Structured aerobic exercise may produce less weight loss than expected

1. In this study, significant weight loss occurred in the group performing aerobic exercise that expended 20 kcal/kg/week but was only half of what was expected if there was no compensation.

2. In the group that expended 8 kcal/kg/week, there was no change in weight and no significant change in any component of energy expenditure.

Evidence Rating Level: 1 (Excellent)

Energy expenditure is known to increase in proportion to the amount of physical activity. However, the contribution to total energy expenditure is likely offset by decreases in other components of daily energy expenditure. Since the extent to which the energy deficit induced by exercise is not well understood, the present study was designed to identify mechanisms responsible for weight compensation. The primary objective of this study was to evaluate changes in components of daily energy expenditure after 24 weeks of exercise training by comparing two doses of aerobic exercise.

This ancillary study of the Examination of Mechanisms of Exercise-induced Weight compensation study included 53 patients (n=13 controls, n=14 at 8 kcal/kg/week of aerobic exercise, n=15 at 20 kca/kg/week of aerobic exercise) with a body mass index between 25 kg/m² and 45 kg/m² who were healthy and not currently exercising >20 minutes 3 times per week. Notable exclusion criteria included prior participation in a weight loss program and prior bariatric surgery. Todal daily energy expenditure (TDEE) was measured in free-living condition by doubly labeled water and in sedentary conditions in a metabolic chamber over 24hrs.

Results demonstrated that the 20 kcal/kg/week group had significant weight loss, although only half of what was expected, likely due to decreased overall 24-hour energy expenditure. In addition, the 8 kcal/kg/week group did not experience any weight loss and had no significant change in overall energy expenditure. This study was limited by the environment of the metabolic chamber which may not apply to free living conditions. However, the results of this study were strengthened due to its success at ensuring individuals adhered to their respective exercise regimen.

Click to read the study in Medicine & Science in Sports & Exercise

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