Effect Of Exercise-induced Weight Loss On 24 Hour Energy Metabolism

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Exercise usually results in less weight loss than expected. It is therefore postulated that changes in energy expenditure (EE) and/or compensatory increases in energy intake (EI) occur to counteract energy deficits induced by exercise. PURPOSE: Compare changes in all components of daily energy expenditure (24hrEE) after 24 weeks of exercise training between varying doses of exercise recommended for weight loss. METHODS: Forty-one (28 F, 13 M) obese (35.2±3.7 kg/m2) middle aged (47.8±12.5 y), sedentary individuals from the Examination of Mechanisms of Exercise-induced Weight Compensation (E-MECHANIC) study were randomized to either a healthy living control group (HL, n=13) or a supervised, controlled aerobic exercise intervention that achieved 8 kcal/kg of body weight/week (KKW, n=14) or 20 KKW (n=14). 24hEE (metabolic chamber), total daily energy expenditure (TDEE, by doubly labeled water), energy intake (by Intake-Balance method), and VO2peak (by graded exercise test) were measured before and after the intervention. RESULTS: Compared to the HL group, VO2peak increased in the 8 KKW (p=.004) and 20 KKW (p<.0001) groups. With 20 KKW, TDEE (and 24hrEE) increased (p=.04) and weight loss (-2.5±0.9 kg, p=.04) was significant but approximately half of what was expected based on the increase in energy expenditure from exercise. Fat mass (-2.1±0.8 kg, p=.02) but not fat-free mass (-0.4±0.3 kg, p=.79) was also significantly reduced. A 151 kcal/d energy deficit was detected at week 24. The increase in TDEE is attributed to the increased physical activity (p=.03) and not to changes in EE during sleep, arousal or the thermic effect of food. Besides physical activity, the largest change in EE was a reduction in spontaneous physical activity by ~15% (p=.04). With 8 KKW, there was no significant weight or body composition change and no significant increase in TDEE. An energy deficit of 23 kcal/d was detected at week 24. None of the components of EE were changed in the 8 KKW group. CONCLUSIONS: Structured aerobic exercise that expends up to 1800 kcal/wk increased TDEE but produces less weight loss than expected possibly due to compensatory increases in EI and behavioral adaptations that could lead to reduced spontaneous physical activity.