While resting metabolic rate (RMR) is known to decline during periods of energy restriction, the effect of exercise training during weight loss on RMR is less clear. We studied separately the effect of energy restriction and exercise training on weight loss and RMR in a one-year randomized, controlled trial. One hundred twenty-one overweight, sedentary men (age 30-59) who were randomly assigned to a control (C), energy restriction only (D), or exercise only (E) group were examined at baseline and after one year for changes in RMR as measured by standard indirect calorimetry. Relative to controls, E increased fitness and jogged an average of 9.97 +/- 5.6 miles/week and did not change energy intake while D significantly reduced energy consumption. Both groups achieved significant weight loss and fat mass loss when compared to the controls at the end of one year. After one year, the D group showed a small yet significant decline in RMR (kcal/h and kcal/FFM/h) when compared to controls and exercisers, while the E group showed no significant changes. Therefore, in moderately overweight men, a one-year program of weight loss by energy restriction produced a significant decline in RMR while weight loss by exercise did not change RMR.