Exercise intensity does not affect depression of resting metabolic rate during severe diet restriction in male...

This study examined the effects of high and low intensity exercise on the resting metabolic rate during severe dietary restriction. We hypothesized that exercise would attenuate and/or offset the decline in resting metabolic rate during energy-deficit conditions. Thirty-two male 90-d-old Sprague-Dawley rats were divided into four groups: control, diet restriction only, diet restriction plus high intensity exercise, and diet restriction plus low intensity exercise. The body weights of the diet-restricted groups were rapidly reduced over 5 wk until rats in these three groups weighted 64% of control weight, and this difference in body weight was maintained for the last 5 wk of the study. The high and low intensity exercise groups ran 5 d/wk at 75 and 37.5%, respectively, of maximal running speed for 45 and 90 min/d, respectively. Resting metabolic rate (23-h oxygen uptake) was measured during wk 2, 4, 6, 8 and 10. Resting metabolic rate for the three diet-restricted groups was significantly lower (25-37%) than for the controls for all measurements. Exercise training had no effect on the diet-induced depression of resting metabolic rate, with the diet-restricted groups differing among each other by < 2% during the measurement periods. During severe diet-restriction, exercise-induced elevations of resting metabolic rate seem to be greatly reduced or eliminated. This absence of an exercise effect on resting metabolic rate persisted through 5 wk of reduced body weight maintenance. We conclude that during severe diet restriction, exercise offers no "protective" or enhancing effect on resting metabolic rate.