OBJECTIVE: To test the hypothesis that the increase in fat mass observed wi
th aging might be related to a decrease in whole-body fat oxidation.
SUBJECTS AND MEASUREMENTS: Forty volunteers had measurements of sleeping an
d 24 h substrate oxidation in calorimetric chambers, body composition with
the O-18 dilution technique, VO2max, and fiber composition analysis from a
biopsy of vastus lateralis. They were divided into 10 young women, 10 young
men, 10 elderly women and 10 elderly men.
RESULTS: Sleeping fat oxidation and 24 h fat oxidation were lower in women
than in men and in elderly than in young participants. Sleeping fat oxidati
on was correlated to fat-free mass and energy balance (multivariate analysi
s). Twenty four hour fat oxidation was correlated to total energy expenditu
re and energy balance (multivariate analysis). After adjustment for differe
nces in these factors, sleeping and 24 h fat oxidation were no longer diffe
rent between age and sex groups. None of the parameters of macronutrient me
tabolism was correlated with muscle fiber composition.
CONCLUSION: Our data suggest that fat oxidation is lower in elderly subject
s. This difference could favour fat mass gain if fat intake is not adequate
ly reduced. Differences in fat-free mass and in total energy expenditure ap
pear to participate in the reduction in fat oxidation.