Resting metabolic rate and diet-induced thermogenesis in young and elderly subjects: relationship with body composition, fat distribution, and physical activity level

To investigate the relationship between age and energy expenditure, resting metabolic rate (RMR) and diet-induced thermogenesis (DII; for 180 mm after a 1.3-MJ meal) were measured by indirect calorimetry in 56 young and 103 elderly subjects. In addition, the influence of body corn- position, body-fat distribution, and physical activity level on this relationship was studied. RMR was significantly lower in elderly (3.98 ± 0.46 and 3.33 ± 0.39 kJ/min for men and women, respectively) than in young (5.29 ± 0.53 and 4.08 ± 0.33 kJ/min for men and women, respectively) subjects, which persisted after adjustment for body composition. DII was significantly lower in older than in younger men (126 ± 27 vs 154 ± 34 kJ/180 mm) but not in women (111 ± 26 vs 115 ± 25 kJ/180 mm). The difference in men disappeared after ad- justment for body composition. No clear relation between physical activity level and RMR or DII was observed. These results demonstrate a relationship of age per se with RMR but not with DII. Am J Clin Nutr 1995;61:772-8.