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Protein and Amino Acids, 1999

Pp. 1-15. Washington, D.C.

National Academy Press

Executive Summary

As the U.S. military faces the millennium and the changing nature of modern warfare, it must anticipate physical and mental challenges never encountered before. Longer periods of intense physical exertion and possible food deprivation; advanced weaponry requiring maximum attention, precision, and decision-making ability; and greater threats of infection, injury, and exposure to environmental stressors are quickly becoming the reality that soldiers face. Military scientists charged with maintaining and optimizing the health and performance of their personnel are looking to the role that nutrition may play in this process, and have expressed particular interest in the body of current research suggesting the importance of protein and amino acids.

Proteins catalyze virtually all chemical reactions in the body, regulate gene expression, comprise the major structural elements of all cells, regulate the immune system, and form the major constituents of muscle. Individual amino acids, the components of proteins, also serve as neurotransmitters, hormones, and modulators of various physiological processes. Every aspect of physiology involves proteins. The relationships between dietary protein and bodily protein



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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Protein and Amino Acids, 1999 Pp. 1-15. Washington, D.C. National Academy Press Executive Summary As the U.S. military faces the millennium and the changing nature of modern warfare, it must anticipate physical and mental challenges never encountered before. Longer periods of intense physical exertion and possible food deprivation; advanced weaponry requiring maximum attention, precision, and decision-making ability; and greater threats of infection, injury, and exposure to environmental stressors are quickly becoming the reality that soldiers face. Military scientists charged with maintaining and optimizing the health and performance of their personnel are looking to the role that nutrition may play in this process, and have expressed particular interest in the body of current research suggesting the importance of protein and amino acids. Proteins catalyze virtually all chemical reactions in the body, regulate gene expression, comprise the major structural elements of all cells, regulate the immune system, and form the major constituents of muscle. Individual amino acids, the components of proteins, also serve as neurotransmitters, hormones, and modulators of various physiological processes. Every aspect of physiology involves proteins. The relationships between dietary protein and bodily protein

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance metabolism are a major focus of research. Many questions remain regarding the validity of methods for assessment of protein balance; thus, the question of how best to assess dietary protein requirements remains unanswered. In addition, the influences of genetic factors, hormones, physical activity, injury and infectious processes, and environmental stresses on protein metabolism and protein requirements continue to be explored. Another major focus of research is the role of protein and amine acid balance in modulating physiological function and behavior, as measured for example by physical and mental performance. The possibility that protein or individual amine acids in quantities that exceed those required to maintain protein balance may have the potential to contribute to performance optimization is of great interest. COMMITTEE'S TASK In 1992, the Committee on Military Nutrition Research (CMNR) was asked by the Military Nutrition Division of the U.S. Army Research Institute of Environmental Medicine to conduct an investigation into the fate of a group of soldiers in special forces training. The committee found that these soldiers lost significant amounts of muscle mass during the training period and recommended changes in their intakes of energy and protein. In 1994, the CMNR was asked to conduct a workshop and prepare a report on the performance-enhancing potential of individual food components. The committee recommended further research on the ability of the amine acid tyrosine to enhance several measures of cognitive performance in stressful situations. The CMNR conducted a similar workshop in 1996 to examine the influence of dietary factors, including protein and amine acids, on immune function. Finally, in 1997, the CMNR was asked by the U.S. Army Medical Research and Materiel Command to update its earlier findings and to conduct a workshop on the potential role of protein and amine acids in maintaining and enhancing the physical and cognitive performance of soldiers. Specifically, the committee was asked to respond to three questions: Do protein requirements increase with military operational stressors, including high workload with or without energy deficit? Are there gender differences in protein requirements in endurance exercise? What is the optimal protein content (and protein-energy ratio) for standard operational rations, and specifically, is the Military Recommended Dietary Allowance (MRDA) for operational rations (100 g/d for men and 80 g/d for women) appropriate? Is the protein MRDA for women appropriate during pregnancy and lactation? Is there evidence that supplementation with specific amine acids (AAs) or modification of dietary protein quality would optimize military performance, either cognitive or physical, during high workload, psycho-

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance logical stress, or energy deficit? What are the risks of amino acid supplements and high-protein diets? METHODS In considering the questions posed by the Army, the CMNR collaborated with the Subcommittee on Body Composition, Nutrition, and Health of Military Women. The two committees convened a workshop in March 1997, in Washington, D.C., to bring together experts in protein metabolism, exercise physiology, and cognitive psychology, as well as military nutritionists familiar with historical and recently completed nutritional assessment surveys. Each of the workshop speakers was asked to prepare a review paper. After the workshop, the committees summarized the presentations, and drawing upon their summaries of the workshop, the commissioned papers, background materials provided by the speakers, focused literature searches by the staff, and their own expertise in the field of protein metabolism, they prepared an overview of the pertinent issues, responses to the sponsor's questions, conclusions, and recommendations. These form chapters 1 and 2 of this report. The authored papers, which can be found in Chapters 3 through 16, were not subject to review. FINDINGS Effect of Stressors on Protein Requirements of Military Personnel Baseline Protein and Amino Acid Requirements Current estimates of protein and amino acid requirements are based on studies employing the technique of nitrogen balance assessment. A 1985 report of the Food and Agriculture Organization, in collaboration with the World Health Organization and the United Nations University (FAO/WHO/UNU, 1985) proposed a protein requirement of 0.625 g per kilogram of body weight per day (g/kg BW/d) for egg or beef protein, so-called high-quality proteins. The current recommended dietary allowance (RDA) for protein in the U.S. diet is 0.8 g/kg BW/d for adults (Table ES-1; NRC, 1989). Consensus exists for the current adult protein requirement but not the adult requirement for total essential (indispensable) amino acids (IAAs). Based on nitrogen balance data, the recommendation for IAAs as a percentage of total protein intake is 43 percent for children and only 11 percent for adults (FAO/WHO/UNU, 1985). Since the 1985 report, Young and colleagues have presented data showing that the FAO/WHO/UNU pattern cannot maintain

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance TABLE ES-1 Recommended Dietary Allowances for Protein Age (years) or Condition Weight (kg) RDA g/d RDA g/kg BW/d Males 19—24 72 58 0.8 25-50. 79 63 0.8 51+ 77 63 0.8 Females 19-24 58 46 0.8 25-50 63 50 0.8 51+ 65 50 0.8 Pregnant   60   Lactating (first 6 months)   65   Lactating (second 6 months)   62     SOURCE: Adapted from NRC (1989). amine acid homeostasis. From these data they conclude that the adult IAA requirement is 31 percent of the total protein requirement, approximately 3 times the FAO/WHO/UNU estimate (Marchini et al., 1993; see also Young, Chapter 10). The importance of this debate lies in the definition of dietary protein quality, which is an assessment of the efficiency of protein utilization, determined in part by how closely the IAA content of a given protein resembles an IAA scoring pattern for the age group in question. The scoring pattern is based on the estimated IAA requirements for that age group. If the 1985 FAO/WHO/UNU estimate of adult IAA requirements is correct, protein quality is no longer an issue for adults, either here in the United States or worldwide. Young's hypothesis regarding adult IAA requirements is based on estimations of obligatory indispensable amine acid oxidation computed from obligatory nitrogen (N) losses and studies of amine acid oxidation using stable isotopically labeled amine acid infusion. This hypothesis has been challenged most persistently by Millward (1994; see also Chapter 9). Millward's assertion that Young's data are flawed is based on several arguments, the most serious of which are that the amount of tracer infused in Young's experiments was great enough to alter amine acid balance significantly and that the true precursor amine acid enrichment was not measured accurately. In addition, Millward argues that the real metabolic demand for IAA is based only on net protein synthesis, not turnover. There is also disagreement on the nutritional status of subjects in previous studies that assessed protein and AA requirements and the need to employ subjects who have adapted to the experimental protein intake. The practical implications of the debate between Millward and Young center around the requirements for the IAA lysine. The lysine content of cereal grain proteins, which are considered low-quality proteins, is too low to support

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance the growth of infants. However, if Millward is correct in his assessment of IAA requirements, all dietary proteins, whether animal or plant in origin, contain enough lysine to provide adequate amino acids to adults if these proteins are consumed in quantities that meet overall protein requirements. Both Millward and Young agree that further experiments are necessary to clarify adult IAA requirements. Physical Activity Despite a commonly held belief that athletes, particularly body builders, have greater requirements for dietary protein than sedentary individuals, the evidence in support of this contention is controversial. A major function of amino acids in muscle during exercise is to supply intermediates to the tricarboxylic acid (TCA) cycle so that the energy needs of the contractile apparatus of the muscle are met. The extent of this amino acid oxidation depends on exercise intensity, nutritional status (energy stores), training status, and gender. However, it is not clear that the magnitude of this amino acid oxidation is sufficient either to increase whole-body protein requirements when energy intake matches output or to warrant increasing the MRDA for protein. Efforts to investigate the possibility that protein requirements are increased by physical activity have been complicated by several factors. First, increases in protein intake result in increases in the catabolic processes that oxidize amino acids. This adaptation has significant implications for individuals who habitually consume high-protein diets: these individuals may face the risk of significant loss of protein stores if circumstances such as field operations suddenly force them to curtail protein intake. Another factor confounding the effort to examine the influence of physical exertion on protein requirements is the finding that energy deficit results in an increased protein requirement. Finally, a number of studies have suggested that regular moderate physical activity may have a protective effect on protein retention. Some studies have suggested that the protein requirements of athletes may be as high as 2-2.5 g/kg BW/d. The most carefully controlled studies have shown that endurance exercise increases protein requirements in men. However, in male weight lifters, the maintenance of body mass requires no increase over the requirements of sedentary individuals. The small number of studies of physical activity and protein requirements that have included women show that the needs of women appear to be similar to those of men. Thus, the evidence to date suggests that sustained endurance exercise, such as that done by some military personnel, may increase protein requirements over the amounts required by sedentary individuals; however, typical intakes (1.5 g/kg BW/d) are usually well within the range of requirements as long as energy intake is adequate to meet energy expenditure.

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Infection, Injury, and Illness Systemic infections and serious injuries trigger alterations in body protein metabolism that lead to increases in protein requirements. The contractile proteins of skeletal muscles undergo rapid breakdown to supply amino acids for energy and for specific immune responses in the liver and immune tissues. Protein requirements are increased to approximately 1.5 g/kg BW/d in almost all trauma patients except bum patients, whose requirements are elevated to 2-2.5 g/kg BW/d (although treatment advances are slowly lowering these requirements). However, the provision of high levels of protein to severely burned patients fails to induce repletion of muscle protein stores. The administration of anabolic hormones, such as growth hormone, insulin-like growth factor, and testosterone, in conjunction with nutritional support is the subject of considerable research at the present time, and a number of positive studies have been reported indicating accelerated wound healing. However, two recent trials of recombinant human growth hormone administration to postsurgical and posttrauma patients in several intensive care units were discontinued due to higher mortality rates among the treated patients. Other Stressors The influences of temperature extremes and high altitude on protein requirements have been discussed in earlier CMNR reports. Although sweat losses of nitrogen can be considerable, the need for protein does not appear to increase in hot climates. Similarly, protein needs are not increased in cold temperatures. The need to increase fluid intake when consuming a high-protein diet has led to recommendations that excesses in dietary protein intake be avoided in environments where access to drinking water may be a problem. Decreases in lean body mass observed during acclimatization to high altitude appear to be due to the overall decrease in energy intake, rather than to an increased requirement for protein. The effects of combined stressors, such as intense physical activity superimposed on change in climate or altitude, on protein requirements have not been investigated systematically. The MRDA for Protein The current RDA for protein for men and women (the nonmilitary population) is 0.8 g/kg BW/d (see Table ES-1). In comparison, the MRDA for protein is 100 g/d for men and 80 g/d for women. These recommendations are for physically active individuals in temperate climates with energy intakes of 3600 kcal/d for men and 2000-2800 kcal/d for women. Thus, for active-duty men and women of current mean weight 78 kg and 63 kg, respectively, the MRDA is

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance approximately 1.3 g/kg BW/d. The formulation of operational rations is based on the MRDAs. Studies conducted in the 1940s and throughout the past decade have shown that military personnel maintain relatively high protein intakes both in the field and in garrison. Protein intake in the field averages 1.3 g/kg BW/d for men and 1.2 g/kg BW/d for women, exceeding the estimated protein requirement for sedentary individuals and the increased requirement observed by several investigators for athletes. Further, dietary surveys indicate that soldiers in the field preferentially eat the higher-protein components of rations, resulting in mean protein intakes of 86-132 g/d for men and 68-96 g/d for women. Because protein metabolism is influenced by energy intake and expenditure, these factors must be considered in judging the adequacy of soldiers' protein intake. Studies conducted on Ranger trainees revealed that although these soldiers experienced an average daily energy deficit of 1200 kcal (over 8 weeks), protein intake averaged more than 100 g/d. Nevertheless, the loss of lean tissue mass was significant and was inversely proportional to initial body fat stores, suggesting that negative energy balance contributed to this loss. Thus, in the absence of additional data on energy balance, the MRDA for protein and the protein intake of the average soldier appear to be more than adequate. Data are insufficient to establish an ideal protein-energy ratio. Pregnancy and Lactation Currently, there are no MRDAs for pregnancy or lactation. As shown in Table ES-1, the RDA for protein is increased by 10 g/d for pregnant women and 15 g/d for lactating women. The recommended protein intakes for women in the weight range, of 46-63 kg would be 44-57 g/d during pregnancy and 60-72 g/d during lactation. Some studies have suggested that the RDA for protein during lactation is inadequate and have shown that actual protein requirements may be as high as 1.5 g/kg BW/d (69-94 g/d) (Motil et al., 1996). The MRDA of 80 g/d would therefore be sufficient to meet the apparent protein requirements of pregnant or lactating women. Benefits and Risks of Protein and Amino Acid Supplements and Alternative Sources of Dietary Protein Evidence from recent Army surveys suggests that in addition to the high dietary protein intake of the average soldier, many soldiers use protein and amino acid supplements in the belief that these products will improve performance (Warber et al., 1996). In addition, evidence suggests that increasing numbers of soldiers, particularly women, are consuming diets largely or completely lacking in animal products, with the result that dietary protein is

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance increasingly of plant origin. The potential health benefits and risks of protein and amine acid supplements, high-protein diets, and vegetarian diets were considered. Protein and Amino Acid Supplements and Cognitive Performance It has been known for some time that the synthesis in brain of several neurotransmitters (serotonin and the catecholamines, dopamine and norepinephrine) is influenced by the levels of their precursor amine acids (tryptophan and tyrosine, respectively) in the diet. In laboratory animals, the rates of synthesis of these transmitters respond to changes in tryptophan and tyrosine concentrations that occur following single meals, as well as to chronic changes in dietary protein content. Of greatest potential relevance to the military, brain tyrosine and tryptophan concentrations in animals can decrease when protein intake falls below the required level, leading to reductions in synthesis of serotonin and the catecholamines. Under field conditions, which are typically associated with increased physical activity and stress (conditions that stimulate the turnover of serotonin and the catecholamines), such changes may be relevant. Reduced food intake could impede serotonin and catecholamine synthesis at a time when increased amounts of these neurotransmitters may be required to support important cognitive functions. However, relatively little is known about how reduced serotonin synthesis might impede brain function. Serotonin neurons are most active when animals are awake and physically active and are important in channeling sensory information to the brain. Thus, it is possible that some aspects of sensorimotor function might be diminished under conditions of extended energy and protein deprivation. No studies have been conducted to evaluate the possible benefit of protein or tryptophan supplementation under such conditions. Catecholamine neurons increase their activity in response to a variety of stressful conditions and appear to regulate behavioral parameters such as attention and state of arousal. A 1994 CMNR report presented preliminary evidence that tyrosine supplements might improve some types of cognitive performance under stressful conditions and recommended further research to explore the potential value of tyrosine supplements for enhancing soldier performance (IOM, 1994). Only one subsequent study has shown that tyrosine administration appears to restore marksmanship performance degraded by fatigue and cold, but the effects of tyrosine are even less evident under normal circumstances. Thus, although earlier studies appeared to show promise, there have been no more recent studies to reevaluate the earlier findings. There is little evidence at present, therefore, to justify the administration of either tryptophan or tyrosine for the purpose of modifying behavior. Further research is necessary on the behavioral effects of such supplements as well as the effects of meal-related changes in brain serotonin and catecholamines.

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Protein, Amino Acids, Muscle Mass, and Physical Performance Current methods for routine assessment of muscle mass remain inadequate, particularly when applied to the measurement of changes in muscle mass. In addition, the relationship between muscle mass and measures of function such as strength and endurance remains unclear. Strength appears to be related to the synthesis of both myosin heavy chain and the mitochondrial enzyme cytochrome C oxidase. Apparent gender differences in endurance disappear with appropriate adjustment for differences in muscle mass. The impact of dietary protein intake and physical activity on muscle protein synthesis is modulated by the hormones insulin, growth hormone, insulin-like growth factor I (IGF-I), thyroid hormone, cortisol, and particularly testosterone. Testosterone, growth hormone, and IGF-I all stimulate muscle protein synthesis, whereas insulin appears to inhibit protein breakdown. Cortisol, which is secreted in response to stress, stimulates the breakdown of muscle protein, although its mechanisms of action are not precisely known. Although there is considerable research interest in the potential for supplemental protein or amino acids to increase muscle protein synthesis or physical performance, little evidence supports such a role in the absence of anabolic steroids. The ''central fatigue" theory, which hypothesized that the administration of branched-chain amino acids would decrease or delay the central nervous system and muscle fatigue that resulted from increased brain tryptophan, is not supported by evidence. In contrast, a postexercise feeding regimen combining carbohydrate and protein appears to increase the endurance of individuals performing strenuous exercise over several days. Protein, Amino Acids, and Immune Function In addition to the increased requirement for protein in individuals suffering systemic infection or major injury, growing evidence appears to suggest a potentially beneficial role for the amino acid glutamine in modulating immune function. Studies of hospitalized, critically ill patients show that glutamine supplementation of total parenteral nutrition solutions results in increased survival and decreased length of hospital stay (Wilmore et al., 1997a). However, no effect of glutamine supplementation on the parameters of immune function was observed in Special Forces trainees, whose increased rate of infection and depressed immune function may be linked to the high level of physical exertion during training (Shippee et al., 1995). In addition, the influence of glutamine supplementation on infection rate in athletes (the so-called overtraining effects) has not been studied extensively.

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Issues of Protein Quality and Timing of Consumption Considerable debate currently surrounds the requirement of adults for high-quality protein. Consumption of plant proteins such as soy protein or a combination of cereal and legume proteins in place of all or part of the animal protein in the diet, which results in a diet lower in total fat, saturated fat, and cholesterol and higher in soluble fiber and other potentially beneficial substances, has been shown to lower serum cholesterol and triglyceride levels. Among the plant proteins, soy protein has a balance of amino acids that most closely resembles that of animal proteins, and substitution of this protein in rations would not markedly decrease their nutritional value. However, the taste might be affected; thus, product development and testing are required to ensure the acceptance of soy products in rations. As mentioned above, research suggests that protein and carbohydrate meals consumed shortly after exercise may improve glycogen storage and maintenance of lean mass, resulting in increased endurance on subsequent days. Dietary Protein and Renal Function Chronic high levels of dietary protein have been associated with decline in renal function in aging individuals; however the evidence is not sufficient to conclude that dietary protein itself is the causative factor. In contrast, high-protein diets can stimulate nephrolithiasis (kidney stone formation) in otherwise healthy individuals. Because a restriction of fluid intake can increase the likelihood of stone formation, deployed military personnel are at especially high risk if water supplies are inadequate. Dietary Protein and Calcium Status The potential calciuretic effect of high-protein diets has been recognized for some time in men and women. For each 50 g increment in dietary protein, an estimated 60 mg additional urinary calcium is lost. This loss may be modulated by other dietary factors such as phosphorus. At present, there is limited evidence to suggest that high dietary protein intake may be a risk factor for osteoporosis. Calcium balance appears to remain close to equilibrium with protein intakes up to 74 g/d and calcium intakes of 500-1400 mg/d. In addition, there is evidence to suggest that regular weight-bearing physical activity contributes to bone strength. Thus, protein intake would not appear to be a major risk factor for calcium loss in the average military woman.

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Amino Acid Toxicity The risk of deleterious interactions between pharmacological doses of single amino acid supplements and over-the-counter or prescription medications may be considerable. In addition, supplement purity is a major consideration, as demonstrated by the harm that resulted from widespread use of tryptophan supplements that were later believed to have contained a low-level contaminant. Lack of safety data on the consumption of high levels of individual amino acids by normal, healthy individuals suggests that their use be limited until further research is performed. Protein and Amino Acid Supplements and Pregnancy Evidence from a major nutritional supplementation study suggests that the use of high-protein supplements (to achieve a protein intake that represents 34 percent of the total daily energy intake, in contrast to the more usual 11-14 percent) may be harmful to fetal development. Studies in laboratory animals suggest that supplementation of the diet with single amino acids also may be dangerous to the developing fetus. CONCLUSIONS AND RECOMMENDATIONS Effects of Stressors on Protein Requirements At the present time, considerable controversy exists regarding the validity of estimations of protein and amino acid requirements. In addition, the evidence is insufficient to conclude that high levels of physical activity increase protein requirements for individuals whose energy intake matches their output. Continuous excessive intake of protein may cause increased protein catabolism, resulting in greater risk of negative protein balance when protein intake is reduced. As emphasized in earlier IOM reports (IOM, 1992, 1995), the importance of adequate energy intake (sufficient to match output and to avoid weight loss) and protein intake should he emphasized to soldiers as the primary means of maintaining lean tissue mass. Research is needed to resolve the controversy regarding the adult requirement for indispensable amino acids and to quantitate more precisely the effect of energy deficit on protein and indispensable amino acid requirements.

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance Systemic infections and serious injuries clearly increase protein requirements. However data suggest that in patients recovering from burns, the elevation of dietary protein intake alone does not permit the recovery of muscle mass to begin immediately, because of the development of the acute phase response, which is accompanied by changes in hormonal status. Research on the effects of treatment with anabolic hormones is ongoing. Military researchers and physicians should pay careful attention to civilian research on the effects of treatment with anabolic hormones on recovery from burns and other injuries. Where appropriate, military-specific models should be developed. Military Recommended Dietary Allowances for Protein Without more data on the functional implications of varying protein intakes, it is not possible to define with accuracy the optimal protein content of standard operational rations. However, based on currently available data, the use of the MRDA for operational rations is appropriate and provides a generous level of protein intake. The MRDA covers the protein requirements of pregnant and lactating women. Current MRDAs for protein should be maintained. Provided that energy intake is adequate, no increase in MRDAs is necessary for pregnant or lactating women. Benefits and Risks of Supplemental Protein, Amine Acids, and Alternative Sources of Dietary Protein Research fails to support the use of protein supplements to facilitate muscle building under conditions of adequate energy and protein intake. Given adequate nutritional intake, soldiers should not use protein supplements for muscle building. Military researchers and physicians should pay careful attention to civilian research on the use of anabolic hormones to increase muscle or lean tissue mass. At the present time, considerable debate surrounds the adult requirement for indispensable amine acids and thus high-quality proteins. Protein supplied in operational rations should be of high quality and digestibility. Energy intakes should be adequate, and sources

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance of energy should be consumed within 2 h of an intense bout of endurance exercise, to replace depleted muscle glycogen. There is a lack of safety data on the consumption of high levels of individual amino acids by normal, healthy individuals. Furthermore, research supporting the use of tyrosine supplements to enhance cognitive performance under field conditions is inconclusive. Single amino acid supplements should not be used to modify cognitive performance, due to potential toxicity and insufficient evidence of efficacy. Supplemental glutamine and arginine have yet to show conclusively beneficial effects on immune function. The MRDA, if consumed, provides adequate protein and energy to sustain immune function under normal field conditions. The military should test the ability of supplemental glutamine and arginine to enhance the immune response and decrease rates of infection under field conditions and in seriously injured hospitalized patients. Current intakes of protein among military populations are high and show no apparent harmful effects, provided fluid intake is adequate. There is no evidence of increased health risks from a high intake of dietary protein; however, an amino acid imbalance may be created with use of single amino acid or protein supplements. Although no data are available from groups similar in age and fitness characteristics to military personnel, a review of the information available shows that high protein intake is not associated with direct effects on renal dysfunction. However, high-protein diets may indirectly stimulate renal stone formation and result in an increased renal workload, due to the need to concentrate urine. High protein intake has been shown to increase urinary calcium loss, but there is no definitive evidence that the level of protein intake observed in Army women in field conditions represents a risk factor for osteoporosis. Given the high protein content of operational rations, adequate fluid intake should be emphasized, as recommended by the "Fluid Doctrine" (IOM, 1994).

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance BOXES-1 Major Recommendations As recommended in earlier IOM reports (IOM, 1992, 1995), the importance of adequate nutrient intake (with sufficient energy to match output and to avoid weight loss) should be emphasized to soldiers as the primary means of maintaining lean tissue mass. Given adequate nutritional intake, soldiers should not use protein supplements for muscle building. Single amino acid supplements Should not be used to modify cognitive performance, due to potential toxicity and insufficient evidence of efficacy. Current MRDAs for protein should be maintained. Provided that energy intake is adequate, no increase in MRDAs is necessary for pregnant or lactating women. Protein supplied in operational rations should be of high quality and digestibility. Energy intakes should be adequate, and source of energy should be consumed within 2 h of an intense bout of endurance exercise, to replace depleted muscle glycogen. Military researchers and physicians should pay careful attention to civilian research on the effects of treatment with anabolic hormones on recovery from bums and other injuries. Where appropriate, military-specific models should be developed. The military should test the ability of Supplemental glutamine and arginine to enhance the immune response and decrease rates of in-faction under field conditions and in seriously injured hospitalized patients. Given the high protein content of operational rations, adequate fluid intake should be emphasized, as recommended by the Fluid Doctrine (IOM, 1994).

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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance REFERENCES FAO/WHO/UNU (Food and Agriculture Organization of the United Nations/World Health Organization/United Nations University). 1985. Energy and protein requirements. Report of a joint expert consultation. World Health Organization Technical Report Series No. 724. Geneva: World Health Organization. IOM (Institute of Medicine). 1992. A Nutritional Assessment of U.S. Army Ranger Training Class 11/91. March 23. Washington, D.C.: National Academy Press. IOM. 1994. Food Components to Enhance Performance, An Evaluation of Potential Peformance-Enhancing Food Components for Operational Rations, B.M. Marriott, ed. Washington, D.C.: National Academy Press. IOM. 1995. Not Eating Enough, Overcoming Underconsumption of Military Operational Rations, B.M. Marriott, ed. Washington, D.C.: National Academy Press. Marchini, J.S., J. Cortiella, T. Hiramatsu, T.E. Chapman, and V.R. Young. 1993. Requirements for indispensable amino acids in adult humans: Longer term amino acid kinetic study with support for the adequacy of the Massachusetts Institute of Technology amino acid requirement pattern. Am. J. Clin. Nutr. 58:670-683. Millward, D.J. 1994. Can we define indispensable amino acid requirements and assess protein quality in adults? J. Nutr. 124:1509S-1516S. Motil, K.J., T.A. Davis, C.M. Montandon, W.W. Wong, and P.D. Klein. 1996. Whole-body protein turnover in the fed state is reduced in response to dietary protein restriction in lactating women. Am. J. Clin. Nutr. 64:32-39. NRC (National Research Council). 1989. Recommended Dietary Allowances, 10th ed. Washington, D.C.: National Academy Press. Shippee, R.L., S. Wood, P. Anderson, T.R. Kramer, M. Neita, and K. Wolcott. 1995. Effects of glutamine supplementation on immunological responses of soldiers during the Special Forces Assessment and Selection Course [abstract]. FASEB J. 9:731. Warber, J.P., F.M. Kramer, S.M. McGraw, L.L. Lesher, W. Johnson, and A.D. Cline. 1996. The Army Food and Nutrition Survey, 1995-97. Technical Report. Natick, Mass.: U.S. Army Research Institute of Environmental Medicine. Wilmore, D.W. 1997a. Glutamine saves lives! What does it mean? Nutrition 13(4):375-376.

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