Background

Previous studies have shown individual differences in compensatory responses to both acute and chronic exercise, often through increased energy intake. Fat mass (FM) and fat-free mass (FFM) help regulate energy intake through various pathways, integrated in the brain to influence behavior. The purpose of this study was to examine how changes in body composition contribute to compensatory appetite changes across 24 weeks of aerobic exercise training.

Methods

Participants (n=104, 73% F, 49±11 years) completed 24 weeks of supervised exercise in the E-MECHANIC Trial. Expected weight loss (EWL) was calculated based on the individual exercise prescription using a dynamic energy balance model. Body composition by DXA, objective energy intake by test meals, retrospective appetite by visual analog scales (VAS), and the Eating Inventory (Hunger, Restraint, Disinhibition) were collected before and after exercise training. Change scores were used as predictors of the percent of EWL achieved (%EWL).

Results

The mean %EWL for the sample was 45% (± 106%), demonstrating substantial heterogeneity in the response to exercise training. Changes in FM and FFM were both independent predictors of %EWL (p < 0.001), but only FFM remained significant once controlling for absolute weight change (partial correlation: r = -0.27, p = 0.006). Objective energy intake was not associated with FM, FFM, or %EWL. Change in FFM was positively associated with change in prospective food consumption (r = 0.24, p = 0.01), while change in FM was positively associated with change in Disinhibition (r = 0.21, p = 0.04).

Conclusions

Participants who gained FFM throughout exercise training achieved a lower %EWL, regardless of FM and absolute weight changes. Those who gained FFM showed greater increases in prospective food consumption, while those who gained FM became more disinhibited in regards to food. These results highlight two separate appetitive mechanisms whereby changes in body composition may attenuate EWL in response to exercise.