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 adeequate 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.

Go to What Are Good Sources of Protein – Amino Acid Profile Part 2



12 thoughts on “What Are Good Sources of Protein? – Amino Acid Profile Part 1

  1. I’m really interested in these series, but I have lots of questions popping out. For example, you said: “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).”

    My question: How come it doesn’t work (maybe you are talking solely about fat metabolism)? I’ve read articles (by Dave Barr) and seen studies that state that carnitine-L-tartrate increases androgen receptors in muscle and nerve cells, thus improving testosterone function and recovery.

    I also have questions about leucine, but I’ll wait until Monday’s article and then post them 😉

  2. I was specifically speaking about fat metabolism. And oral supplementation doesn’t work to increase fat metabolism because it is ineffective at increasing skeletal muscle levels of carnitine. Some resaerch suggests that you can make it work with very high dose insulin infusion, since this appears to increase uptake into the muscle. But it takes a lot.

    I have seen the research suggesting it may impact on androgen receptor sensitivity.

    As note, literally all of this is covered in excruciating detail in The Protein Book . All the supplements, all the research, all the rationale. I’m just covering the basics here.


  3. How about cutting to the chase? Provide everyone a list of good protein sources. Provide a list of protein sources to avoid. Honestly I could care less about the science.

  4. Barry

    This is how I do things.

    If you don’t care about the science, don’t read the articles until I wrap it up at the end.

    Clearly the rest of my readers don’t agree with you so (or they haven’t taken time to say so) so you might see why accomodating you (and ignoring what they want) isn’t very likely to happen.


  5. Thanks for very quick response! I would like to see studies that say that carnitine is useless for fat loss.

    As for carnitine and androgen receptors, I see that you didn’t criticize it, so I assume it’s all good to use it for that 😉

  6. Lyle, I think I read in one of your works (UD2.0?) that it may be beneficial to take some glutamine right before bed. I think you said it may help with HGH production? Can you comment more on that aspect of BCAAs, and why that may be better than eating some meat right before bed? It would seem to be relevant to the BCAA discussion, though perhaps you will discuss it in Part 2 of this series. Thanks.

  7. thnx a lot ……………….please tell me more about amino acids ,whether i should take it or not , i also do workout in the gym,tell me more about diet ,,,,,,,

  8. “But from the standpoint of amino acid profile, there isn’t much of a functional difference between proteins”

    so whey, soy, carrot, onion… you really mean this?

  9. Important to keep it in the context of the section heading which was:

    Meeting Basic Bodily Requirements

    in that specific context, pretty much all foods tht contain protein meet the amino acid requirements of humans. And carrots and onions aren’t massive protein containing foods. The chart demonstrating this (showing AA requirements for adult humans compared to the AA profile of a variety of high-quality proteins) is in The Protein Book. Basically all proteins (of even moderate quality) exceed human requirements. thus there is no functional difference. Eat sufficient total protein and you’re fine from the standpoint of meeting basic bodily requirements.

    Again, carrots and onions aren’t major protein containing foods so that’s just a stupid example.

  10. most people on forums say glutamine is worthless at low doses (they say megadose 20g+) because that was shown to work on burn victims in some study. Some people swear by it though.

  11. Lyle, what do you think about cow’s milk being deleterious for humans? I recently briefly read a summary of a study suggesting that cow’s milk is only good for baby cows (Casein: A Milk Protein with Diverse Biologic

    Is there reason to worry if I’m drinking it?
    What if I only took supplementary micellar casein? Would that also not be a good idea, or would it be safer than the bovine casein the article refers to due to the way it is processed?

Leave a Comment