Background

Exercise induced weight loss is often less than expected. Compensatory mechanisms serve to resist body fat loss and may be equivocal to exercise energy expenditure (ExEE). These mechanisms may be behavioral (eating more, less non-exercise physical activity, alterations in hunger hormones) or metabolic (resting metabolic rate, respiratory quotient). The extent to which exercise frequency, duration, intensity and ExEE has on influencing compensation is controversial. Determining how these variables impact energy compensation would help health care providers prescribe exercise with greater probability of creating a negative energy balance and subsequent weight loss.

Methods

30 participants (20 female) aged 18 to 40 years performed aerobic exercise 2 or 6 days/week for 12 weeks. Resting metabolism, body composition (DXA), sub-maximal VO2 were assessed. Exercise sessions were evaluated for time, duration, intensity, and ExEE (indirect calorimetry). Energy compensation was determined by comparing changes in bodily energy stores (DXA) to total ExEE and expressed as both % energy compensated (compensation index, CI) and total energy compensated (kcal).

Results

Exercise intensity, ExEE, exercise frequency (days per week) and exercise duration did not predict CI (p>0.3) or total energy compensated (p>0.1). Exercise duration and ExEE predicted % fat loss (p<0.05) when controlling for total energy compensated. Greater fat mass was lost (-1.77 kg) when weekly ExEE exceeded 2,000 kcal compared to under 2,000 kcal (-0.41 kg, p<0.05), with no differences in CI or total energy compensated (p>0.48) between ExEE groups.

Conclusions

Greater exercise intensity, frequency, ExEE or exercise duration do not promote greater CI or total energy compensated. When energy compensated is held constant, greater ExEE and duration promote fat loss. ExEE over 2,000 kcal/week is needed to overcome CI and reduce fat mass.