when they are not.

Glutamine: A Primer
Glutamine is a non-essential amino acid (e.g. under normal conditions it can be made in sufficient amounts) although under conditions of very high stress (trauma, burn injury), the body may need more. Crafty supplement manufacturers have tried to liken heavy training to that level of stress which is, frankly, absurd.
Glutamine plays a number of roles in the body, early research showed that it could stimulate protein synthesis when added to cell culture. Glutamine is also involved in immune system function, I’ll talk about this further on. Glutamine is also involved in acid-base balance, some have suggested its consumption on a high-protein diet to help buffer acid production. I suggested glutamine for GH release (GH has some fat mobilizing properties) in The Ultimate Diet 2.0.
As it turns out, the body actually synthesizes a lot of glutamine per day, anywhere from 20-60 grams per day. As it also turns out, a lot of this glutamine is being synthesized from other amino acids, including the BCAA.
As noted above, BCAA can be burned in skeletal muscle directly (and this increases when glycogen has been depleted) and this tends to produce ammonia which the body buffers by converting to glutamine to be sent to the liver. Basically, glutamine is used by the body to transport amino from muscle to other places where it can be disposed of; glutamine is also used heavily by the gut, immune system and kidneys.

Exercise and Amino Acid Requirements: Energy Use During exercise
One source of increased protein requirements during exercise has to do with the direct use of amino acids for energy during exercise. Generally speaking this is fairly specific to endurance training where ~5-10% of the total energy requirements of exercise can be from the burning of amino acids. Specifically, the branched chain amino acids, and especially leucine, can be used directly for energy by exercising muscle.
This does suggest that increased BCAA intake during endurance exercise might be beneficial and, to this point, studies have found that the consumption of small amounts (10-12 grams per hour) of rapidly digesting protein with carbohydrate can decrease muscle damage, may improve recovery between bouts and may improve performance. But, for reasons beyond the scope of this article, I strongly feel that a quickly digesting whole protein such as whey is superior to isolated BCAA in this case.
Because of the vast differences in energetics between weight training and endurance training, there typically isn’t a lot of burning of amino acids during resistance training. It’s conceivable that extremely high-volume training, which depletes muscle glycogen could increase BCAA burning but this is unlikely with anything but the most insane training volumes.
Outside of possible effects on immune system function, there’s really not much role for glutamine in terms of energy production during exercise. Consuming adequate carbohydrate (~30-60 grams per hour) with small amounts of protein (e.g. 10-12 grams of whey protein which will provide 3-4 grams of BCAA) will do more to protect immune system function than glutamine could ever do.

Exercise and Amino Acid Requirements: Other Pathways of Interest
Although they haven’t been studied much, there are other potential pathways that use amino acids that contribute to increased protein requirements by athletes. Quoting again from The Protein Book:
In addition to all of the body’s uses of protein described above, there are a number of
processes of extra importance to athletes. This includes the repair and replacement of
damaged proteins, remodeling of the proteins within muscle, bone, tendon and ligaments,
maintenance of optimal functioning of all of the metabolic pathways that use amino acids
(presumably these pathways are up regulated in athletes due to training), supporting lean
body mass gains, supporting immune system function, and possibly others (4).
Each of these pathways, might conceivably all require a different amino acid pattern for optimal functioning. However, this area is woefully understudied so I can’t comment much.
I do want to discuss the immune system issue a little bit; clearly an athlete who is sick isn’t training well and if they aren’t training they certainly aren’t getting better. Protecting immune system function in athletes (and the problems tend to occur with volume more than intensity) is a key aspect of sports nutrition.
The amino acid glutamine is a key amino in terms of immune system function and there was some interest at one point in using glutamine to prevent immune system function; some studies supported that idea, others did not. As it turned out, BCAA turned out to work better; recall from above that BCAA can be converted to glutamine and BCAA turn out to ‘protect’ glutamine status in the body.
Ensuring sufficient BCAA intake may help protect the immune system during periods of high-volume training and at least one study in endurance athletes found that BCAA supplementation even in the context of adequate daily protein did help; given that many endurance athletes don’t consume sufficient protein in the first place, BCAA might play a role. I’d note that simply raising protein intake to adequate levels would be better than trying to shore up an inadequacy with supplements.
As I mentioned above, I’d note that simply ensuring sufficient carbohydrate during training usually does more to keep immune system functioning well than anything else. The combination of carbs and small amounts of high quality protein (e.g. whey) should be sufficient under most conditions but endurance athletes doing very high volume might consider additional BCAA.
Resistance training, in general, tends not to have the negative effects on immune system function that high-volume endurance training does. I suppose athletes who were doing very high volume resistance training on a near daily basis might have issues but I’d see that as a problem with their training program more than their nutrition. And given that athletes involved in resistance training typically consume a lot more protein than the average endurance athlete, BCAA intake will go up automatically without the need for supplementation.

Summing Up
Quickly summing up this article, I looked briefly at BCAA and glutamine in general in terms of their metabolism before looking at two pathways of interest to athletes that might impact on specific amino acid requirements.
The first was energy use during exercise; generally relegated to endurance athletes only, there is evidence that the BCAA can be burned directly for energy during exercise, conceivably raising requirements. Studies have shown that the consumption of small amounts of protein during endurance exercis can limit muscle damage and may improve both recovery and performance. I feel that whole proteins such as whey will generally be superior to isolated supplements.
Resistance training, in general, doesn’t burn protein for energy unless the workouts are very voluminous and very long. While amino acid or protein intake during resistance trianing can still be valuable (for reasons I’ll discuss in Part 3) it has less to do with energy provision and more to do with overall adaptation and growth.
There are other pathways such as connective tissue and immune system function that are likely to be upregulated by heavy training; unfortunately these are poorly studied. Immune system is an area of great interest; while early studies suggested a role for glutamine in protecting the immune system during periods of high-volume training, not all studies were positive and BCAA probably play a bigger role by protecting glutamine status in the body.
At the end of the day, consuming adequate carbs during training (with or without small amounts of protein) doesmore to protect immune function but athletes involved in very heavy high-volume training might consider extra BCAA to keep from getting sick.
In Part 3, I’ll take a detailed look at the adaptations that occur with training along with how they might impact on amino acid requirements; again focusing on the BCAA and glutamine. I’ll also touch on dieting since that is a topic of much importance and relevance to many people.
I know this series is getting long and some folks want me to wrap it up and get to the point but I have a lot to say and a lot of information to cover. I will finally answer the original question What are good sources of protein? at the end of this series and give specific recommendations. So please be patient.

**gleke** · 23-10-2012, 20:04

What Are Good Sources of Protein? – Amino Acid Profile Part 3
In What Are Good Sources of Protein? – Amino Acid Profile Part 2, I looked a little bit at both the branched-chain amino acids (BCAAs) and glutamine before examining two distinct pathways by which exercise not only increases overall protein requirements but might impact on the specific amino acid profile needed by the body to support heavy training.
In the final part of this sub-series within the series, I want to look at the final way that training can potentially impact on specific amino acid requirements. I’ll also touch on dieting at the very end.

Exercise and Amino Acid Requirements: Skeletal Muscle Adaptation
Although there are certainly other adaptations occurring to training (e.g. neural, cardiovascular), one of the primary places where adaptation to regular training occurs in skeletal muscle. Both endurance training and heavy resistance training stimulate specific adaptations in skeletal muscle that work to improve performance in the long run.
Something to keep in mind is that resistance training and endurance training stimulate very different adaptations. Resistance training generally causes an increase in the actual contractile tissue in skeletal muscle; in contrast, endurance training stimulates increases in mitochondria along with the enzymes responsible for energy production.
In premise this means that strength/power athletes (who typically engage in heavy resistance training) and endurance athletes might require different amounts of specific amino acids to support the specific adaptations in those tissues. Without going into a lot of detail, it simply doesn’t work that way.
Quoting again from The Protein Book:
The liver acts essentially as a gate to ensure that the AAs which are required by the body are released into the bloodstream while any that aren’t needed are simply disposed of via oxidation. Even if a protein with the absolutely identical AA profile to skeletal muscle was consumed, this in no way guarantees that AAs in that proportion will appear in the bloodstream in the first
place.
As an example of this, you might recall from What Are good sources of protein – Speed of Digestion Part 1 that whey consumed by itself simulates amino acid burning; essentially any time the body sees an excess of aminos compared to what’s needed, it will simply burn off the excess aminos.
Now, one possible exception to this are the branched chain amino acids (BCAA) which I’d remind you are leucine, isoleucine, and valine. Unlike other amino acids which can all be degraded in the liver, the BCAA are used primarily in skeletal muscle.
In a very real fashion, the BCAA are muscle food and there has been huge interest in BCAA, especially among the weight lifting subculture, and for seemingly good reason.
It’s been known for years that the BCAA themselves can specifically turn on protein synthesis in skeletal muscle and, more recently, it’s been found that this effect is specific to the amino acid leucine (which works through a molecular receptor called mTOR).
Put simply: leucine turns on protein synthesis and this has led to the suggestion that lots of BCAA around training, or extra leucine, can be useful to stimulate protein synthesis.
And there certainly seem to be studies to support that. However, they all suffer from the same major flaw in my opinion: they are looking at BCAA supplementation in the context of insufficient protein intake. Or they are looking at older folks who, as I mentioned in a previous part of this series, respond to protein differently than younger folks.
As an example, one study that is being cited currently compared either a small amount of protein (~13 grams per hour) with carbs to a small amount of protein with an absurd amount of leucine (the same 13 grams of protein with an additional 6 grams of leucine) taken post-workout. Not only did the leucine only have a tiny effect, what’s not mentioned about this study is that the drinks were given for 6 hours after training which is hardly relevant to a single post-workout drink. As well, 13 grams of protein is far below what’s optimal post-workout; had sufficient protein been given in the first place, I doubt the extra leucine would have done anything.
As another example, one of the classic studies cited to support BCAA around training was an Italian study that compared the impact of BCAA to NOTHING on strength improvements. Of course the BCAA was superior because consuming something around training is going to be better than consuming nothing around training. But what if they had compared it to whey protein during training? Or whey plus carbohydrates (my recommendation). Would the BCAA still have been superior? I doubt it.

There is the additional fact that even if you stimulate protein synthesis with BCAA or leucine specifically, it won’t matter if there aren’t sufficient amounts of the other aminos present. You can turn on protein synthesis all you want with BCAA or leucine, without the other building blocks for skeletal muscle, it won’t make any difference. There is also the simple fact that the primary stimulus for increased muscle in the body is training, not protein. Most Americans eat tons of protein and get lots of BCAA, they aren’t growing muscle because they aren’t training and giving the body a stimulus to store the extra protein.
You can turn on all the protein synthesis that you want with dietary modifications, as it turns out the body simply breaks down more protein later in the day to compensate. Unless someone is training, muscle mass simply doesn’t increase due to these kinds of dietary manipulations.
Finally is the issue I talked about in What are good sources of protein? – Amino Acid Quality Part 2: all high quality proteins contain lots of the BCAA in the first place, ranging from 15-25% depending on the source (most sources are around 15%, casein comes in around 20% and whey can range from 23-25% BCAA). Of that BCAA, a fairly large chunk is leucine.
A bodybuilder consuming say 250 grams of protein (e.g. 1.5 grams per pound at around 170 pounds) will be getting, somewhere between 40-50 grams of BCAA depending on the sources. Someone consuming a lot of whey or casein will get a bit more, someone living on nothing but meat will get slightly less. But someone eating that much protein is already getting a lot of leucine in their diet, at each meal; throwing in another gram or two is not going to do much.
The same holds for BCAA as a whole; I just see it as unlikely that, unless someone adds a truly absurd amount, it’s going to matter in the context of the already large amount of BCAA coming in. And, as noted above, unfortunately the studies don’t really answer that question; they all look at BCAA supplementation under conditions of what I consider inadequate protein in the first place.
I would note that around training nutrition may be a slightly different situation, as I discussed in Milk: The New Sports Drink – A Review, milk protein was superior to soy for promoting lean body mass gains although this probably had as much to do with speed of digestion (milk protein was slower than soy) as amino acid profile per se.
There was also some indication that the soy protein, because of its amino acid profile, was preferentially used by the gut and this may have played a role. Again, around workout nutrition appears to be a place where things are a little bit different than the rest of the day, simply because of the acute increase in both protein synthesis and breakdown. Around workout nutrition is discussed in extreme detail (35 pages worth of detailed information) in The Protein Book.
But assuming an athlete is coming sufficient amounts of high-quality protein from mixed sources, and eating enough calories, there is simply no reason to believe that any protein source will significantly impact on adaptation to training or preferentially support adaptations in either contractile tissue or mitochondrial function.

Dieting
A final topic I want to discuss before I wrap up this series next week is the issue of dieting. Throughout the discussion about protein quality and amino acid requirements, one of the assumptions I’ve been making (along with high-quality proteins from mixed sources) is that sufficient calories are being consumed; clearly this isn’t the case when dieting.
It’s been known for at least three decades that total protein requirements go up during dieting; while bodybuilders were perhaps the first to realize this, research is finally catching up with their empirical knowledge.
Recent studies have found that ‘high-protein’ diets (and this is usually defined in terms of the percentage of protein in the diet) are superior for dieting for a number of reasons: research has found that high protein diets keep people fuller (making it easier to keep calories controlled), help to prevent some of the metabolic slowdown that otherwise occurs, spares lean body mass and helps to stabilize blood glucose.
While dieting, the body tends to use more amino acids to produce energy, both the branched chain amino acids and alanine are used in the liver to produce glucose and this is probably where much of the increased requirement for those aminos comes from. In that alanine in skeletal muscle is produced by the metabolism of glutamine, this might suggest an increased glutamine requirement during dieting.
But other than simply eating more protein, is any one protein optimal in terms of its amino acid profile? The answer is yes. One researcher has examined dairy proteins, and specifically leucine content, while dieting and has found that they tend to improve blood glucose maintenance and spare lean body mass while dieting. As I’ve mentioned throughout this series, I’m a big fan of dairy proteins (whey, casein, milk, yogurt) and this is one reason. You can read more of the reasons in Contest Dieting Part 1.
There is also some interesting evidence that fish protein (specifically cod as I recall) may improve insulin and possibly leptin sensitivity; it was suggested that this might be due to the specific amino acid content, especially taurine. This might explain why, empirically bodybuilders found that diets based around a LOT of white fish worked well.
Unfortunately, that’s about the limit of the research into specific amino acid requirements in terms of whole proteins. So what about supplements?
One study in wrestlers examined massive dose BCAA (~52 grams per day) and showed a slight increase in visceral fat mass and a sparing of lean body mass. However, it didn’t give adequate protein in the first place, the wrestlers were only given about 1.2 g/kg (a little less than 0.6 grams of protein per pound) which is less than half of what’s needed on a diet to spare lean body mass loss.
I’m only aware of one study that has examined glutamine directly for its effects on a diet; no effect was seen even at massive doses (35 grams per day). And while I’ve suggested small doses of glutamine to boost GH (GH has mild lipolytic properties as discussed in the Stubborn Fat Solution), no study has tested directly if this actually increases fat loss.

Summing Up
Both resistance training and endurance training increase overall protein requirements and the specific adaptations (e.g. contractile tissue in strength athletes, mitochondria in edurance athletes) seen with different types of training suggests that there might be optimal amino acid profiles to support the specific adaptations; little research has examined this.
As well, there are distinct physiological reasons, having to do with how the body as a whole and the liver specifically regulates blood amino acid levels, that makes this idea fairly untenable. The amino acid profile that shows up in the bloodstream tends to have very little relation to the amino acid of the proteins being eaten and the body will simply ensure that the aminos which are needed reach the target tissues and the ones that are not are disposed of.
Assuming sufficient high-quality proteins are being consumed in the first place, there should be more than enough of all of the amino acids present without any specific amino acid profile being required.
A possible exception to this are the branched chain amino acids (BCAAs) which generally escape liver metabolism and are used preferentially by skeletal muscle. While some studies have suggested role for BCAA in a variety of processes important to athlete (e.g. leucine specifically stimultes protein synthesis), every study that has suggested a benefit of BCAA or isolated leucine has done so within the context of inadequate dietary protein in the first place. Given a lifter consuming 3.0 g/kg (~1.4 g/lb) of protein, the high BCAA content of all high-quality dietary proteins make additional BCAA or leucine moot in my opinion.
One possible exception is around training where, at least in one study, milk protein was superior to soy protein in terms of promoting lean body mass; this had as much to do with the speed of digestion as the amino acid profile per se.
There is also evidence that, while dieting, high intakes of leucine and the BCAA may spare lean body mass and help to maintain blood glucose. Given the other benefits of dairy proteins as a whole (e.g. some aspect of dairy products increases fat loss), I’d suggest lifters focus on those whole proteins rather than isolated amino acids supplements per se.
In the next part of this series, I’ll start to wrap things up by looking at how the presence or absence of other nutrients (such as zinc, iron, the omega-3 fatty acids) impact on the answer to the question What are good sources of protein?
What Are Good Sources of Protein? – Micronutrient Content
As I move towards wrapping up this series this week, I need to discuss a couple of other topics of relevance to the question of what are good sources of protein. A good bit of what’s been discussed in other sections was a bit on the theoretical/sciency end of things and I’m going to keep the next couple of topics a lot more applied.
Today I want to look at an issue that I don’t think is addressed as much as it could be when folks are looking at protein source; that topic is the presence (or absence) of other nutrients. Outside of a few select groups (that often get a majority of their protein from isolated sources such as protein powders or amino acids), most people get their daily protein from whole food sources and whole foods contain other nutrients. Some of those nutrients may be beneficial, some of them may be detrimental; all need to be considered when looking at protein sources and deciding which are good, bad, or neutral.
The major ‘extra’ nutrients I want to look at in this article are zinc, iron, B12, calcium. In the next part of this article series, I’ll take a look at the issue of dietary fat content, both in terms of good and bad fats. This is simply to keep the length a bit more manageable.

Zinc
Zinc is an essential mineral involved in an amazing number of processes in the body including immune system function, appetite (a lot of early research showed that zinc deficiency did weird things to appetite, zinc has been shown to regulate leptin levels as well) and hormone levels (zinc deficiency can reduce testosterone levels). Since the body doesn’t store zinc, its intake is required on a daily basis.
Zinc is found to varying degrees in most protein foods with oysters containing the most zinc of any food (this probably explains the idea that oysters are an aphrodisiac, given the role of zinc intake on testosterone levels) Red meat, liver and crab meat contain the highest levels after that, chicken is a fairly close second. Eggs and milk are not fantastic sources of zinc although cheese has reasonable amounts.
Grains and cereals, along with beans (often a prime source of protein in vegetarian diets) are relatively poor sources of zinc. As well, compounds in these foods tend to impair zinc absorption in the gut.
Vegetarian diets are often zinc deficient and females (especially female athletes) who have a habit of removing sources of protein such as red meat and chicken also often come up zinc deficient. I’m a huge believer in lean red meat for most people, especially athletes and ensuring adequate zinc intake is one of those reasons.

Iron
Iron is another essential mineral, also involved in a staggering number of processes. Arguably the most well-known role of iron in the body has to do with keeping red blood cells healthy and working. A lesser known effect of iron has to do with thyroid conversion in the body; very low levels of iron can cause problems with thyroid production in the liver. Restoring iron levels to normal reliably improves thyroid conversion, can increase metabolic rate and improves thermoregulation.
In the diet there are two types of iron which are called heme-iron and non-heme iron. Heme iron is absorbed roughly 10 times more effectively than non-heme. Like zinc, the best sources of iron (especially heme iron) are meats, especially red meat, liver and organ meats. Chicken is also a good source of iron; interesting research has found that both red meat and chicken contain a factor that improves non-heme iron absorption by the body.
While many non-meat sources contain reasonable amounts of iron (and many food are iron fortified in the modern world), the iron is typically of the non-heme variety; as well the presence of other compounds in those foods often impairs the iron absorption. I’d note that vitamin C increases iron absorption and consuming some with iron containing foods is one way to improve iron absorption; cooking with a cast-iron skillet also increases the iron content of foods.
Females, due to the loss of menstrual blood each month are at a higher risk for iron deficiency than men (in this vein it’s interesting to note that women are more likely to have thyroid problems, I have to wonder if these two issues aren’t related) and females (especially athletes) along with vegetarians are likely to be iron deficient. This is especially true for female athletes who have a habit of removing red meat out of their diet. That, along with possibly increased requirements from training, along with slight blood losses each month add up to iron deficiency.
I’d note that too much iron can be as bad as too little, iron acts as a pro-oxidant in the body; men should be very careful about going out of their way to take extra iron and many multivitamins for men have no iron in them for this reason. While women lose some iron each month, excessive iron intake can build up stores in men and cause many problems.
Basically, as with zinc, meat protein, especially red meat is the winner here. This is yet another reason that I think lean red meat (which has also been shown to lower blood pressure and improve blood lipid levels) should be part of any healthy diet. Female athletes especially should probably be consuming lean red meat multiple times per week; supplementation may also be necessary.

B12
Vitamin B12 is, as its name suggests, one of the B vitamins. It plays critical roles in the body not the least of which is brain function. While B12 requirements are staggeringly tiny, and the body can actually build up a fairly long store of B12 (in the liver), deficiencies are not unheard of.
B12 is ONLY found in animal source products and vegetarians are often at risk for deficiency for this reason. Females who remove animal source proteins from their diet are, as with zinc and iron, at risk for deficiency.
I’d note that there is an oddity with B12 in that a specific factor is required in the stomach for B12 absorption; some people lack this. Even with plenty of B12 in the diet, they don’t absorb it and can end up with deficient. This can cause something called megoblastic anemia (this is a bit of weirdness to do with red blood cells) along with mental fuzziness. People who lack the absorption factor can’t simply supplement normal B12, they have to get a specific form called Methylcobalamin and this will have to be taken forever to avoid deficiency.
For everyone else, simply ensuring sufficient protein intake from animal source proteins will provide plenty of B12.

Calcium
Finally, I want to talk about calcium. Known primarily for its effects on bone health, calcium is turning out to play a number of other major roles. Early research found an effect on blood pressure of high dairy intakes and more recently some work has found an impact of calcium (and dairy foods seem to work better in this regards) on fat loss; the mechanism is still unclear although calcium may be affecting fat absorption from the gut, fat oxidation in the body, or some other aspect.
As well, the exact reason that dairy calcium seems to work better is an issue of some question; it may be due to greater absorption of dairy calcium compared to non-dairy calcium or it may have something to do with another factor inherent to dairy products.
The most well-known source of calcium in the human diet is, of course, dairy products. While there is calcium in many vegetable source proteins (vegetarians often claim that broccoli has more calcium than milk), the presence of other compounds in vegetables impairs absorption of the calcium that is present. Meats, grains and nuts are a poor source of dietary calcium.
I’d note, tangentially, that while there has been a long-standing belief that high-protein intakes are bad for bone health but this isn’t supported by current research. As detailed in Protein Controversies, a high protein intake is only a problem when calcium intake is insufficient; a high protein intake along with plenty of calcium actually improves bone health.
As discussed The Protein Book, I am a big believer that low-fat dairy products should be part of any healthy diet. Not only do dairy foods provide an excellent combination of slow and fast proteins, they provide the most available source of dietary calcium and seem to improve body composition and calorie partitioning.
As well, as I discuss in Contest Dieting Part 1, I also think that the weird bodybuilder ideas about dairy on a contest prep are not only invalid but actually do more to harm fat loss than anything else.
Of course, not everyone can consume dairy, either due to a true allergy (which is rare) or a lactose intolerance (which is more common). Of course, lactose free dairy products do exist (for example, Lactaid Milk) and there are pills of varying sorts which help with lactose digestion (either by providing the necessary enzyme or helping the gut to start producing more naturally). Failing that, calcium supplements would be indicated for someone who can’t consume dairy (for whatever reason).

Summing Up
There are a number of important micro-nutrients that can go into the decision of What are good sources of protein. Zinc, Iron and B12 are all critical nutrients which are found in the largest and most well-absorbed amounts in animal sources foods. Lean red meat (to avoid excessive fat intake), chicken, seafish can all be good sources of those foods; vegetarians and others who try to limit their intake of those foods (for either good or bad reasons) can be at risk for deficiency.
Dietary calcium plays an enormous number of roles in the body; while the most well-known is bone health, current research indicates that sufficient calcium (and dairy calcium appears to be superior to non-dairy calcium) can lower blood pressure and decrease body fat levels through a variety of mechanisms. I strongly believe that no- or low-fat dairy products should be part of any healthy or athletic diet for those and other reasons. Individuals with lactose intolerance have a number of potential solutions but if dairy simply can’t be consumed, supplements are at least adequate.
In the next part of this sub-series, I’ll look at the issue of dietary fat and its presence or absence in various dietary protein sources. This will include a quick look at both the contentious issue of saturated fat as well as the importance of the omega-3 fish oils.

**gleke** · 23-10-2012, 20:04

What Are Good Sources of Protein? – Dietary Fat Content
Having looked at a few key micro-nutrients (iron, zinc, B12, calcium) in What are Good Sources of Protein – Micronutrient Content, I want to move towards the wrap up of this series by looking at another issue of importance in choosing protein sources. That issue is the dietary fat content.
Now, without going into a lot of detail, but due to some more ‘fringe’ nutritional groups in the Internet, I suspect many will disagree with this article. The reason is that some groups have decided that 40 years of nutritional research is flawed and biased, that the current beliefs about fatty acid intake and health are exactly the opposite of the truth, etc, etc.
When and if I ever bother to address such points (it’s usually about as useful as responding to the anti-milk people), I’ll go into more detail about this. For now, I won’t except to say that I find both extremes of the argument to be flawed.
Saturated fat isn’t the killer nutrient that some make it to be, nor is it healthful and beneficial; the truth, as always lies in the middle and whether a high fat intake or a particular type of fat is good, bad or indifferent depends on the context. The rest of the diet, activity, body-fat stress, etc. all determine what is good, bad or otherwise. For more details, I’d refer readers to my two part article Carbohydrate and Fat Controversies where I go into detail as to my take on a lot of this argument.
And with that out of the way, let’s get started.

A Primer on Fats with a Bit on Cholesterol
There is often a lot of confusion regarding the issue of dietary fat not the least of which is a common misunderstanding between the issue of dietary cholesterol and dietary fat. Simply, cholesterol and dietary fat are completely distinct chemical compounds. The confusion, mind you, came out of the early research dealing with diet, dietary cholesterol, dietary fat intake, and blood cholesterol levels.
There’s a lot of confusion in this regards but this article isn’t the place to clear it up; at some point in the future, I’ll do a full feature article or series about dietary fats, for now you get the short version.
Dietary cholesterol is only found in products of animal origin and is completely chemically distinct from dietary fat in terms of the molecular structure. Without going into immense detail, the intake of dietary cholesterol really isn’t a big deal outside of a small subsection of folks who appear to be sensitive to it. So I won’t say more about it here.
Rather, I’ll focus on dietary fats. Dietary fats are more accurately called triglycerides which refers to the fact that each molecule is made up of a glycerol backbone attached to three fatty acid chains. It’s the fatty acid chains that are of interest as their chemical structure determines not only what the fatty acid is called but what effect it has on the body. There are four major categories of triglyceride which are
Saturated fat: these are found almost exclusively in animal products (with a couple of exceptions), are generally solid at room temperature and are generally blamed (somewhat unfairly) for a lot of health problems, especially increased blood cholesterol levels. And while some saturated fats certainly do raise cholesterol levels, others have no real effect.
Unsaturated fats: Unsaturated fats are typically liquid at room temperature and tend to be found to some degree in most foods that contain dietary fat; quite in fact, red meat (which is usually thought of as a major source of saturated fat) and eggs both contain a majority of their fat as unsaturated fat. In general, unsaturated fat is fairly neutral metabolically.
Polyunsaturated fats: Polyunsaturated fats are also liquid at room temperature and found in foods of vegetable origin. Polyunsaturated fats comes in two primary types: omega-6 and omega-3 fatty acids. Many readers are probably more familiar with the omega-3 (or w-3) fatty acids as fish oils.
As a generality, the w-3′s have extremely positive effects on health; an excess of w-6 has been thought to cause some health problems (especially in the context of insufficient w-3) although recent research is starting to question this. I realize that this last statement is a bit confusing but I don’t have space to explain it here. Since omega-6 fatty acids are found primarily in vegetable source foods, they really aren’t that critically relevant to an article on protein.
Trans-fatty acids: Along with high-fructose corn syrup, trans-fatty acids are a favorite whipping boy of people who want simple explanations for the complexities of modern health problems. Trans fatty acids do occur naturally in foods (a point missed by many of the anti-trans fat crusaders) but the majority realistically come from prepackaged man-made foods. Trans-fatty acids are made by bubbling hydrogen through vegetable oils, this produces a fat that is chemically modified but incredibly shelf-stable.
Good for food companies, maybe not so good for human health. A question is just how much trans-fatty acids the average diet will actually contain; of course this will depend on how much of those foods are eaten. Since trans-fatty acids don’t occur in massive amounts in most whole protein foods, I’m not going to mention it further.
There are also some odd fatty acids that are occasionally encountered. Medium chain triglycerides (MCT, so named because of their medium length) are found naturally occurring in some foods, as is conjugated linoleic acid (CLA).
I’m not aware of any protein source that contains significant MCT (coconut, of all things, is has about 50% of its fat as MCTs) so I won’t talk about it in any more detail. CLA is found in dairy products in small amounts. I’d note that most human research on CLA hasn’t been terribly positive; the fat loss effects seen in animals rarely show up and some data has found that CLA can cause insulin resistance. The amounts found in most foods are pretty tiny anyhow so it’s likely to be fairly moot; I bring it up only for completeness.
And with that introduction out of the way, I want to talk about the issue of dietary protein and dietary fat in terms of answering the question what are good sources of protein.

The Fat Content of Protein Foods
As with the issue of micro-nutrients, the presence or absence of dietary fat (either in terms of the quantity or quality) can impact on the choice of protein source. And this actually turns out to be a place where dietary fat content can vary massively, not only between protein sources but between different sources of the same protein.
As a singular example, while very lean red meat containing no more than 4 grams of dietary fat per 4 oz serving can be found at many stores (we get ours at Wal-Mart), it’s equally possible to find cuts of red meat that contain 20-30 grams of fat in that same 4 oz serving; a 6 to 8 fold difference. Other protein sources can show similar variance. I’d note that while isolated protein powders are typically extremely low in fat, this isn’t universal; there is actually a whole-egg protein that contains quite a bit of dietary fat, it’s quite creamy tasting.
With that said, I want to look at various whole food protein sources and how their fat intake might impact on whether or not they make a good protein source.

Red meat
As mentioned, the fat content of red meat can vary massively. And while many have the idea that red meat is primarily a source of saturated fat, a quick look at the USDA database shows this to be false. Perhaps half of the fat content of beef is saturated with most of the rest being unsaturated, with a small amount of polyunsaturated fat usually present. I’d note that grass fed beef can actually have a better fatty acid profile than this.
Chicken
Like beef, the fat content of fowl can vary dramatically. Cuts such as the thigh can contain quite a bit of fat while a skinless chicken breast may be essentially fat free. The fatty acid profile is similar to meat meaning that, while there is some saturated fat, the majority of the fat is actually monounsaturated with a small amount of polyunsaturates present.
Pork
Generally speaking, pork products are often high in fat; this can be especially true for prepackaged lunch meats (I’d note that low-fat ham is fairly readily available). A notable exception is pork tenderloin which is about as low-fat as the leanest chicken breast. Tasty, too.
Eggs
Whole eggs contain a moderate amount of fat, typically 5 grams in a single whole egg. I’d note that the white of the egg is essentially fat free and many fat-obsessed athletes have gone the egg white route for this reason. It’s worth nothing in the context of protein quality that while whole eggs have an extremely high quality rating, egg whites are not so good. It’s also worth noting that, Rocky movies notwithstanding, egg whites appear to be digested terribly. That’s in addition to any potential issues with salmonella poisoning. Cook your eggs before you eat them.
Now, eggs have been in a weird place nutritionally since the early ideas about blood cholesterol, many felt that due to the high cholesterol content (note again that dietary cholesterol has, at most a minimal impact on blood levels anyhow); if anything the saturated fat content of eggs was the bigger issue. At the same time, whole eggs are an extremely high quality protein and other nutrients in the eggs can be quite beneficial.
As it turns out, a lot of the scare over whole eggs turns out to be false, while a small percentage of people are sensitive even the American Heart Association has removed it’s recommendations to limit egg intake. Clearly individuals trying to limit total fat intake may still wish to limit eggs (or make egg related dishes with a mixture of egg whites and fewer whole eggs).
Like red meat, while a portion of the total fat in eggs is saturated, nearly half is monounsaturated with the remainder being polyunsaturated. I’d note that, recently, high omega-3 eggs have become available, these are made by feeding chickens large amounts of omega-3 fatty acids which changes the fatty acid profile of the egg.
I’d also note that, in the big scheme of things, unless someone is eating a tremendous number of eggs, obtaining a significant amount of w-3 in this fashion tends to be a losing proposition; it would be cheaper to eat normal eggs and take supplemental fish oils.
Fish
Like the other foods listed, the fat content of fish can vary massively. Low fat fish such as tuna is essentially fat free (hence it’s popularity with athletes) while higher fat fish such as mackerel can contain perhaps 12 grams of fat per 3 oz serving.
However, of some interest, and as the names suggest, fatty fish tend to be an excellent source of the healthy omega-3 fish oils. Quite in fact, much of the interest in the omega-3′s came out of the observation that ethnic groups such as the Alaskan Inuit had low levels of heart attacks yet consumed a lot of oily fish. Fatty fish contain quite a bit of monounsaturated fats (about half of the total) with a small amount of saturated fat as well.
However, the reality is that, in my experience at least, most don’t care for the fattier fish and trying to obtain a sufficient daily dose of omega-3 fish oils is probably unrealistic (I realize this comment is biased by my living in the United States where we just don’t eat those kinds of foods). It can be done but I don’t know, practically, how realistic is.
Dairy
Like the other foods discussed, the fat content of dairy foods can vary massively. Non-fat dairy foods are essentially fat-free (perhaps 0.5 grams fat per 8 oz serving) while whole-fat dairy can contain up to 8 grams of fat per 8 oz serving, 1% and 2% dairy products some in between those values. The fatty acid profile of milk is actually predominantly saturated with a small amount of monounsaturated fat and a very small amount of polyunsaturated fat.
As noted above, milk appears to contain a small amount of the fatty acid CLA; while this has shown impressive anti-cancer and fat loss effects in animals, these effects have not been seen in humans. Even if CLA were valuable to humans, it would generally take supplementation to reach significant intake levels.
Beans and Nuts
Although not often thought of as protein foods, beans and nuts can actually provide some protein to the human diet. And while most beans (tofu is a notable exception) are extremely low in fat, nuts can contain quite a bit of fat. However, a majority of the fat in nuts tends to come from the healthier monounsaturates and polyunsaturates. For example, a 2 oz serving of peanuts contains roughly 12 grams of fat of which nearly half is monounsaturated and most of the rest is polyunsaturated; the saturated fat content is very small.
And while the high-fat content of nuts might predict that they could cause problems with weight gain, as I discussed in the Q&A on Nut Consumption and Body Weight, the consumption of nuts doesn’t appear to have negative effects on body weight as a general rule.
Soy
Although they are technically a bean, soy tends to have enough issue surrounding it to deserve it’s own specific mention. Most of the issue having to do with soy have to do with the phytoestrogen content. Detailing this is far beyond the scope of the article although I spend quite a bit of time on the topic in The Protein Book.
Unlike most beans, soy can contain some fat, a half block of tofu for example contains just under 7 grams of fat with about half of that coming from polyunsaturated sources, the remainder comes from an even split of saturated and monounsaturated fat.

Summary
So, following up from Monday’s article What are Good Sources of protein – Micronutrient Content, I’ve now looked at the issue of fat content. Without going into detail, there are four primary types of fat in the human diet which can have quite varying effects on human health.
Saturated fats tend to be thought of as negative although the reality is far more complicated than this, monounsaturated fats are fairly neutral and the polyunsaturated fats are generally thought of as healthy (this is complicated by the fact that w-6 and w-3 fatty acids have distinct effects on the body and too much of one or the other can cause health problems). Trans-fatty acids are man-made fats (primarily) that tend to have only negative health impacts; since they are not found in protein foods to a significant degree, they aren’t that relevant.
The fat content of most protein foods tends to vary dramatically. While nearly fat-free versions of most foods are available, many cuts or types of protein can be exceedingly high in fat. In that high-fat diets can certainly be one contributing factor to overweight, the fat content per se of protein foods is worth considering when deciding on what are good sources of protein. Individuals trying to limit fat intake, need to choose proteins sources (or types of protein within a given category) that do not contain excessive fat.
In addition, there is the issue of the type of fat present, the fatty acid profile of the food affecting how a given food might impact on the body. In contrast to many long-held beliefs, most meat proteins are not as high in saturated fat as most people perceive. Rather, the predominant fat is typically neutral monounsaturated fat; most of those foods also contain some proportion of polyunsaturated fat as well.
Fatty fish is an exception to the above as it tends to contain a significant amount of polyunsaturated fat including the healthful omega-3 fish oils. Foods such as eggs, dairy, beans/nuts and soy all weigh in at different places on this spectrum as well, as discussed in the article.
Ok, we’re getting close to the end of this series. I’m going to use the next article as sort of a catch-all to cover any issues I haven’t discussed previously regarding different protein sources. I’ll finish up by providing an overview of this series to finally answer the question what are good sources of protein.

**gleke** · 23-10-2012, 20:07

What Are Good Sources of Protein? – Wrapping it Up
Ok, so this series got a little out of control; what can I tell you, I have a lot to say on the topic of dietary protein as a function of having written The Protein Book.
I’ve covered a lot of information ranging from the somewhat technical/theoretical (speed of digestion) to very practical (micro-nutrient content, fatty acid content) in an attempt to answer the question what are good sources of protein?
In this final part, I want to cover a few other issues that go into answering that question (that didn’t require a full-blown article of their own) and then I’ll finish by presenting a summary table where I’ll attempt to put everything from this entire series into a comparable perspective.
In What Are Good Sources of Protein – Introduction, I included a short list of other important factors such as effects on appetite and blood sugar that I already addressed in previous parts of this series so I won’t touch on them here. The issues I do want to touch on are availability, the actual protein content, and cost.

Availability
It should be obvious that whether or not a given protein source is good or not doesn’t matter if someone can’t get it. The ease of availability of a given protein in a given location is clearly an issue but not one I can speak to except in the most general of terms. What I have access to in the US has no bearing on what someone overseas can or cannot get; in fact I’m quite sure I’ve left out certain whole food protein sources simply due to being located in the US. What someone might have access to in Norway might not be available here and vice versa.
Protein Content
This may seem like an odd category in a series about protein but the simple fact is that all food containing protein don’t only contain protein. As discussed in What Are Good Sources of Protein – Dietary Fat Content, I made it clear that many ‘protein foods’ can contain a significant amount of dietary fat although this can vary massively. In a related fashion, some protein sources also contain carbohydrates. Depending on the goal of course, finding sources that contain a lot of protein compared to their total caloric intake may be one variable that goes into the question of what are good sources of protein.
Basically, what I’m talking about here is how much protein a given whole food provides relative to either the serving size or the total caloric content of that food. If a food provides an enormous amount of protein without providing excessive calories,that food has a high protein content; if it doesn’t, it has a low protein content.
Obviously, this is relevant from a caloric intake standpoint; a protein food containing a lot of carbohydrate and/or fat will have more calories than one that doesn’t. While studies are repeatedly finding that high-protein diets have many benefits, if trying to raise protein content leads to increased caloric intake, that’s not necessarily a good thing.
Looking at specific diets, many ‘high-protein’ diets are also meant to be low in carbohydrates. This means selecting protein sources that don’t contain too many tag along carbohydrate sources or the protein source itself ruins the diet. Similarly, athletes on high-protein but low-fat diets need to choose protein sources without a lot of tag along fats in them. You get the idea.
Now, protein sources based on meat (beef, chicken, pork, fish, eggs) contain, at most, trace amounts of carbohydrates. The exception might be if you ate them fresh after a kill (before the muscle glycogen degrades) but I doubt that describes many people. Individuals trying to raise protein while limiting carbohydrates tend to focus on such foods for that reason.
As discussed in What Are Good Sources of Protein – Dietary Fat Content, the fat content of such foods can vary massively from nearly none (skinless chicken breast) to very high (fatty red meat) and that can be a consideration depending on the situation.
I’d note that, typically, meat protein will contain about 7 grams of protein per ounce. So a 3 oz piece of meat (about the size of a deck of cards) will generally have about 21-24 grams of dietary protein. The protein content of other foods depends on the food.
Dairy products generally always contain some carbohydrates although the amounts can vary. A typical 8 oz. serving of dairy will typically contain about 12 grams of carbohydrates. Cheese is an exception and is typically much lower in carbohydrate containing only small amounts. As noted in the last article, the fat content of dairy can vary significantly from essentially zero in fat-free dairy to moderate levels in full-fat foods.
Beans and nuts, for their caloric content, tend to be lower in terms of protein content due to the presence of tag-along carbs or fats; it’s also nearly impossible to find such foods that don’t have the other macro-nutrients. Beans generally contain a good bit of carbohydrate (along with a chunk of fiber), nuts contain a good bit of dietary fat. That is to say, while many animal based foods can provide essentially pure protein (with no carbs or fats), vegetable source proteins rarely can do this.
Vegetarians or individuals who obtain a lot of protein from vegetable sources who are trying to increase their protein intake via these foods invariably end up getting a lot of ‘extra’ calories from the other macros. This makes following high-protein/low-carb diets with such foods nearly impossible.
Typically, protein powders provide nearly pure protein with only trace carbs. And with the exception of the whole-egg protein powder I mentioned in the last article, few contain more than a gram or two of dietary fat under most circumstances. While I generally prefer that diets be based around whole foods (for a variety of reasons), protein powders can provide a very concentrated source of protein for individuals running into problems with other whole food protein sources.

Cost
An issue not often appreciated in answering the question of what is a good source of protein is the cost. Now, unfortunately, this is an issue that tends to be nearly impossible for me to address in any useful way because food costs vary massively. What I’m paying in the United States will vary greatly from town to town and I have absolutely no feel or perspective on what someone overseas will pay. Issues of availability, etc. will affect local food prices and I can’t cover this except in general.
What is often useful is to sit down and calculate out the effective cost per gram of protein for a given whole food protein source. Basically, you add up the total protein and divide that by the cost of that food to determine how much you’re paying per gram of protein.
For example, let’s say you can buy an average can of tuna fish (which typically has about 32 grams of protein) for 50 cents. And let’s say you can buy a cup of yogurt (8 grams of protein) for the same 50 cents. Finally, let’s say we can buy a pound of meat (which will contain about 120 grams of protein) for $4.50 (450 cents) per pound. We can compare each:
§ Tuna: 50 cents / 32 grams of protein = 1.8 cents per gram of protein.
§ Yogurt: 50 cents / 8 grams of protein = 6.25 cents per gram of protein
§ Red meat: 450 cents / 120 grams of protein = 3.75 cents per gram
Obviously the tuna fish is the cheapest, the red meat is second and the yogurt is the least cost-effective. Of course, that cost would be weighed against everything else in this series: issues of quality, other nutrients, etc. Even being more expensive, the dairy might be a better choice for someone wanting a mix of casein/whey along with the dairy calcium that seems to improve body composition.
I’d note that, depending on where you are in the world, protein powders are often far less expensive than whole foods. This is especially true in the United States but is often less so in other countries where shipping jacks up the costs of the powders massively. In any case, with a few simple calculations, you can determine the cost effectiveness of various types of protein.

And, Finally, the Wrap-Up
As noted, I’ve covered a tremendous amount of information in this series. Digestibility, Speed of Digestion, Protein Quality, Amino Acid Profile, Micro-nutrient Content and Fatty Acid Content. In this final article, I’ve looked at three additional factors including availability, protein content, and cost. In the chart below, I’m going to try to summarize everything I’ve talked about to provide readers with an overview of all of those topics. For what should be obvious reasons I haven’t included either cost or availability. This should help to finally answer the question What are good sources of protein?
protein?

Bodynet kan dit niet weergeven bekijk deze link voor de tabel.
What Are Good Sources of Protein? - Wrapping it Up | BodyRecomposition - The Home of Lyle McDonald

A couple of comments on the above chart. N/A simply means that there is nothing particularly noteworthy about a given food in a given category. For example, as I discussed in What Are Good Sources of Protein – Amino Acid Profile, the amino acid profile of most foods is more than sufficient to meet human requirements. As noted above, casein and whey are interesting due to their high content of the BCAA; some sources of soy isolates also contain significant amounts of BCAA and glutamine.
I didn’t talk about the phytoestrogen issue regarding soy protein; this is something I’ll address later on the site. I’ll only say now that the issue of phytoestrogen content is more complex than ‘they are good’ or ‘they are bad’. Again, this isn’t the place.
And that wraps it up. I suspect that some readers were hoping for a nice easy list comparing ‘good’ and ‘bad’ protein sources; unfortunately, the real world tends to be a lot more complex than that. Issues of speed of digestion, digestibility, amino acid profile and micro-nutrient content all goes into determining what is a good source of protein under a given context. The best protein for someone on a low-fat diet attempting to deal with high blood cholesterol is not the same best protein for an athlete looking to maximize adaptation to training.
In general, low fat animal products tend to provide the best quality, highest digestibility, and greatest micronutrient content compared to vegetable source foods; I’m clearly a big fan of dairy proteins for reasons outlined throughout this series. Low-fat meats, dairy, etc. all provide excellent sources of high-quality protein.
Vegetable source proteins also have their own benefits, the fats in nuts are excellent, the fiber content of beans is important to protein nutrition; that’s along with being a decent source of quality protein. Nuts seem to blunt appetite and might be useful for individuals involved in active fat loss. In combination with other high quality sources, vegetable source proteins can add both protein and other important nutrients to the diet.
Of course, protein powders have been used extensively in the athletic world and have even become part of the general nutrition and dieting lexicon. Whey and casein tend to be the ones most focused on but soy proteins are high quality and may raise anti-oxidant status in the body; the phytostrogen issue is too detailed to cover here but I will cover that in a later article.
In any case, hopefully in this series, I’ve covered most of the issues of great importance regarding the topic and given readers sufficient information to make protein choices for their own specific contexts. As noted throughout the series, more detailed information can be found in The Protein Book.
And hopefully, once and for all, this series has answered the question What are good sources of protein?

**gleke** · 23-10-2012, 20:08

Dubbel.

**gleke** · 23-10-2012, 20:13

Zo daarmee staat alles erop, comments zijn nu toegestaan.
Voor de samenvatting verwijs ik naar het rode, alhoewel ik betwijfel of zelfs iemand dat zal lezen, maar goed.

En NEE, ik ga niet alles vertalen.

[Engels] What Are Good Sources of Protein?