Protein and Amino Acids, 1999
Pp. 77-81, Washington, D.C.
National Academy Press
Responses to Questions, Conclusions, and Recommendations
In this chapter, responses are provided to the questions raised by the Army. These responses are based on the material presented in Chapter 1 and form the conclusions drawn by the committee on which its recommendations are based.
1. 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?
At the present time, controversy exists regarding the validity of recent estimations of protein and amino acid requirements (particularly the latter) for adults, a controversy that is based on methodological questions.
In addition, the evidence that high levels of physical activity increase protein requirements for individuals whose energy intake matches their output is equivocal. There is clear evidence that moderate physical activity increases the efficiency of protein utilization. However, strenuous endurance-type exercise has been shown to increase protein requirements above the recommended dietary allowance (RDA), but not the Military Recommended Dietary Allowance (MRDA). In contrast, resistance exercise does not appear to increase the requirement for maintenance of lean mass, although the protein intake that would be required for active individuals to increase tissue mass (1.2-1.5 g/kg BW/d) may be higher than that for sedentary individuals. There is also strong evidence that the efficiency of protein utilization is decreased (and the requirements increased) by a state of negative energy balance.
However, much of the research on the effects of physical activity on protein requirements and the effects of altered protein intakes on performance is difficult to interpret because of the time required for the body to adapt to changes in protein intake. One implication of this adaptation that is of concern for service personnel is that continuous excessive intake of protein may cause increased protein catabolism, resulting in greater risk when protein intake is reduced.
Systemic infection and serious injuries clearly increase protein requirements. However, data suggest that in patients recovering from burns or any major trauma, an increase in dietary protein intake does not permit the recovery of muscle mass to begin immediately, due to the acute-phase response, which is accompanied by changes in hormonal status. Longer term studies are therefore needed during recovery periods. Research on the effects of treatment with anabolic hormones, which stimulate protein synthesis or decrease protein breakdown, is ongoing.
Results of studies of protein requirements in hot, cold, and high-altitude environments suggest that these conditions do not increase protein requirements beyond currently recommended levels. In addition, because increases in protein intake also increase fluid requirements and sources of fluid for drinking are often limited during operations in extreme environments, previous reports of the Committee on Military Nutrition Research (CMNR) have cautioned against excessive protein intake under such circumstances.
The effects of combined stressors and other factors such as emotional stress on protein requirements have not been documented.
As emphasized in earlier IOM reports (IOM, 1992, 1995), the importance of adequate energy intake (sufficient to match output and avoid weight loss) and protein intake should be 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.
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.
2. What is the optimal protein content (and protein-energy ratio) for standard operational rations, and specifically, is the protein Military Recommended Dietary Allowance 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?
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.
3. Is there evidence that supplementation with specific amino acids (AAs) or modification of dietary protein quality would optimize military performance, either cognitive or physical, during high workload, psychological stress, or energy deficit. What are the risks of amino acid supplements and high-protein diets?
At the present time, considerable debate surrounds the adult requirement for indispensable amino acids and thus high-quality proteins. Research fails to support the use of protein supplements to facilitate muscle building or improve physical performance under conditions of adequate energy and protein intake. In addition, research supporting the use of tyrosine supplements to enhance cognitive performance under field conditions is inconclusive. 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. Furthermore, with the exception of tryptophan, commercial preparations of which have been
documented to cause specific toxic effects, there is a lack of safety data on the consumption of high levels of individual amine acids.
Some plant proteins such as those from soy and other legumes have an adequate balance of essential amine acids to meet the protein needs of military personnel. These plant foods may have the advantage of decreasing the risk of cardiovascular disease due to their content of soluble carbohydrates, their lower sodium and lower fat contents, and the presence of other as yet unidentified substances.
Current intakes of protein among military populations are high and show no apparent harmful effects, provided fluid intake is adequate. There is little evidence of increased health risks from a high intake of dietary protein; however, an amine acid imbalance may be created with the use of single amine 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, although high-protein diets may indirectly stimulate renal stone formation and result in an increased renal workload because of 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 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.
Protein supplied in operational rations should be of high quality and digestibility. Energy intakes should be adequate, and sources of energy should be consumed within 2 hours of an intense bout of endurance exercise, to replace depleted muscle glycogen.
Soy food products are a healthful substitute for animal-based products; however individual products should be tested for their acceptability to soldiers.
Single amine 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 in-
fection 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).
IOM (Institute of Medicine). 1992. A Nutritional Assessment of U.S. Army Ranger Training Class 11/91. March 23. Washington, D.C.
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.