Exercise training elevates RMR during moderate but not severe dietary restriction in obese male rats

This study examined the effects of 11 wk of exercise training (E) on resting O2 uptake (RMR) and the composition of diet-induced weight loss in obese male Sprague-Dawley rats (n = 48). The rats underwent one of three levels of dietary treatment: ad libitum (AL), moderate restriction (MR), and severe restriction (SR). Compared with AL-CC (cage confined; 647 +/- 13 g), the AL-E (84% of AL-CC), MR-CC (77%), MR-E (77%), SR-CC (63%), and SR-E (63%) groups were all reduced in body mass. At the MR level, E significantly reduced fat mass (FM; MR-CC 73 +/- 5, MR-E 45 +/- 5 g) and increased water mass (WM; MR-CC 307 +/- 5, MR-E 329 +/- 5 g) compared with CC. In contrast, no significant differences existed between the SR-CC and SR-E groups. Exercise training did not result in conservation of protein mass at any level of dietary intake. Exercise training significantly elevated RMR (on a kg0.75 basis) by approximately 7% for the AL-E and MR-E groups compared with their respective dietary counterparts. These findings may help reconcile the conflicting results present in the literature with respect to the effects of exercise training during diet-induced weight loss. That is, studies using relatively severe dietary restrictions are less likely to demonstrate exercise-induced changes in RMR, FM, and WM than those employing moderate dietary restrictions.