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The Role of Protein and Amino Acids in Sustaining and Enhancing Performance

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 metabolism are a major focus of research. 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.

The request for this review originated with scientists at USARIEM who were concerned about the unique nutritional demands placed on soldiers during combat. They were particularly concerned about the role that dietary protein may play in controlling muscle mass and strength, response to injury and infection, and cognitive performance.



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--> The Role of Protein and Amino Acids in Sustaining and Enhancing Performance 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 metabolism are a major focus of research. 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. The request for this review originated with scientists at USARIEM who were concerned about the unique nutritional demands placed on soldiers during combat. They were particularly concerned about the role that dietary protein may play in controlling muscle mass and strength, response to injury and infection, and cognitive performance.

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--> Several previous CMNR reports have focused on issues of protein nutriture and performance. In 1992, the CMNR noted in an evaluation of Army Ranger training that trainees experienced significant loss of muscle mass during periods of intense physical exertion (IOM, 1992b). A follow-up report (IOM, 1993b) found that increases in energy intake only partially prevented such losses. The report Food Components to Enhance Performance (IOM, 1994b) briefly considered the influences of protein and amino acids on physical and cognitive performance and response to stress. The most recent CMNR report, Military Strategies for Sustainment of Nutrition and Immune Function in the Field (IOM, 1999), considered the effects of diet, including protein and individual amino acids such as glutamine, on immune response. This report looks further into the many questions regarding the optimal level of protein intake in a high-stress field environment. How to measure protein balance and estimate protein requirements accurately; how these requirements are affected by physical activity, gender, hormonal factors, and stress; and whether muscle function and cognition are influenced by protein intake and by individual amino acids are all active areas of research. The CMNR decided that the best way to review the state of knowledge in this area was through a workshop. The purpose of this workshop was to bring together leading scientists in the field of protein metabolism to seek their assessment of the current state of knowledge and to determine, based on these assessments, on a careful reading of the literature, and on the expertise of the committee members themselves, whether the recommended intakes of protein or individual amino acids for soldiers should be modified. In May 1996, CMNR and USARIEM personnel met to frame a series of questions, outline the workshop, and identify qualified speakers. A follow-up planning meeting was held in January 1997 and included several members of the Subcommittee on Body Composition, Nutrition, and Health of Military Women. Invited workshop speakers were asked to prepare a paper for presentation and publication that described the key issues of protein metabolism. USARIEM scientists also participated in the workshop, which resulted in a well-rounded group. At the one-day workshop, held in Washington, D.C. on March 13, 1997, each speaker gave a formal presentation, which was followed by questions and a brief discussion period. The proceedings were tape recorded and professionally transcribed. At the end of each group of presentations, a general discussion of the overall topic was held. Immediately after the workshop, the CMNR met in executive session to review the issues, to draft summaries of the presentations, and to provide responses to the sponsor's task questions. Committee members subsequently met with staff in June 1997 and worked separately and together using the authored papers, additional reference materials provided by the staff through limited literature searches, and personal expertise and experience to draft the overview, summary, conclusions, and recommendations.

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--> The principal questions that the CMNR and BCNH (and in turn, the speakers) were asked to address were: Do protein requirements increase with military operational stressors, including high workload and/or energy deficit? What is the optimal protein content (protein to energy ratio) for standard operational rations and, specifically, is the Military Recommended Dietary Allowance (MRDA) for protein in 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 amino acids (AA) would optimize military performance (cognitive function) during high workload, psychological stress, and/or energy deficit? (See summaries of speakers) Is there a risk of using specific AA supplements during pregnancy, especially the first trimester (i.e., organogenesis)? Are there gender differences in protein requirements in endurance exercise, and if so, what might their implications be for performance in military operations? What is the evidence, if any, that protein facilitates muscle building? The committees met after the workshop in executive session, as indicated above, to draft initial responses to these questions, as well as eight additional subquestions that both the CMNR and BCNH felt needed to be addressed. Conclusions and Recommendations As recommended in earlier IOM reports (IOM, 1992a, 1995a), 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. 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. Current MRDAs for protein should be maintained. Provided that energy intake is adequate, no increase in MRDAs is necessary for pregnant or. lactating women. Given adequate nutritional intake, soldiers should not use protein supplements for muscle building. Protein supplied in operational rations should be of high quality and digestibility.

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--> Energy intakes should be adequate, and a source of energy should be consumed within 2 h of an intense bout of endurance exercise, to replace depleted muscle glycogen. Single amino acid supplements should not be used to modify cognitive performance, due to potential toxicity and insufficient evidence of efficacy. 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. Given the high protein content of operational rations, adequate fluid intake should be emphasized, as recommended by the Fluid Doctrine (IOM, 1994). <><><><><><><><><><><><> The committee's responses to the questions, conclusions, and recommendations from this report are included in Appendix M.