Basal fat oxidation decreases with aging in women

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 non-smoking 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.