Effects of aerobic or resistance exercise and/or diet on glucose toleranceand plasma insulin levels in obese men

OBJECTIVE - This study had two objectives. First, we examined whether the i nfluence of diet combined with either aerobic (DA) (n = 10) or resistance ( DR) (n = 10) exercise has effects on insulin and glucose levels that are di fferent in obese men. Second, we tried to determine whether the combination of diet and exercise is associated with improvements in insulin and glucos e levels that are greater than those associated with diet alone (DO) (n = 9 ). RESEARCH DESIGN AND METHODS - Insulin and glucose levels were measured afte r an overnight fast and a 75-g oral glucose challenge (OGTT). Visceral adip ose tissue (AT), subcutaneous AT, and skeletal muscle were measured by magn etic resonance imaging (MRI) before and after treatment (16 weeks). RESULTS - Reductions in weight (12.4 +/- 3.8 kg) and in visceral (37 +/- 15 .1%) and subcutaneous AT (24.3 +/- 8.6%) were nor different between treatme nts (P > 0.05). Skeletal muscle was maintained in the DA and DR groups but was reduced (7.3 +/- 2.8%) in the DO group (P < 0.05). independent of treat ment, fasting glucose and OGTT glucose did not change (P > 0.05). However, fasting insulin, OGTT insulin, and the insulin-to-glucose ratio decreased w ithin all treatments (P < 0.05). Reductions in the OGTT insulin area under the curve were greater (P < 0.05) within the DA (52 +/- 12%) and DR (42 +/- 17%) treatments than in the DO (20 +/- 15%) treatment. Collapsed across gr oup, reductions in visceral AT were related to reductions in fasting and OG TT glucose (P < 0.05), whereas reductions in abdominal subcutaneous AT corr elated with reductions in fasting insulin (P < 0.05). CONCLUSIONS - Weight loss induced by diet and aerobic or resistance exercis e has similar positive effects on lowering fasting and OGTT insulin values that are greater than those with diet alone. Because changes in glucose and insulin were related to reductions in visceral and abdominal subcutaneous AT,we conclude that reduction in abdominal obesity consequent to diet and e xercise-induced weight loss is important for attaining improvements in plas ma insulin levels, observations that strengthen the concept that abdominal obesity has an important role in mediating insulin resistance.