Perspectives in Diabetes A Reduced-Fat Diet and Aerobic Exercise in Japanese Americans With Impaired Glucose Tolerance Decreases Intra-Abdominal Fat and Improves Insulin Sensitivity but not -Cell Function

Lifestyle modification reduces the risk of developing type 2 diabetes and may have its effect through improving insulin sensitivity, -cell function, or both. To determine whether diet and exercise improve insulin sensitivity and/or -cell function and to evaluate these effects over time, we quantified insulin sensitivity and the acute insulin response to glucose (AIRg) in 62 Japanese Americans (age 56.5 1.3 years; mean SE) with impaired glucose tolerance (IGT) who were randomized to the American Heart Association (AHA) Step 2 diet plus endurance exercise (n 30) versus the AHA Step 1 diet plus stretching (n 32) for 24 months. -Cell function (disposition index [DI]) was calculated as Si AIRg, where Si is the insulin sensitivity index. The incremental area under the curve for glucose (incAUCg) was calculated from a 75-g oral glucose tolerance test. Intra-abdominal fat (IAF) and subcutaneous fat (SCF) areas were measured by computed tomography. At 24 months, the Step 2/endurance group had lower weight (63.1 2.4 vs. 71.3 2.9 kg; P 0.004) and IAF (75.0 7.9 vs. 112.7 10.4 cm; P 0.03) and SCF (196.5 18.0 vs. 227.7 19.9 cm; P < 0.001) areas, greater Si (4.7 0.5 vs. 3.3 0.3 10 5 min pmol 1 l ; P 0.01), and a trend toward lower AIRg (294.9 50.0 vs. 305.4 30.0 pmol/l; P 0.06) and incAUCg (8,217.3 350.7 vs. 8,902.0 367.2 mg dl 1 2 h ; P 0.08) compared with the Step 1/stretching group after adjusting for baseline values. There was no difference in the DI (P 0.7) between the groups. Si was associated with changes in weight (r 0.426, P 0.001) and IAF (r 0.395, P 0.003) and SCF (r 0.341, P 0.01) areas. Thus, the lifestyle modifications decreased weight and central adiposity and improved insulin sensitivity in Japanese Americans with IGT. However, such changes did not improve -cell function, suggesting that this degree of lifestyle modifications may be limited in preventing type 2 diabetes over the long term. Diabetes 54:340–347, 2005