Associations among circulating branched-chain amino acids and tyrosine with muscle volume and glucose metabolism in individuals without diabetes

• Branched-chain amino acids (BCAA) positively associated with insulin sensitivity in individuals without diabetes.
• Muscle volume was important for circulating levels of BCAA and tyrosine (Tyr).
• BCAA correlated with increased fasting blood glucose and fasting immunoreactive insulin (IRI) levels.
• Serum BCAA and Tyr levels were higher in men than in women.
• Tyr did not affect insulin sensitivity but was associated with fasting IRI levels.

ObjectivesAmino acid metabolites, including branched-chain amino acids (BCAA) and tyrosine (Tyr), affect glucose metabolism. The effects of BCAA on insulin resistance in patients with diabetes seem to conflict with mechanisms determined in animal models and cultured cells. The aim of this study was to clarify the controversy surrounding the effects of BCAA by investigating the physiological effects of BCAA and Tyr on glucose metabolism in healthy community dwellers.MethodsWe investigated associations among BCAA and Tyr and metabolic parameters in 78 residents (median age, 52 y) of Mie, Japan, who did not have prediabetes, diabetes, or a body mass index >30 kg/m2.ResultsMuscle volume, serum BCAA, and Tyr levels were higher in men than in women (n = 32 and 46, respectively; all P < 0.0001). Stepwise multiple regression analysis associated BCAA positively with muscle volume (regression coefficient/t/p/95% confidence interval, 281.8/3.7/0.0004/129.7–433.8), fasting blood glucose (FBG; 12699.4/3.22/0.0020/4830.9–20567.8), fasting immunoreactive insulin (IRI; 8505.1/2.75/0.0078/2322.5–14687.6), and homeostasis model assessment of β-cell function (HOMA-β; 893.6/2.58/0.0122/201.8–1585.5), and negatively with the HOMA-insulin resistance (HOMA-IR; −9294.1/−2.89/0.0052/−15711.0 to −2877.1). Tyr positively correlated with fasting IRI (26/2.77/0.0072/7.3–44.7).ConclusionsInsulin sensitivity and muscle volume are positively associated with BCAA in individuals without diabetes. In turn, BCAA correlate with increased FBG and fasting IRI levels. Tyr correlated with fasting IRI, but not with insulin sensitivity.