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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.
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