Nutritional Biomarkers of Sarcopenia

Sarcopenia increases the risk of a number of deleterious health conditions and represents a major financial cost to our healthcare system. Among older adults who are hospitalized, those with sarcopenia on admission are 5-fold more likely to incur higher hospital costs than those without. The operational definition of sarcopenia is defined as meeting the criteria for all of the following: low muscle strength, low muscle quantity or quality, and low physical performance. The diagnosis of sarcopenia requires techniques that are both expensive and operator-dependent. Simple measurements, such as BMI, do not necessarily identify sarcopenia. Importantly, current techniques can only identify sarcopenia after a physical/functional impairment has occurred. Skeletal muscle amino acid kinetics predict muscle health and functionality. Altered amino acid kinetics lead to decrements in muscle mass, quality, and performance. Muscle response to circulating essential amino acids (EAA) determines muscle amino acid kinetics. Thus, this study proposes to characterize skeletal muscle amino acid kinetics to an EAA challenge, i.e., an oral amino acid tolerance test (OATT), in order to determine the state of muscle health. Analogous to the oral glucose tolerance test (OGTT) used to characterize alterations in glucose metabolism, the proposed OATT represents a potential low-cost solution to classifying patients' skeletal muscle health. The extrapolation of this work is the development of a simple analytical tool that would provide clinicians the ability to discern alterations in muscle amino acid kinetics prior to a loss of function.