Submitted on December 26, 2006
Accepted on July 18, 2007
Changes in 24 h Substrate Oxidation in Older and Younger Men in Response to Exercise
Edward L. Melanson1*, William T. Donahoo2, Gary K. Grunwald3, and Robert S. Schwartz4
1 Center for Human Nutrition and Division of Endocrinology, Metabolism, and Diabetes, University of Colorado Health Sciences Center, Denver, Colorado, United States
2 Kaiser Permanente of Colorado, Denver, Colorado, United States
3 Center for Human Nutrition, University of Colorado Health Sciences Center, Denver, Colorado, United States
4 Division of Geriatric Medicine, University of Colorado Health Sciences Center, Denver, Colorado, United States
* To whom correspondence should be addressed. E-mail: ed.melanson{at}uchsc.edu.
The purpose of this study was to compare 24 h substrate oxidation in older (OM, 60-75 yrs, N=7) and younger (YM, 20-30 yrs, N=7) men. Subjects were studied on sedentary day (CON) and on a day with exercise (EX, net energy expenditure = 300 kcal). Plasma glucose and free fatty acids were also measured at several time points during the 24 h measurement. Weight was not different in OM and YM (mean ± SD, 84.8 ± 16.9 vs. 81.4 ± 10.4 kg, respectively), although percent body fat was slightly higher in OM (25.9 ± 3.5% vs. 21.9 ± 9.7%, P=0.17). 24 h energy expenditure did not differ in OM and YM on the CON (mean ± SE, 2449 ± 162 vs. 2484 ± 104 kcal/D, respectively) or EX (2902 ± 154 vs. 2978 ± 122 kcal/D) days. Under both conditions, 24 h RQ was significantly lower and fat oxidation significantly higher in OM. Glucose concentrations were not different at any time point, but plasma FFA concentrations were higher in OM, particularly following meals. Thus, under these controlled conditions, 24 hr fat oxidation was not reduced and was in fact greater in OM. We speculate that differences in the availability of circulating FFA in the postprandial state contributed to the observed differences in 24 h fat oxidation in OM and YM.
