Insulin resistance in aged man: relationship between impaired glucose tolerance and decreased insulin activity on branched-chain amino acids.

The effects of glucose-induced hyperinsulinemia on plasma amino acid levels were measured in 50 subjects divided into five age groups. Following an oral glucose load the plasma levels of most amino acids decreased, the decline being more pronounced for the three branched-chain amino acids (valine, isoleucine, and leucine). A progressive insulin resistance was proved on the basis of an age-related impaired glucose tolerance and a normal or increased insulin response. The plasma disappearance of branched-chain amino acids significantly correlated with age (r = -.514). The effects of the prevailing plasma insulin on branched-chain amino acids, measured by the ratio of amino acid changes per total insulin response, progressively declined in older subjects (P = .0005), and strictly correlated with age (r = .652). Insulin resistance in the elderly similarly affects glucose and branched-chain amino acid metabolism, with possible relevant effects on whole-body protein turnover.