Reduced plasma concentration of branched-chain amino acids in sarcopenic older subjects: a cross-sectional study.

Branched-chain amino acids (BCAA) are essential amino acids that are necessary for muscle mass maintenance. Little is known about the plasma concentrations of BCAA and the protein intake in relation to sarcopenia. We aimed to compare the non-fasting plasma concentrations of the BCAA and the dietary protein intake between sarcopenic and non-sarcopenic older adults. Norwegian older home-dwelling adults (≥70 years) were invited to a cross-sectional study with no other exclusion criteria than age. Sarcopenic subjects were defined by the diagnostic criteria by the European Working Group on Sarcopenia in Older People. Non-fasting plasma concentrations of eight amino acids were quantified using NMR spectroscopy. Protein intake was assessed using 2×24-h dietary recalls. In this study, ninety out of 417 subjects (22 %) were sarcopenic, and more women (32 %) than men (11 %) were sarcopenic (P<0·0001). Sex-adjusted non-fasting plasma concentrations of leucine and isoleucine, and the absolute intake of protein (g/d), were significantly lower among the sarcopenic subjects, when compared with non-sarcopenic subjects (P=0·003, P=0·026 and P=0·003, respectively). A similar protein intake was observed in the two groups when adjusted for body weight (BW) and sex (1·1 g protein/kg BW per d; P=0·50). We show that sarcopenia is associated with reduced non-fasting plasma concentration of the BCAA leucine and isoleucine, and lower absolute intake of protein. More studies are needed to clarify the clinical relevance of these findings, related to maintenance of muscle mass and prevention of sarcopenia.