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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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14
Performance-Enhancing Effects of Protein and Amino Acids

Carol E.Greenwood1

INTRODUCTION

The objective of this chapter is to consider whether manipulations of dietary amino acids (AAs) can be used to enhance the performance of military personnel in combat situations. The ultimate concern is whether the combined physiologic and psychologic stresses associated with combat situations, which can lead to negative effects on the performance of the individual, can be overcome or minimized through the provision of specialized diets or AA supplements. Time frames involving both acute and chronic administration will be considered, and the following questions will be asked. First, can the performance of an individual be influenced over the short term (several hours) by provision of specialized meals or AAs? Second, since military personnel may find themselves in combat situations for prolonged periods of time, can the overall diet be modified to help individuals overcome the continuing stress associated with combat situations?

This chapter specifically deals with the potential performance-enhancing effects of AAs. AAs can be provided to the individual either as intact proteins

1  

Carol E.Greenwood, Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Baycrest Centre for Geriatric Care, North York, Ontario, Canada M6A 2E1

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

or in the free form. Furthermore, free AAs either can be administered as single supplements or can be incorporated into existing foods. Therefore, provision of AAs in all these forms will be considered.

EFFECT OF DIETARY PROTEIN: LONG-TERM CONSIDERATIONS

Under normal circumstances, the adequacy of protein in the typical North American diet is not a concern. The Recommended Nutrient Intake (RNI) (Health and Welfare, Canada, 1990a) for protein for Canadians meets or exceeds the needs of almost all individuals in the population. Furthermore, chronic levels of protein intake are well above the RNI (Food and Agriculture Organization of the United Nations/World Health Organization/United Nations University), 1985; Health and Welfare Canada, 1990a; National Research Council, 1980, 1985).

The relevant issue here is whether the chronic high levels of stress under combat situations influence the protein requirements of the individual. Unfortunately, direct experimental evidence is not available; however, there is evidence that the chronic physiologic stress associated with endurance training in athletes may raise protein requirements. The protein requirements needed to maintain the nitrogen (N) balance of bodybuilders and endurance athletes were 12 and 88 percent higher, respectively, in comparison with those of sedentary individuals (Tarnopolsky et al., 1988). If it is assumed that the physical demands of combat are analogous to those experienced by endurance athletes, then these data would suggest that protein requirements are indeed increased under combat situations. The 88 percent increase in protein requirements would raise the RNI for protein from 0.86 g/kg/day in adult males to 1.61 g/kg/day (Table 14–1). Under normal circumstances, the potential increase in protein requirements would be more than offset by the increased energy intake associated with high activity levels. For example, changes in nutrient intake were examined in Navy servicemen during a 5-day period known as Hell Week (Smoak et al., 1988), during which subjects are subjected to conditions similar to those anticipated under combat situations. During Hell Week, average energy intake increased from 18.7 to 24.4 MJ/day. This was accompanied by an increase in protein intake from 189 to 260 g/day (approximately 2.6 and 3.4 mg/kg/day, respectively, on the basis of reported average body weights of 72.9 and 75.6 kg, respectively, at the beginning and end of the experimental period), which could be accounted for entirely on the basis of increased energy intake. Clearly, even if protein requirements were increased during the simulation of combat conditions, the diet provided more than sufficient protein to meet these additional requirements.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

TABLE 14–1 Effect of Exercise on Protein Requirements of Athletes

Training Status

Protein Intake to Maintain N Balance (g/kg/day)*

Increase in Protein Needs to Maintain N Balance (percent)

Predicted Safe Levels of Protein Intake (g/kg/day)

Sedentary individuals

0.73

0.86

Bodybuilders

0.82

12

0.96

Endurance athletes

1.37

88

1.61

*Values taken from Tarnopolsky et al. (1988).

†The recommended safe level of protein intake for male adults (Health and Welfare Canada, 1990a) was used as the baseline for sedentary individuals. Predicted safe levels of protein intake for bodybuilders and endurance athletes were calculated on the basis of the percent increase in protein needs to maintain N balance.

Unfortunately, however, despite its intent, Hell Week is unable to simulate all situations associated with real combat. Under these conditions, actual food intake would be expected to decrease (see chapters 7 and 8), and the decrease may be severe enough that the individual is in both negative energy balance and negative N balance. Thus, perhaps of more relevance is the degree to which food shortage, in and of itself, has a negative impact on performance. The impact of energy deficit, in combination with food supplementation, on work performance was examined in Gambian subsistence farmers during a period of natural food shortage (Diaz et al., 1991). No benefit of food supplementation on work productivity could be detected. Thus, it would appear that, at least over the short term, food shortages or energy deficits do not impair an individual’s ability to perform physically demanding tasks. What was not addressed in that study, however, was whether higher forms of performance, such as cognitive performance including decision making, were influenced by the energy deficit. Obviously, it will be important to determine whether cognitive skills are sensitive to energy deficits and whether they can be improved with food supplements.

EFFECT OF DIETARY PROTEIN: SHORT-TERM CONSIDERATIONS

The degree to which short-term (meal-to-meal) changes in protein and carbohydrate (CHO) ingestion have an impact on mood and performance has

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

received considerable attention over the past several years (see chapters 17 and 15 for a more extensive review). These studies were a natural extension of research demonstrating that acute administration of specific AAs and/or ingestion of relatively pure CHO and protein sources could alter neuronal synthesis and perhaps the release of certain monoaminergic neurotransmitters (Wurtman et al., 1981). Given this area of research focus, it is therefore appropriate to ask whether controlled manipulations of the protein or CHO content of individual meals can produce desired performance outcomes.

Probably the most extensively examined aspect of protein ingestion is its influence on appetite regulation (Anderson and Li, 1987). Ingestion of high-protein meals is associated with satiety in both experimental animals (Li and Anderson, 1982) and humans (Barkeling et al., 1990). In comparison with high-CHO meals, intake of high-protein meals selectively reduces protein intake as well as total food intake in the subsequent meal. Whether these satiating effects of protein would continue to be observed under stressful conditions is unknown. Indeed, physiologic and psychologic changes associated with highly stressful circumstances could easily be hypothesized to override the normal signals that regulate appetite. Nevertheless, these research data open the possibility that high-protein meals may prolong satiety in the individual, and there may be certain circumstances in which this effect of protein ingestion could be used to advantage.

The mood or performance of the individual may also be influenced by the protein or CHO content of individual meals (see Chapter 17 for a more extensive review). That is, consumption of high-CHO meals in comparison with consumption of either mixed meals or high-protein meals may be associated with fatigue (Deijen et al., 1989; Spring et al., 1989). However, the response to CHO ingestion is variable and differs depending on the age and gender of the individual (Spring et al., 1982–83). Unfortunately, the degree to which behavioral effects of CHO consumption would be observed under combat situations is unknown at present because prior studies have been conducted under nonstressful circumstances.

ROLE OF INDIVIDUAL AAs OR MIXTURES OF AAs

Space limitations preclude an extensive examination of all AAs with regard to their potential performance-enhancing effects, and detailed reports on the impact of single-AA supplementation can be found elsewhere (Health and Welfare Canada, 1990b; (Federation of the American Societies for Experimental Biology, Life Sciences Research Office, 1992). At present, the most promising effect of AA supplementation appears to be with tyrosine (TYR).

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

The benefit of TYR supplementation probably relates to the fact that it is a precursor to the neurotransmitter norepinephrine and can increase norepinephrine synthesis under conditions in which the neuron is actively firing, such as stress (Wurtman et al., 1981). Provision of TYR under stressful conditions simulating certain combat situations may be associated with a reversal of the observed neurochemical changes and behavioral improvement (see Chapters 15 and 16 for an overview of the impact of TYR supplementation). Clearly, this area warrants further investigation.

There is little evidence at present that provision of other AAs will be of benefit (reviewed in Health and Welfare Canada, 1990b; Life Sciences Research Office, 1992). Indeed, most other AAs appear to have little or no behavioral effects in humans. The one exception may be tryptophan (TRP), which, at high doses, may be an effective hypnotic and useful in the treatment of certain forms of insomnia as well as a useful adjunct to monoamine oxidase inhibitors in the treatment of affective disorders (reviewed in Health and Welfare Canada, 1990b); however, this effect of TRP is unlikely to have application in combat situations.

Consideration should be given, however, to the provision of the branched-chain amino acids (BCAAs), isoleucine, leucine, and valine, as a mixed AA supplement. Early interest in this area related to observations that BCAA catabolism may be increased during prolonged exercise (Henriksson, 1991; Wagenmakers et al., 1989), and the question arose as to whether these AAs should be provided to replenish those presumably used by the exercising muscle. The degree of activation of BCAA catabolism after prolonged, intense exercise is small, however (Wagenmakers et al., 1989), and is not observed in all studies (Tarnopolsky et al., 1991). Furthermore, evidence suggests that proteins or AAs do not contribute substantially as an energy source during exercise (Henriksson, 1991; Wagenmakers et al., 1989). Thus, there appears to be little justification for BCAA supplementation on the basis of replenishing the BCAAs oxidized during exercise.

Nevertheless, there is a report of improved mental performance, measured as the performance in the Stroop Color and Word Test, in subjects given BCAAs during a 30-km cross-country race (Blomstrand et al., 1991). The authors suggest that this effect of the BCAAs may relate to changes in the plasma AA profile and uptake of other AAs, such as TRP, into the brain. Clearly, this area warrants replication and perhaps further experimentation.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

ROLE OF DIET IN MODULATING RESPONSE TO AA SUPPLEMENTATION

The background diet fed to an individual, the form in which supplementation is accomplished, and the frequency of AA supplementation may all have an impact on an individual’s response to AAs. Careful consideration of these factors must be taken to determine the most effective means of providing AA supplements.

Clearly, if the intent of AA supplementation, for example, TYR, is to raise brain AA levels, the least effective way to accomplish this is to incorporate the AA into prepared meals, especially those containing protein. This is simply due to the fact that plasma levels of other AAs that compete for the same brain uptake carrier will also rise following protein ingestion (Wurtman et al., 1981) . This is particularly important for the large neutral amino acids (LNAAs), including TYR and TRP, since relatively large increases in plasma levels of the competing LNAAs would be anticipated. The overall impact would be to minimize TYR’s or TRP’s ability to enter the central nervous system (CNS). Rather, the more effective way to increase brain TYR or TRP levels would be to administer it in the absence of other foods during a postprandial period when the plasma levels of the other competing AAs would be at their lowest.

In addition to this acute effect of meal ingestion, the protein level in the chronic background diet may also have an impact on responsiveness to AA supplementation. Plasma AA levels are not only reflective of recent meal ingestion but are also sensitive to the chronic level of protein intake (Glanville and Anderson, 1985; Peters and Harper, 1985). For example, when rats are fed diets that vary in protein concentration from 15 to 50 percent (w/w), and plasma AA levels are measured in the fasting state, a dose-dependent increase in indispensable AAs is observed (Peters and Harper, 1985), with the greatest changes being observed in the BCAAs. Because the BCAAs compete with other LNAAs for entry into the brain, it was postulated that the chronic background diet fed to an animal would influence the ability of the administered TRP to enter the CNS even when the TRP was given to fasting animals. Indeed, brain TRP levels were significantly lower in animals fed a 40 percent protein diet in comparison with those consuming a 12 percent protein diet (Table 14–2). Thus, it would appear that the lower the protein concentration of the chronic diet, the greater the likelihood that individual LNAAs will enter the CNS, even when they are administered in the fasting state.

Finally, consideration should be given to the frequency of AA administration. Sustained high plasma levels of a supplemented AA may result in hepatic induction of AA catabolic enzymes (Harper et al., 1970), thereby minimizing the impact of supplementation. Intermittent dosing schedules may have to be developed to circumvent an increase in AA catabolism.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

TABLE 14–2 Effect of Chronic Dietary Protein Level on the Response of Brain Tryptophan Levels to Tryptophan Administration*

Dietary Protein Level (percent)

Brain Tryptophan Levels (µg/g) after the Administration of the Following Dose of Tryptophan (mg/kg of body weight)

0

25

50

75

100

12

5.4±0.5

18.8±0.7§

35.2±2.0"

64.1±4.3#

59.0±5.4#

40

5.9±0.6

14.2±0.7‡§

18.2±1.1§

33.9±3.2"

44.9±4.3#

* Rats were fed either 12 or 40 percent casein diets for 15–16 days and received intraperitoneal injections of tryptophan 8 h after ingestion of the last meal. Brain tryptophan levels were measured 60 min after peripheral tryptophan administration.

†Data are means±standard errors of the means (n=6/dose). Values in the same row not sharing the same superscripts are significantly different (P<0.05). Data adapted from Shwery (1989).

SUMMARY AND CONCLUSIONS

There is evidence that the protein requirements of endurance athletes may be increased, thereby suggesting that the chronic physical demands of combat situations may increase the protein requirements of military personnel. However, if energy needs are met in the individual, the increase in protein consumption associated with increased food intake will more than meet the protein requirements of the individual. More realistic, however, is a situation in which food intake is decreased under combat situations because of a number of adverse physical and psychologic conditions. Although an energy deficit may not be associated with diminished performance of physically demanding tasks, the impact of an energy deficit on other indices of performance, including cognitive performance, is not well understood.

Provision of meals high in either protein or CHO may influence satiety and certain aspects of mood and performance. However, this effect of meal composition is variable and can be influenced by the age and gender of the individual. Furthermore, the impact of altering meal composition on mood and behavior has not been examined under stressful situations simulating combat. Thus, further studies are warranted prior to assessing the usefulness of this approach.

Supplementation with certain AAs, notably TYR and BCAAs, may play a useful role under stressful conditions; however, studies on the BCAAs are very preliminary in nature. Further studies on TYR are warranted, as its

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

effectiveness has been indicated under circumstances simulating certain aspects of combat situations.

The chronic diet of an individual will influence his or her response to supplemental AAs, especially if the effect is mediated by the CNS. This impact of chronic diet is secondary to changes in plasma AA levels and competition at the blood-brain barrier for uptake into the CNS.

Finally, to maximize and maintain the effectiveness of supplemental AAs, they should not be administered with meals and should be provided on an intermittent basis. Consumption of protein-containing foods in combination with the supplemented AAs may not produce the desired change in plasma AA profiles, especially if CNS uptake of the supplemented AAs is desired. Furthermore, continued elevated plasma levels of the supplemented AAs may result in induction of its catabolic enzymes. Hence, intermittent dosing schedules should be developed to circumvent this.

REFERENCES

Anderson G.H., and E.T.S.Li 1987 Protein and amino acids in the regulation of quantitative and qualitative aspects of food intake. Int. J. Obes. 11(suppl. 3):97–108.


Barkeling, B., S.Rossner, and H.Bjorvell 1990 Effects of a high-protein meal (meat) and a high-carbohydrate meal (vegetarian) on satiety measured by automated computerized monitoring of subsequent food intake, motivation to eat and food preferences. Int. J. Obes. 14:743–751.

Blomstrand E., P.Hassmen, B.Ekblom, and E.A.Newsholme 1991 Administration of branched-chain amino acids during sustained exercise-effects on performance and on plasma concentration of some amino acids. Eur. J. Appl. Physiol. 63:83–88.


Deijen J.B., M.L.Heemstra, and J.F.Orlebeke 1989 Dietary effects on mood and performance. J. Psychiatr. Res. 23:275–283.

Diaz E., G.R.Goldberg, M.Taylor, J.M.Savage, D.Sellen, W.A.Coward, and A.M.Prentice 1991 Effects of dietary supplements on work performance in Gambian laborers. Am. J. Clin. Nutr. 53:803–811.


Federation of the American Societies for Experimental Biology, Life Sciences Research Office 1992 Safety of amino acids used as dietary supplements. Center for Food Safety and Applied Nutrition. FDA Contract No. 223–88–2124, Task No. 8.

Food and Agriculture Organization of the United Nations/World Health Organization/United Nations University 1985 Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Geneva, WHO Technical Report Series No. 724. Geneva: World Health Organization.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

Glanville N.T., and G.H.Anderson 1985 The effect of insulin deficiency, dietary protein intake and plasma amino acids on brain amino acid levels in rats. Can. J. Physiol. Pharmacol. 10:603–610.


Harper A.E., N.J.Benevenga, and R.M.Wohlhueter 1970 Effects of ingestion of disproportionate amounts of amino acids. Physiol. Rev. 50:428–558.

Health and Welfare, Canada 1990a Nutrition Recommendations: The Report of the Scientific Review Committee. Ottawa, Ontario, Canada: Supply and Services Canada.

1990b Report of the Expert Advisory Committee on Amino Acids. Ottawa, Ontario, Canada: Drugs Directorate, Health Protection Branch, Department of National Health and Welfare.

Henriksson, J. 1991 Effect of exercise on amino acid concentrations in skeletal muscle and plasma. J. Exp. Biol. 160:149–165.


Li, E.T.S., and G.H.Anderson 1982 Meal composition influences subsequent food selection in the young rat. Physiol. Behav. 29:779–783.


National Research Council 1980 Recommended Dietary Allowances, 9th ed. Report of the Food and Nutrition Board, Committion on Life Sciences, Washington, D.C.: National Academy Press.

1985 Nutrient Adequacy: Assessment Using Food Consumption Surveys. Report of the Subcommittee on Criteria of Dietary Evaluation, Food and Nutrition Board, Commission on Life Sciences, National Research Council. Washington, D.C.: National Academy Press.


Peters J.C., and A.E.Harper 1985 Adaptation of rats to diets containing different levels of protein: Effects on food intake, plasma and brain amino acid concentrations and brain neurotransmitter metabolism. J. Nutr. 115:382–398.


Shwery, M.M. 1989 Effect of Chronic Dietary Protein Concentration on the Neurochemical Response to Tryptophan Administration. M.Sc. Thesis. University of Toronto, Toronto, Ontario, Canada.

Smoak B.L., A.Singh, B.A.Day, J.P.Morton, S.B.Kyle, S.J.Pepper, and P.A.Deuster 1988 Changes in nutrient intakes of conditioned men during a 5-day period of increased physical activity and other stresses. Eur. J. Appl. Physiol. 58:245–251.

Spring B., O.Maller, J.Wurtman, L.Digman, and L.Cozolino 1982-1983 Effects of protein and carbohydrate meals on mood and performance: Interactions with sex and age. J. Psychiatric Res. 17:155–167.

Spring B., J.Chiodo, M.Harden, M.J.Bourgeois, J.D.Mason, and L.Lutherer 1989 Psychobiological effects of carbohydrates. J. Clin. Psychiatry 50 (Suppl.):27–33.


Tarnopolsky M.A., J.D.MacDougall, and S.A.Atkinson 1988 Influence of protein intake and training status on nitrogen balance and lean body mass. J. Appl. Physiol. 64:187–193.

Tarnopolsky M.A., S.A.Atkinson, J.D.MacDougall, B.B.Senor, P.W.R.Lemon, and H. Schwarcz 1991 Whole body leucine metabolism during and after resistance exercise in fed humans. Med. Sci. Sports Exerc. 23:326–333.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

Wagenmakers A.J., J.H.Brookes, J.H.Coakley, T.Reilly, and R.H.Edwards 1989 Exercise-induced activation of the branched-chain 2-oxo acid dehydrogenase in human muscle. Eur. J. App. Physiol. 59:159–167.

Wurtman R.J., F.Hefti, and E.Melamed 1981 Precursor control of neurotransmitter synthesis. Pharmacol. Rev. 32:315–335.

DISCUSSION

JOHN MILNER: I have a couple of comments. First, with regard to the toxicity studies that have been done, a lot of those old studies by Jessie Greenstein and others showed that for simultaneous supplementations of arginine, you might want to think in terms of that being a scavenger for the toxicity, because a lot of that relates to ammonia. You did not describe at all the effect of nitric oxide as being a regulator of growth hormone, insulin, or glucagon. Did you comment on that? I am not sure that I know that well enough either.

CAROL GREENWOOD: No, someone else is probably a bit more familiar with that.

GILBERT LEVEILLE: Carol Greenwood, on one of your slides toward the end where you were looking at tryptophan, it seemed like you reached the maximum at 75 mg/kg or whatever it was. Is that the case? There was no statistical difference between the last two treatments.

CAROL GREENWOOD: You are quite right, when you look at the data for animals fed in the low protein diet, brain TRP levels were identical when both 75 and 100 mg/kg of TRP were administered intraperitoneally. This, however was not the case for animals fed the high protein diet where changes in brain TRP were observed across all doses of TRP administered. On first observation, it may suggest that with the lower protein diet, the brain uptake carrier was saturated with 75 mg/kg TRP and hence higher TRP doses would not be effective in further increasing brain TRP levels. This could be consistent with any carrier-mediated process. Nevertheless, we have not reproduced this observation and hence it would not be appropriate to draw any firm conclusions at this time.

WILLIAM BEISEL: I know that when you use arginine and a number of other amino acids you can get hormone responses. I have seen no strong data that show when you give them orally that you get these responses. From tests we have done in our lab, we cannot show any responses with high levels of amino acids with supplements and the growth hormone process.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

CAROL GREENWOOD: I know that arginine is a powerful secretagogue for a variety of hormones, including growth hormone. Indeed it can be used clinically as a test for pituitary function. Neverthless, you must remember that in these clinical tests, arginine is given on an acute basis. It would not be surprising that with chronic exposure to arginine that its catabolism would be increased so that in the long term, circulating arginine levels would be within a normal range and that chronic arginine feeding or administration would not result in chronic elevations in plasma hormone levels. Thus it may not be surprising that you do not see an effect with chronic AA treatment.

JOHN IVY: In looking at these data, I am always puzzled with high-protein diets, particularly in studies done in rats. This was done under conditions of adequate hydration.

CAROL GREENWOOD: Yes.

EDWARD HORTON: In situations like feeding military troops, you always have a relative state of dehydration. Has anyone looked at the relative impact of water availability in these kinds of studies, particularly the high-protein diets or high/amino/acid supplementation?

CAROL GREENWOOD: I do not know of any studies looking specifically at compensatory changes in water intake in association with chronic feeding of high protein diets. This is a very important point, particularly in reference to the combat situation where water availability may be severly limited. Nevertheless, there have been numerous studies examining changes in water consumption in association with AA supplementation. For example, studies in Harvey Anderson’s laboratory in which they were looking at different mixtures of AA demonstrate that some, but not all, AA stimulate water intake when water availability is unlimited. These studies, however, examined the effect of acute administration of AA and the demands for additional fluid intake to allow for appropriate volumes of urine excretion when AA are administered chronically has not been examined to the best of my knowledge. This may indeed represent a contra-indication for AA supplementation especially in desert-like conditions where adequate hydration is already a problem.

WILLIAM BEISEL: During certain stresses with muscle, there is a breakdown and a release of amino acids. Does that sort of thing happen when somebody takes a large amount of tryptophan?

CAROL GREENWOOD: Yes, it does. You see tryptophan being metabolized by alternate pathways. You also see those kinds of things happening normally

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

with hormone fluctuations in women associated with menstrual cycle activity, so we do see activation of those types of pathways, although I think the important thing that perhaps philosophically has not been addressed is that we have been talking a lot in terms of looking at carbohydrate supplementation associated with exercise. Yet, I think it is clear that, no matter what you are going to do, you are also going to get a lot of things occurring during that period and that, presumably, the amino acids are providing a skeleton in terms of that glucose.

We have not talked at all about the need for protein to replenish those amino acids that were metabolized during that exercise period, so that while the strategy may still indeed be appropriate of looking at carbohydrate loading to support the exercising time, one looks, in terms of replenishment, at the end of it not only in terms of water and electrolytes but perhaps also proteins in general or mixtures of amino acids in particular. Those would be the precursors that one would predict during that period, and that would be a time that would be more appropriate for a supplement.

JOHN IVY: I do not believe that as long as you have sufficient carbohydrates, for instance, amino acids are going to be used very much.

CAROL GREENWOOD: I agree with you in terms of providing optimal nutrients to the muscle during a bout of exercise in an adequately nourished individual. However, I think that when you look at an individual under a chronic stressful situation, that you also need to consider the impact of chronic demands. As stated before, it is highly likely that individuals in the combat situation will not be consuming adequate calories to meet their individuals in the combat situation will not be consuming adequate calories to meet their energy demands and that they will be experiencing repeated periods of prolonged exercise. Under these circumstances, AA may become important energy substrates to the muscle and it may be important to determine whether gucogenic AA have been depleted under these circumstances and whether repleting the AA pool is necessary.

JOHN IVY: I think the major glucogenic precursors during exercise is lactate coming ultimately from breakdown.

EDWARD HORTON: I think this is a very important area. Just to add to what John is saying, I did not mention it in terms of the changes that are going on during postexercise recovery. John Devlin in our group has really looked at glucose and amino acid metabolism during the first 14 hours of postexercise recovery, and John mentioned that you continue to get lactate output from nonexercising muscles if you do cycle exercise and forearm balance

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×

studies—there is continued lactate output, actually, insulin resistance, in the nonexercising muscles—so that insulin does not stimulate glucose uptake. The lactate appears to be coming from continued glycogen breakdown.

In addition to that, you also get continued alanine output, and so there is amino acid oxidation going on during the postexercise recovery period with continued alanine. So I think your point is very well taken, that we should be providing the substrates for gluconeogenesis and rebuilding glycogen stores after exercise to both carbohydrate and amino acid.

ROBERT NESHEIM: If a person is eating a regular meal following that, it seems to me you are probably taking care of that.

CAROL GREENWOOD: I would guess so. I mean, I think that under an energy replete situation, protein probably is not an issue. However, in a combative situation where the troops are not eating sufficient food, then I think the whole ballpark changes in terms of the questions that one may want to ask.

Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
×
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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Suggested Citation:" 14. Performance-Enhancing Effects of Protein and Amino." Institute of Medicine. 1994. Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/4563.
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The physiological or psychological stresses that employees bring to their workplace affect not only their own performance but that of their co-workers and others. These stresses are often compounded by those of the job itself. Medical personnel, firefighters, police, and military personnel in combat settings--among others--experience highly unpredictable timing and types of stressors.

This book reviews and comments on the performance-enhancing potential of specific food components. It reflects the views of military and non-military scientists from such fields as neuroscience, nutrition, physiology, various medical specialties, and performance psychology on the most up-to-date research available on physical and mental performance enhancement in stressful conditions. Although placed within the context of military tasks, the volume will have wide-reaching implications for individuals in any job setting.

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