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which supports Young's belief that the indispensable amino acid requirement is higher than currently recommended. Thus, the controversy over requirements for IAAs is still unresolved.

The implications of this debate for the current state of knowledge of protein and amino acid requirements for the military depend in part on the current intake of dietary protein and amino acids by military personnel and in part on other factors influencing protein requirements in these individuals, as discussed below.

STRESSORS THAT INFLUENCE PROTEIN REQUIREMENTS

As discussed by Friedl in Chapter 3, the stressors encountered most frequently by military personnel are high levels of physical activity with Or without energy restriction; illness, injury, and infection; and environmental extremes. Although each of these stressors may somehow influence protein metabolism and protein requirements directly, they also produce changes in hormonal status that can influence protein metabolism as well. The impact of each of these factors on protein metabolism and requirements has been the subject of intense investigation in the civilian research community. A brief summary of relevant findings is presented here.

Physical Activity and Energy Restriction

The question of whether individuals who routinely engage in intensely physical occupational or athletic activities have increased requirements for dietary protein appears to have arisen from the observations that during exercise, muscle protein is utilized for fuel and that exercise can lead to an increase in muscle mass. However, whether protein requirements are in fact increased by physical activity is unclear and a subject of intense controversy. In Chapter 11, Rennie reviews the role of protein and its breakdown products, amino acids, in exercising muscle and discusses changes in protein metabolism induced by energy deficit.

Exercise and Amino Acid Catabolism

A major function of amino acid breakdown in muscle during periods of exercise is to supply tricarboxylic acid intermediates (anaplerosis) so that the oxidation of acetyl coenzyme A (CoA) can proceed at rates appropriate to the energy needs of the contractile apparatus. The exercise-induced increase in muscle alanine production may be a marker for this process. Specifically, glutamate can react with pyruvate, via the action of alanine-aminotransferase, to produce alanine and α-ketoglutarate. The latter then feeds into the TCA cycle,



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