Mj. Toth et al., RATES OF FREE FATTY-ACID APPEARANCE AND FAT OXIDATION IN HEALTHY YOUNGER AND OLDER MEN, Journal of applied physiology, 80(2), 1996, pp. 506-511
Alterations in the mobilization and oxidation of fat may partially acc
ount for age-related alterations in body composition. To investigate a
ge-related alterations in fat metabolism, we compared basal rate of ap
pearance of free fatty acids (FFA(app)) and total body fat oxidation a
s measured by infusions of [C-14]palmitate and indirect calorimetry, r
espectively, in 18 younger (23 +/- 1 yr) and 30 older (69 +/- 1 yr) me
n. We also examined whether age-related differences in body compositio
n, body fat distribution, peak oxygen consumption, dietary intake, and
/or fasting insulin levels may explain age-related variation in FFA(ap
p) and total body fat oxidation. The FFA(app) showed a tendency to be
higher in older compared with younger men (1,134 +/- 184 vs. 680 +/- 1
05 mu mol/min; P = 0.07), whereas total body fat oxidation was similar
between groups (257 +/- 25 vs. 222 +/- 9 mu mol/min). The estimated r
ate of nonoxidative disposal of free fatty acids showed a tendency to
be higher in the older (913 +/- 182 mu mol/min) than in younger men (4
23 +/- 103 mu mol/min; P = 0.06). Fat-free mass was the most significa
nt predictor of FFA(app) in younger (r = 0.63; P < 0.01) and older (r
= 0.41; P < 0.05) men. These results suggest that older men recruit fa
tty acids from adipose tissue stores in excess of the energy needs of
respiring tissue. However, variation in FFA(app) between the age group
s could not be explained by differences in body habitus or fasting ins
ulin levels.