When adults initiate an exercise prescription, approximately 51% do so with a declared goal of weight loss. Decreasing adiposity correlates with disease risk reduction and, in some sport contexts, improved performance. However, exercise adherence is typically poor; within 6 months of engagement, expected attrition exceeds 50%. Those who fail to sustain the practice commonly report being discouraged by a lack of progress. Thus, it is important to identify and understand the variables that influence the rate of fat loss at the onset of an exercise program.

PURPOSE: To evaluate predictors of body composition improvement among diverse exercising populations.

METHODS: We enrolled subjects from two distinct populations: older diabetic patients with no history of exercise (n=67) and college-aged rugby athletes (n=12). Each population underwent baseline testing to assess body fat percent (BF%) prior to and following a period of exercise. The diabetic population performed structured, supervised exercise for 10 weeks; the athletic population performed unsupervised, unstructured exercise for 4 weeks. Multiple linear regression analyses, holding other explanatory variables constant, tested predictors of BF% change.

RESULTS: At baseline, the diabetic patients were 68.3 ± 10.7 years of age, had a body mass index (BMI) of 32.3 ± 6.7 kg/m2, and 39.3 ± 6.9% body fat. The rugby athletes were 19.6 ± 2.0 years of age, had a BMI of 25.2 ± 2.8 kg/m2, and 13.4 ± 4.3% body fat. Among diabetic patients, controlling for potential confounders, each additional point of baseline BF% predicted a 0.18-point reduction in BF% at post-test (p=0.010; 95% CI: -0.32 to -0.05); the overall model was significant (R2=0.395; p=0.002). Among rugby athletes, controlling for potential confounders, each additional point of baseline BF% predicted a 0.33-point reduction in post-test BF% (p=0.042; 95% CI: -0.65 to -0.02).

CONCLUSION: Among exercising diabetic and athletic populations, higher baseline BF% corresponded to greater improvements in body composition throughout the exercise intervention. Among athletic populations, this may mean more rapid improvements in sport performance; for diabetic populations, this may lead to greater improvements in glycemic control.