The aim of the present study was to investigate the relationship between resting metabolic rate (RMR) and fat-free mass, fat mass, and body fat distribution in 164 women (age 60 to 85 years; body mass index [BMI], 18.5 to 35.6 kg/m(2)) and 98 men (age 60 to 85 years; BMI, 18.3 to 36.5 kg/m(2)). After an overnight fast, RMR was assessed by indirect calorimetry and body composition by bioelectrical impedance analysis. Waist-to-hip ratio (WHR) was used to determine fat distribution. Results from linear regression analysis showed that most of the variance in RMR could be attributed to fat-free mass in women (R(2) = 0.54) and men (R(2) = 0.44), respectively. Fat mass explained an additional 3% and 2% of the variability in RMR in women and men, respectively. In stepwise multiple regression analysis, considering body composition and fat distribution, only fat-free mass and WHR were significant predictors of RMR in both sexes. In addition to fat-free mass, in women 6% and in men 8% of the variability in RMR was attributable to WHR. Grouping subjects according to their WHR, RMR, and RMR adjusted for fat-free mass and fat mass showed a significant increase with increasing WHR in both sexes. Results indicate that RMR not only depends on fat-free mass but also is influenced by fat mass, especially by fat distribution. These findings support our hypothesis of an elevated RMR with increasing abdominal body fat as a direct consequence of its greater metabolic activity.
Copyright 2001 by W.B. Saunders Company