Effects of brief perturbations in energy balance on indices of glucose homeostasis in healthy lean men

Background: Little is known about the effects of short-term caloric restriction (CR) and overfeeding (OF) on glucose homeostasis in healthy lean individuals. In addition, it remains unclear whether the effects of CR and OF are reversed by a complementary feeding period.METHODS: Ten healthy men participated in two cycles of controlled 7-day periods of CR and refeeding (RF; protocol A), and OF and CR (protocol B) at 60% energy requirement. At baseline, insulin sensitivity (IS) was assessed by euglycemic clamp (M). Before and during each feeding cycle, fasting and oral glucose tolerance test-derived indices were used to estimate glucose tolerance, IS and glucose-stimulated insulin secretion.RESULTS: Clamp tests revealed normal IS at baseline (M-values 9.42.1 mg kg 1 min 1, coefficient of variation (CV) inter 22%). M-values were significantly correlated with indices of IS. In protocol A, CR-induced weight loss (3.00.4 kg) was associated with an increase in fasting IS. Postprandial IS and glucose-stimulated insulin secretion remained unchanged, but glucose tolerance decreased. RF decreased fasting and postprandial IS at increased glucose-stimulated insulin secretion. In protocol B, OF significantly increased the body weight (1.60.9 kg). Concomitantly, fasting and postprandial IS decreased at increased glucose-stimulated insulin secretion. Subsequent CR reversed these effects. Inter-individual variability in indices of glucose metabolism was high with coefficients of variation ranging from 9 to 59%.CONCLUSION: Significant changes in glucose metabolism are evident within 7-day periods of controlled OF and underfeeding. Although IS was impaired at the end of the CR-RF cycle, IS was normalized after the OF-CR cycle. At different feeding regimens, homeostatic responses of glucose metabolism were highly variable.