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
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.
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) does more 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.