Sex differences in exercise, metabolism and nutritional implications

Abstract

For years, most researchers and clinicians have considered that men and women respond similarly to endurance exercise. It is now quite apparent that women oxidize more lipid and less carbohydrate and amino acids as compared to men during low and moderate intensity endurance exercise. Studies using estrogen supplementation in animals and humans have demonstrated higher fat oxidation with lower carbohydrate and amino acid oxidation. Women appear to be genetically “primed” for higher lipid oxidation with greater transcript abundance for a number of genes encoding proteins involved in lipid transport and beta-oxidation. We have recently found higher protein content for key components of beta-oxidation and lipid metabolism. In general, women are metabolically primed for higher lipid oxidation during exercise with carbohydrate and amino acid metabolic changes responding to the higher lipid oxidation. We and others, have demonstrated that women have an attenuated ability to glycogen load which is partially a function of a relatively lower energy intake and an inability to reach the 8–8.5 g carbohydrate/kg body mass that is required for carbohydrate loading. Even with extra energy and carbohydrate women still have a slightly attenuated ability to carbohydrate load in response to the “modified Sherman protocol”. In contrast, women show similar glycogen re-synthesis rates in response to carbohydrate and protein supplement post-exercise and can oxidize exogenous carbohydrate during exercise at least as well as men. Given the lesser amino acid oxidation during exercise, it is not surprising that protein requirements would be subsequently less negatively impacted by endurance exercise in women verses men. For very well trained male athletes the protein requirement can be as high as 1.7 g/kg/day and in women the highest that we have yet seen is 1.3–1.4 g/kg/day. It is important to note that protein requirements are not increased for recreationally active men or women.