ABSTRACT
Muscle loss can be expected whenever the rate of muscle protein breakdown and utilization for energy exceeds the rate of protein synthesis. Methods have been developed that allow the measurement of the rates of protein synthesis, degradation, and oxidation simultaneously using amino acid tracers.1,2,* Improved understanding of factors that in uence protein turnover is essential for developing nutritional therapies for the prevention of muscle loss. The turnover of body proteins and skeletal muscle protein (SMP) is discussed in this chapter. The biological signi cance of protein turnover is described in Section 4.1. Baseline values for whole body protein turnover are presented in Section 4.2. The contribution of different organs to whole body protein turnover is discussed in Section 4.3. Current research suggests that illness affects protein turnover (Section 4.4). Finally, the effect of bioactive peptides and related supplements on the whole body and SMP turnover is described in Section 4.5. Illness produces marked increases in the extent of protein synthesis, breakdown, and oxidation. More research is needed to ascertain whether particular interventions can increase protein synthesis or decrease muscle protein breakdown and oxidation, or both.
