The roles of estrogen and progesterone in regulating carbohydrate and fat utilization at rest and during exercise.

OBJECTIVE Compared with men, women use more fat and less carbohydrate to fuel exercise at the same relative intensity. Circulating levels of estrogen and progesterone are likely to play an important role in explaining this gender difference in exercise substrate utilization. METHODS Studies, mainly using animal models, have shown that estrogen increases fatty acid availability (lipolysis) and decreases carbohydrate availability and uptake. Studies conducted in humans corroborate the reduction in carbohydrate turnover and oxidation in the presence of estrogen, but the impact on fatty acid availability and utilization is less clear. RESULTS The effect of circulating estrogen may be mediated, at least in part, by changes in the sensitivity of stored carbohydrate and lipids to mobilization in response to epinephrine. The role of progesterone in metabolic regulation during exercise has not been systematically studied in humans. CONCLUSIONS Understanding the role of the ovarian hormones in fat and carbohydrate metabolism during exercise may have practical applications in terms of understanding the metabolic consequences of amenorrhea, menopause, and hormone replacement therapy (HRT).