Muscle mass depletion

Protein is a long-term reserve of glucose and energy. Protein is also an important structural component of cells. Prolonged protein use for energy and glucose supplies depletes muscle mass. 

As the model suggests, the dietary need for amino acids is determined by the rates of depletion of the free amino acid pool by oxidation or synthesis of protein. During steady state conditions, the contribution to the free pool from dietary intake and protein breakdown should be exactly balanced by the flux out of the pool to synthesis and oxidation. Any condition that increases deposition of protein in the body or the rate of amino acid oxidation should produce an increased need for protein. For example, muscle hypertrophy is dependent on a positive balance of the protein turnover process. If synthesis of protein exceeds the catabolism of protein, then muscle mass will increase and the free amino acid pool would be depleted. Thus, a net increase in protein requires an increase in intake or a decrease in oxidation. Likewise, the same arguments hold for an increase in oxidation of amino acids. 

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