Posted on

Dietary Protein Sources – Protein Quality Part 2

In the previous section of this guide, 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  more than adequately meet the amino acid requirements of adult humans.  In the modern Western world, obtaining sufficient protein is not an enormous issue and quality is unlikely to matter enormously.

Amino Acid Requirements for Athletes

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.

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.

Branched Chain Amino Acids (BCAA)

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 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 AA 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 AA 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.

Exercise and AA 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, recall from my discussion of protein digestion speed that whey 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.

BCAA Activate Protein Synthesis

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).

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.

Some BCAA Reality Checks

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, as I discussed in the previous part on dietary protein quality, 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.

Around Training Nutrition

I would note that around training nutrition may be a slightly different situation.  As I’ve discussed previously, 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 and Protein/Amino Acid Requirements

A final topic I want to discuss is how dieting can impact on protein and amino acid requirements.  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 and increasing fat loss 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 of many reasons.  It’s also why I question the common practice of removing dairy from the diet when maximum fat loss is the goal.

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.

A Summary of Protein Quality/AA Profile

Both resistance training and endurance training increase overall protein requirements and the specific adaptations (e.g. contractile tissue in strength athletes, mitochondria in endurance 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 stimulates 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.

Read Dietary Protein Sources – Other Dietary Factors


Facebook Comments