Effects of fat mass and body fat distribution on resting metabolic rate inthe elderly

The aim of the present study was to investigate the relationship between re sting metabolic rate (RMR) and fat-free mass, fat mass, and body fat distri bution 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)). Afte r an overnight fast RMR was assessed by indirect calorimetry and body compo sition by bioelectrical impedance analysis, Waist-to-hip ratio (WHR) was us ed to determine fat distribution. Results from linear regression analysis s howed 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 explain ed an additional 3% and 2% of the variability in RMR in women and men, resp ectively. In stepwise multiple regression analysis, considering body compos ition and fat distribution, only fat-free mass and WHR were significant pre dictors 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 subj ects according to their WHR, RMR, and RMR adjusted for fat-free mass and fa t mass showed a significant increase with increasing WHR in both sexes. Res ults indicate that RMR not only depends on fat-free mass but also is influe nced by fat mass, especially by fat distribution. These findings support ou r hypothesis of an elevated RMR with increasing abdominal body fat as a dir ect consequence of its greater metabolic activity. Copyright (C) 2001 by W. B. Saunders Company.