The effect of exercise training on glucose tolerance and insulin sensitivity was studied in rats receiving a modern-westernized high fat diet, in which 42% of total energy was provided in fat. Rats were neither permitted to exercise actively (gorup E) or forced to be in the sedentary condition (group S) for the first two weeks. In the next 2 weeks, rats in both groups were subjected to either active exercise (group EE and SE) or the sedentary condition (group ES and SS). An intraperitoneal glucose tolerance test and insulin sensitivity test were performed at the end of the first and the second 2 weeks.
No significant difference was found among the groups in blood glucose levels after glucose challenge. However, the insulin levels in the group E, SE and EE were significantly lower than those in the groups S, SS and ES, respectively. Sensitivity to exogenous isulin was higher in the group EE and SE than in the group ES and SS, respectively. The epididymal fat pads of the groups S, ES, and SS were heavier than those of the group E, EE and SE, respectively. These findings altogether showed that exercise training restrained the incerase in the body fat of rats receiving a high fat diet and improved their sensitivity to endogenous and exogenous insulin. However, discontinuation of exercise rapidly lowered the insulin sensitivity. These findings suggest that continuous exercise is especially important for the prevention and treatment of diabetes mellitus, even under a westernized high fat diet.