Rationale: Two RCTs testing the effects of weight loss on changes in glucose tolerance and insulin also had measures of abdominal fat, as measured by waist circumference (369, 373). In each study, waist circumference was reduced along with weight loss and glucose tolerance improved. Neither study was designed to test whether reductions in waist circumference improved glucose tolerance or diabetic control independent of weight loss.
Evidence exists from observational studies that abdominal fat is related to impaired glucose tolerance or type 2 diabetes independent of BMI. For instance, a few studies have found a significant relationship between abdominal fat loss and improvement in glucose tolerance and insulin action (415-418).