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
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.
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.
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?