OBJECTIVE To investigate the associations between changes in body composition and fitness after exercise training and changes in hemoglobin A_1c (HbA_1c) in individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS Participants (n = 201) were randomized to aerobic, resistance, or combined training for 9 months. HbA_1c, waist circumference, total and trunk fat mass, appendicular fat mass, lean body mass, isokinetic leg muscle strength, peak O₂ uptake, and estimated METs were assessed at baseline and follow-up. Change in HbA_1c was evaluated across quartiles of change in body composition and fitness.

RESULTS Change in HbA_1c was associated with changes in body weight (r = 0.13, P = 0.052), waist circumference (r = 0.17, P = 0.013), trunk fat mass (r = 0.19, P = 0.005), and estimated METs (r = −0.16, P = 0.023). There was a trend in change in HbA_1c across quartiles of waist circumference (P = 0.011), trunk fat mass (P = 0.020), and estimated METs (P = 0.011). Participants with increased estimated METs and reduced trunk fat mass had greater odds of having reduced HbA_1c after training (3.48, 1.46–8.31). Finally, participants with increased estimated METs and reduced waist circumference were 2.81 (1.13–6.98) times more likely to have reduced HbA_1c and type 2 diabetes medication use than those who without improved fitness and central adiposity.

CONCLUSIONS In patients with type 2 diabetes, a reduction in central adiposity and increase in fitness were the most prominent predictors of the change in HbA_1c in response to exercise training.