OBJECTIVE: This study evaluated whether a commercial weight-loss product (Lean System 7) would result in less reduction in resting metabolic rate (RMR) in overweight subjects on a calorie-restricted diet and exercise regimen than in subjects using diet and exercise alone. METHODS: In this randomized, double-blind, placebo-controlled study, healthy overweight adults were given three capsules of a commercial weight-loss product twice daily or an identical placebo and followed a calorie-restricted diet and an exercise program for 8 wk. RMR, body weight, body mass index, waist and hip circumferences, and body composition by dual-energy x-ray absorptiometry were measured at baseline and week 8. An intention-to-treat analysis was performed. RESULTS: Of 47 adults enrolled, 35 completed the study. Subjects taking the commercial weight-loss product had a significant (P = 0.03) increase in RMR, 7.2% increase versus 0.7% decrease in the placebo group. Subjects taking the commercial weight-loss product also had a significant (P = 0.04) decrease in hip circumference, 3.78 cm versus 2.07 cm in the placebo group. There were no other statistically significant differences in any other outcome variable, diet composition, exercise compliance, or adverse events. CONCLUSION: The results of this study showed that administration of a commercial weight-loss product to overweight adults in conjunction with a calorie-restricted diet and moderate exercise program effectively reverses the decrease in RMR associated with calorie restriction within this study population. The commercial weight-loss product was well tolerated, and there were no serious adverse events over the 8 wk studied.