Association of BMI, fitness, and mortality in patients with diabetes: Evaluating the obesity paradox in the Henry Ford exercise Testing Project (FIT project) cohort

OBJECTIVE: To determine the effect of fitness on the association between BMI and mortality among patients with diabetes.

RESEARCH DESIGN AND METHODS: We identified 8,528 patients with diabetes (self-report, medication use, or electronic medical record diagnosis) from the Henry Ford Exercise Testing Project (FIT Project). Patients with a BMI <18.5 kg/m 2 or cancer were excluded. Fitness was measured as the METs achieved during a physician-referred treadmill stress test and categorized as low (<6), moderate (6-9.9), or high (≥10). Adjusted hazard ratios for mortality were calculated using standard BMI (kilograms per meter squared) cutoffs of normal (18.5-24.9), overweight (25-29.9), and obese (≥30). Adjusted splines centered at 22.5 kg/m 2 were used to examine BMI as a continuous variable.

RESULTS: Patients had a mean age of 58 ± 11 years (49% women) with 1,319 deaths over a mean follow-up of 10.0 ± 4.1 years. Overall, obese patients had a 30% lower mortality hazard ( P < 0.001) compared with normal-weight patients. In adjusted spline modeling, higher BMI as a continuous variable was predominantly associated with a lower mortality risk in the lowest fitness group and among patients with moderate fitness and BMI ≥30 kg/m 2. Compared with the lowest fitness group, patients with higher fitness had an ∼50% (6-9.9 METs) and 70% (≥10 METs) lower mortality hazard regardless of BMI ( P < 0.001).

CONCLUSIONS: Among patients with diabetes, the obesity paradox was less pronounced for patients with the highest fitness level, and these patients also had the lowest risk of mortality.