Protein and Amino Acids, 1997
Pp. 285-288. Washington, D.C.
National Academy Press
ROBERT NESHEIM: I'd like to open this up now for discussion. Dr. Rennie, how would you respond to the questions posed by the Army?
MICHAEL RENNIE: Regarding whether active people need more protein, I think that looking at people who live under circumstances of low protein intake gives us a lot of the answers. If you look at the protein intakes of Kenyan runners, they eat something like 0.6 to 0.7 grams of protein per kilogram per day, and they outperform all of the Western middle- and long-distance runners, right?
So there are natural experiments that suggest that you don't need to eat very much protein to do well in certain kinds of physical performance. Of course, I don't know how well they would do as weight lifters.
I don't want to steal the thunder of Anton Wagenmakers, but it strikes me that all of the studies that have been done by giving individual mixtures of amino acids, either branched-chain amino acids, glutamine, or glutamate, have, without exception, shown no effect on physical performance.
I don't want to steal Harris Lieberman's thunder, either, but I strongly suspect that unless there are kinds of cognitive function that we cannot measure easily, you will not see much in the way of any effect on cognitive performance.
Finally, I think that there are just insufficient data to talk about gender differences so far.
HARRIS LIEBERMAN: I just want to make a comment. With regard to formulating a recommendation, remember that the soldiers who come into the Army are eating an American diet and have eaten an American diet their whole lives, so that a suggestion that I make is not to recommend a change in the American diet or even a change in the soldier's diet in garrison, because we really cannot change diets that drastically; we simply want recommendations on what we are going to feed in those times when we go out into the field, and particularly when we go into combat. What we really need is a recommendation for a combat ration.
ROBERT NESHEIM: Dr. Butterfield?
GAIL BUTTERFIELD: Let me ask my usual question of the speakers. One of the problems with military troops in the field is that their energy intake is dramatically reduced. How do you think that reduction will affect these various factors?
MICHAEL RENNIE: Well, there is some dramatic evidence from Stroud and Fiennes' trans-Antarctic walk, in which they expended huge amounts of energy, greater amounts of energy than Tour do France cyclists expend, and yet their energy intakes were certainly less than that, and they lost very large amounts of weight.
What is quite interesting is that in the study that Stroud and Alan Jackson and John Waterlow published in the British Journal of Nutrition , although it cannot really be described as a scientific study, given the way the controls were performed after the event, nevertheless, it is quite interesting that whole body protein turnover did not appear to be markedly depressed, despite the fact that these people were in marked energy deficits, (much more than I imagine any scientist would ever get permission to induce under these circumstances). Presumably, protein balance was maintained because the subjects were taking in a fair amount of nitrogen; I cannot remember exactly how much. But they were also exercising at these very high rates.
So the idea that exercise was somehow making protein utilization more efficient, I think, is borne out by that kind of study.
ROBERT NESHEIM: Yes, Nancy?
NANCY BUTTE: Another question we have been asked to address is the potentially detrimental effect, of high protein intake or supplementation of a single amino acid on a woman who is pregnant.
In the military now at any one time, 8 to 9 percent of active duty women are pregnant. Many of these pregnancies are unplanned, so there is a period where a woman may not be aware she is pregnant. Could some of our experts in protein comment on a possible detrimental effect of either a high protein intake, high protein-to-energy ratio, or a single amino acid supplementation?
D. JOE MILLWARD: I don't know of any evidence to suggest that there is a problem. I mean, I cannot ever remember reading any detailed consideration of that question at all, and it is difficult to really identify one off the top of my head.
ROBERT WOLFE: I wanted to just follow up and ask Mike Rennie his opinion. I think that one of the problems with this whole issue of exercise and amino acid requirements, is that because of the limitations of methodologies, where we are limited to certain types of exercise (such as moderate aerobic exercise) that have been studied, these may not always have a parallel in troops sent into combat.
Mike referred very briefly to the situation of overtraining, and it is certainly clear, with overtraining, for example, that you get disruption of normal amino acid concentrations in the muscle and that maybe in this circumstance, the protein requirements are different than for someone who is just doing moderate exercise at a very easy level. But someone who is thrust into repetitive and high-intensity exercise clearly ends up with a different response in their muscles, and this difference is something that we should think a little bit about. Even in more general terms. We need to think about the difference between resistance exercise and aerobic exercise. We tend to move back and forth between the two, but I don't know that that is really justified, and if the goal is to build up strength, then simple maintenance of nitrogen balance may not really be the end goal.
MICHAEL RENNIE: I agree with all of those points.
D. JOE MILLWARD: Can I comment on that? I think part of the difficulty that I see here is that if the ultimate objective is the overall performance of the individual, then one has to avoid thinking about one system in particular.
For example, we know that individuals involved in large amounts of exercise, like marathon runners and certainly overtrained individuals, tend to
have a reduced immune function. The research that has shown glutamine supplementation to be effective has been under circumstances where the glutamine is protective against the consequences of reduced immune function, like preventing bacterial translocation across the gut and those sorts of things.
Now, the link [between the immune system and physical activity] would be the problems promoted by leakage of muscle enzymes as a consequence of large amounts of physical activity, which promote an acute phase response, coupled with loss of muscle glutamine and the consequences of that loss.
And so, if you need to think about whether glutamine supplementation would be important in those circumstances, although we think of muscle as the main store of glutamine, you actually have to think of the function of glutamine, which is really on the gut and on the immune function. Thus, unless you actually think about the whole picture, I think you are going to miss some of the outcomes. That is why, ultimately, the studies that must be done must define as many different parameters as possible in terms of performance and include those parameters. So far, we have attacked little bits of the problem with individual studies, and that is why I think it is so hard to put the whole lot together and come up with a sensible answer.
ROBERT NESHEIM: I think that brings us to the next set of presentations, which have to do with cognitive performance, stress, and brain function.