Dose-Dependent Effects of Exercise and Diet on Insulin Sensitivity and Secretion

Purpose A single bout of aerobic exercise increases insulin sensitivity the next day. The effects of exercise on insulin secretion, the role of exercise-induced energy deficit, and possible dose-response relationships are not well understood. This study aimed to evaluate insulin sensitivity and insulin secretion after progressively greater negative energy balance induced by exercise or diet. Methods Acute energy deficits (20% or 40% of weight maintenance needs) were induced by a single day of aerobic exercise (cycling at moderate intensity, n = 13) or dietary restriction (n = 19) in healthy men and women (age, 26 +/- 2 yr; body mass index, 21.8 +/- 0.5 kg center dot m(-2)). Intravenous glucose tolerance tests in conjunction with minimal modeling were performed the next morning, and blood samples were collected for 3 h to measure glucose and insulin concentrations. Results Insulin sensitivity increased linearly after exercise-induced energy deficits (P = 0.007) but did not change after equivalent diet-induced energy deficits (P = 0.673). Acute insulin response decreased after both exercise (P < 0.001) and dietary restriction (P = 0.005). The disposition index and glucose effectiveness were not affected by exercise (P = 0.138 and 0.808, respectively), but both decreased after 40% dietary restriction (P = 0.048 and 0.002, respectively). Conclusions These results indicate that insulin sensitivity and insulin secretion are related to exercise energy expenditure, albeit in a different fashion (insulin sensitivity increases linearly, whereas insulin secretion drops to a nadir with a low exercise dose and does not decrease further). These changes cannot be replicated by equivalent energy deficits induced by dietary restriction, suggesting that exercise and diet have different effects on the mechanisms regulating glucose homeostasis.