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Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise--a randomized controlled trial in overweight sedentary males.
The amount of weight loss induced by exercise is often disappointing. A diet-induced negative energy balance triggers compensatory mechanisms, e.g., lower metabolic rate and increased appetite. However, knowledge about potential compensatory mechanisms triggered by increased aerobic exercise is limited. A randomized controlled trial was performed in healthy, sedentary, moderately overweight young men to examine the effects of increasing doses of aerobic exercise on body composition, accumulated energy balance, and the degree of compensation. Eighteen participants were randomized to a continuous sedentary control group, 21 to a moderate-exercise (MOD; 300 kcal/day), and 22 to a high-exercise (HIGH; 600 kcal/day) group for 13 wk, corresponding to ∼30 and 60 min of daily aerobic exercise, respectively. Body weight (MOD: -3.6 kg, P < 0.001; HIGH: -2.7 kg, P = 0.01) and fat mass (MOD: -4.0 kg, P < 0.001 and HIGH: -3.8 kg, P < 0.001) decreased similarly in both exercise groups. Although the exercise-induced energy expenditure in HIGH was twice that of MOD, the resulting accumulated energy balance, calculated from changes in body composition, was not different (MOD: -39.6 Mcal, HIGH: -34.3 Mcal, not significant). Energy balance was 83% more negative than expected in MOD, while it was 20% less negative than expected in HIGH. No statistically significant changes were found in energy intake or nonexercise physical activity that could explain the different compensatory responses associated with 30 vs. 60 min of daily aerobic exercise. In conclusion, a similar body fat loss was obtained regardless of exercise dose. A moderate dose of exercise induced a markedly greater than expected negative energy balance, while a higher dose induced a small but quantifiable degree of compensation.
COMMENT: One more-less is more-result. In this study the investigators learned that an intensive exercise program (600 Kcal/day) actually yielded poorer results than a more moderate program (300 Kcal/day) in terms of weight loss. The intensive program appeared to increase food intake and reduce physical activity when the subjects were not exercising. In contrast, the 300 Kcal/day group were more active between exercise sessions and did not appear to change their eating patterns.