Effects of exercise and weight loss on leucine turnover in different types of obesity.

These studies were performed to determine whether protein turnover during exercise and after weight loss is influenced by obesity and body fat distribution. Leucine carbon flux was measured before, during, and after 2.5 h of bicycle exercise in 10 upper body obese, 9 lower body obese, and 6 nonobese, age-matched, premenopausal women. The obese women then followed an energy-restricted diet for 16 wk, resulting in approximately 8 kg weight loss. Baseline leucine carbon flux was greater (P < 0.01) in obese women than in nonobese women but decreased in a similar fashion in response to exercise in all groups. There were no differences between upper body and lower body obese women during exercise. After weight loss, baseline leucine carbon flux decreased (P < 0.05) similarly in both groups of obese women and was further suppressed by exercise. Thus obesity phenotype has no specific effect on either baseline protein turnover or the antiproteolytic response to moderate intensity exercise or weight loss. We conclude that the previously observed defect in insulin suppression of leucine flux in upper body obese women appears related to insulin resistance and does not represent an inherent abnormality of protein metabolism.