The Effect of sex steroid hormones on substrate oxidation during prolonged submaximal exercise in women.

In animals, female sex steroid hormones (SS, estrogens-progesterone) influence the energy substrate that is metabolized. Human research on this issue is controversial. This study examined whether changes in circulating SS hormone levels affected the carbohydrate-lipid metabolism during submaximal prolonged (60 min) exercise. Young, physically active females were studied. Four were classified as anovulatory-oligomenorrheic and four were classified as ovulatory-eumenorrheic. Subject responses were pooled to form one group (n = 8) and then their responses under low (L) and high (H) pharmaceutically manipulated SS hormone conditions were examined. During exercise, the mean oxygen consumption levels were 1.70 +/- 0.10/ x min(-1) for L-SS and 1.75 +/- 0.11/ x min(-1) for H-SS (p = 0.07), respectively. The respiratory exchange ratio (RER) responses were significantly different during exercise between the conditions: 0.93 +/- 0.04 for L-SS and 0.90 +/- 0.04 for H-SS (p < 0.05), respectively. RER responses were utilized to calculate substrate oxidation. Significantly less carbohydrate oxidation was found in the H-SS condition as compared to the L-SS condition (p < 0.05). Lipid oxidation was also significantly different, but for this measure, the levels of oxidation were greater in the H-SS than in the L-SS condition (p < 0.05). Finally, total energy expenditure for the 60 min of exercise was not significantly different between the hormonal conditions. Results suggest that sex steroid hormones have an impact upon substrate oxidation in women during exercise. Specifically, high circulating concentrations of the SS hormones result in an enhanced reliance upon the oxidation of lipid as an energy substrate and consequently induce a reduction in carbohydrate oxidation. The mechanism inducing this "metabolism shift" appears due to sex steroid hormones directly and indirectly increasing lipid mobilization and lipolysis.