Background/objectives: This study investigates age-dependent changes in resting metabolic rate (RMR) considering changes in body composition and fat distribution within the longitudinal study on nutrition and health status in an aging population in Giessen (GISELA), Germany, using three different approaches.
Subjects/methods: In approach 1 cross-sectional data from 358 female and 155 male participants of the GISELA study were evaluated (mean age of 67.4 +/- 5.9 and 66.9 +/- 5.2 y, respectively). In approach 2 longitudinal data of 107 female and 55 male subjects who participated over a follow up period of 10 years were analysed. In approach 3 all data obtained at a total of 3033 visits from 363 women and 153 men between 1994 and 2006 were evaluated. The mean duration of follow-up was eight years. RMR was assessed by indirect calorimetry.
Results: Approach 1: RMR correlates significantly negatively with age in women and men. Considering fat free mass, fat mass, and WHR, age proved to be a significant predictor of RMR in both sexes in multiple regression analysis; RMR falls by 11.2 kJ/d and 34.1 kJ/d per year in females and males, respectively. Approach 2: In males but not in females RMR decreases significantly in the course of the follow up. After ten years measured RMR is significantly lower than expected RMR predicted on the basis of body composition and fat distribution in females and males. Deviations correspond to a decline in RMR by 11.4 and 27.5 kJ/d per year independently of changes in body composition and fat distribution. Approach 3: Results of the mixed linear model show that RMR decreases in the course of aging in both women and men; after considering changes in body composition and fat distribution respective decreases were 8.7 and 30.7 kJ/d per year.
Conclusions: These results indicate that the decline in RMR with advancing age cannot be totally due to changes in body composition.