Basal fat oxidation decreases with aging in women

Abstract

The present study tested the hypothesis that a decrease in basal fat oxidation in aging women is related to a loss of fat-free mass. Thirty-two nonsmoking women with a wide range of age (18–73 yr) were characterized for body composition (underwater weight), maximal aerobic capacity, and basal fat oxidation (indirect calorimetry). Results showed that fat oxidation was negatively correlated with age (r2 = 0.17, P = 0.017) but was positively correlated with the fat-free mass (r2 = 0.48, P < 0.0001) and with the level of aerobic fitness (maximal aerobic capacity) (r2 = 0.22, P = 0.007). Unexpectedly, fat oxidation had no relationship with fat mass (r2 = 0.07, P = 0.136). Partial correlation analysis showed that the decline in fat-free mass, and not the age or maximal O2 consumption, was the best single predictor of the decline in basal fat oxidation. These results support the theory that a decrease in fat oxidation with advancing age in healthy women is associated with a decrease in the fat-free mass and not age per se. Interventions that increase or preserve the quantity of fat-free mass (e.g., exercise training) may enhance fat oxidation and thus lessen the age-associated adiposity in women.