Synergistic improvement of glucose tolerance by sucrose feeding and exercise training

The interactive effects of exercise training (5-7 wk) and sucrose consumption (ad libitum feeding of a 32% sucrose solution and Purina chow) on intravenous glucose tolerance and plasma insulin levels were investigated using a 2 X 2 experimental design. Rats were divided in Purina-sedentary, Purina-trained, sucrose-sedentary, and sucrose-trained groups. Sucrose feeding of sedentary animals significantly increased basal and glucose-stimulated insulin levels and improved basal glycemia and glucose tolerance. On the other hand, exercise training of Purina-fed animals significantly reduced basal as well as glucose-stimulated insulinemia without altering basal glycemia or glucose tolerance. Such a sparing effect of exercise training on insulin requirements was not as evident in rats consuming sucrose. These animals displayed a reduced basal glycemia (P less than 0.01) with normal basal insulin levels. Their glucose tolerance was markedly improved (P less than 0.01) but their insulin response during intravenous glucose tolerance test remained as high as in sucrose-sedentary animals. Results from these studies indicate that sucrose feeding of sedentary animals leads to hyperinsulinemia without compensatory insulin resistance, resulting in an improvement of glucose tolerance, exercise training increases the sensitivity of peripheral tissues to insulin, and the marked improvement of glucose tolerance observed in sucrose-trained animals results from a synergistic combination of the above two factors, i.e., increased insulinemia (induced by diet) and enhanced insulin sensitivity (induced by training).