Effect of poor diabetic control and obesity on whole body protein metabolism in man

We have investigated whole body protein turnover in the fasted state in five normal men, five male Type 1 diabetic patients off insulin therapy, and five obese women, using IV ¹³C-leucine as a tracer. In diabetic patients, there was, as expected, a greater net loss of protein in the fasted state than in normal subjects. However, contrary to animal and studies in vitro, our diabetic patients in the fasted state showed a greater rate of protein synthesis than normal subjects (P< 0.01). The increased net loss of protein in diabetic patients compared with normal subjects arose because, in the diabetic patients, protein breakdown was increased even more than protein synthesis under the conditions of this study. Plasma leucine concentration was higher in diabetic and in insulin-insensitive obese patients than in normal subjects (p< 0.01), and higher in diabetic than in obese patients (p<0.05). The rate of protein synthesis per kg lean body mass was also higher in diabetic patients than in obese or normal subjects (P<0.01), and higher in obese than in normal subjects (p<0.05). We conclude that, in human subjects, whole body leucine and protein metabolism are very sensitive to the action of insulin.