Lower resting metabolic rate in the elderly may not be entirely due to changes in body composition

Abstract

Objective: To investigate whether or not the lower resting metabolic rate (RMR) in the elderly is entirely due to changes in body composition. Design: Cross-sectional data of 132 female (age 69.975.5 y, body mass index (BMI) 26.574.0 kg/m 2 ) and 84 male (age 68.975.1 y, BMI 26.172.8 kg/m 2 ) participants of the longitudinal study on nutrition and health status in an aging population of Giessen, Germany, as well as that of 159 young women (age 24.873.0 y, BMI 21.172.5 kg/m 2 ) and 67 young men (age 26.873.4 y, BMI 23.372.4 kg/m 2 ) were analysed. RMR was measured by indirect calorimetry after an overnight fast and body composition was estimated by bioelectrical impedance analysis and predictive equations from the literature. Analysis of covariance was used to adjust RMR for body composition, body fat distribution and smoking habits. Additionally, RMR that is to be expected theoretically, was calculated on the basis of the subjects' body composition and the specific metabolic rate of the different organs and was compared to measured RMR. Results: Compared to young subjects adjusted RMR was significantly lower in elderly women (5432782 vs 5809770 kJ/day, Po0.01) and men (6971799 vs 75587121 kJ/day, Po0.001). In both elderly women and men, measured RMR was markedly lower than calculated RMR (À6257404, À5157570 kJ/day). By contrast, measured and calculated RMR were nearly the same in young men (1597612 kJ/day); in young women the difference between measured and calculated RMR was only À3007457 kJ/day. In both sexes, these differences are significantly larger in the elderly when compared to young adults. Conclusion: These results support the point of view that the decline in RMR with advancing age cannot be totally due to changes in body composition.

Longitudinal changes in energy expenditure in an elderly German population: a 12-year follow-up

“…This question has been addressed in several cross-sectional studies with inconsistent results. Although some authors could not find significant differences in RMR of young and elderly subjects after adjustment for body composition (Welle et al, 1996;Bosy-Westphal et al, 2003), other studies showed that RMR in elderly subjects was significantly lower in comparison with young adults even after correcting for body composition (Klausen et al, 1997;Gallagher et al, 2000;Hunter et al, 2001;Krems et al, 2005). Results of our investigations show that the decline in RMR is not entirely due to changes in body composition.…”

Basal metabolic rate and thyroid hormones of late-middle-aged and older human subjects: the ZENITH study

“…When BMR was adjusted for FFM by ANCOVA, it was still lower in Italian volunteers than in middle-aged French subjects (À12%). These results confirm those obtained by other authors (Fukagawa et al, 1990;Visser et al, 1995;Klausen et al, 1997;Das et al, 2001;Krems et al, 2005). It has been postulated that the relationship of BMR to FFM in older individuals can be confounded by a change in the composition of FFM (Bosy-Westphal et al, 2003) and may be mediated by other factors such as sympathetic nervous system activity, thyroid hormone status, uncoupling activity, etc.…”

Age–Related Differences in Body Composition in Egyptian Obese Females

“…The present results agree also with other studies reported that fat mass was increased with age, but contradicts findings reported that there is little or no further gain in fat mass in older age 40-55 [17][18][19][20]. Generally, BMR depends on body composition as expressed by fat-free mass (FFM) and fat mass (FM) and on gender, age, physical activity, and nutritional status [26][27][28]. The lower BMR of older adults may be due in part to slowed organ metabolic rates and this may contribute to changes in FM and FFM.…”