This chapter is concerned with proteins, the fundamental structures of life. They exist as functional elements within every cell and undergo extensive metabolic interaction. This widespread metabolic interaction is intimately linked to the metabolism of energy and other nutrients. At the most basic level, proteins are made from a combination of 20 different amino acids, which determines the structure and function. Dietary protein and exercise are the two key stimuli that promote positive protein turnover, which can be accurately and reliably measured using stable isotope methods. The potency of the anabolic response to dietary protein is dependent upon the protein quality, which can be measured via the Digestible Indispensable Amino Acid Score, Protein Digestibility Corrected Amino Acid Score, and/or using stable isotope tracers. In situations of protein deficiency, significant body mass can be lost, drastically impairing health and quality of life, requiring dietary protein therapy to help overcome/manage these conditions.
