Sexual dimorphism in the effects of exercise on metabolism of lipids to support resting metabolism

Abstract

Exercise training is generally a healthful activity and an effective intervention for reducing the risk of numerous chronic diseases including cardiovascular disease and diabetes. This is likely both a result of prevention of weight gain over time and direct effects of exercise on metabolism of lipids and the other macronutrient classes. Importantly, a single bout of exercise can alter lipid metabolism and metabolic rate for hours and even into the day following exercise, so individuals who regularly exercise, even if not performed every single day, overall could experience a substantial change in their resting metabolism that would reduce risk for metabolic diseases. However, resting metabolism does not respond similarly in all individuals to exercise participation, and indeed gender or sex is a major determinant of the response of resting lipid metabolism to prior exercise. In order to fully appreciate the metabolic effects and health benefits of exercise, the differences between men and women must be considered. In this article, the differences in the effects of exercise on resting metabolic rate, fuel selection after exercise, as well as the shuttling of triglyceride and fatty acids between tissues are discussed. Furthermore, concepts related to sex differences in the precision of homeostatic control and sex differences in the integration of metabolism between various organs are considered.

Keywords: EPOC; RMR; fat oxidation; physical activity; post-exercise recovery.

Figure 1

Summary of the effects of an acute endurance exercise bout on subsequent metabolism of lipids in the support of the resting metabolic rate is shown. M > F, response of males greater than that of females to a recent exercise bout. M = F, responses similar between males and females to a recent exercise bout. ?, Results for investigations of sex differences not yet reported. 1, recent exercise increases subsequent RMR (total substrate oxidation) in men but not significantly in women. 2, Exercise increases subsequent post-absorptive whole-body lipolysis in men but not in women. This higher lipolysis in men increases availability of FFA, which causes greater accentuation of post-absorptive fat oxidation in men than women. 3, Food intake generally inhibits subsequent fat oxidation, such that postprandial lipid oxidation is lower than post-absorptive lipid oxidation, but prior exercise blunts this inhibition of fat oxidation; thus, postprandial fat oxidation is enhanced by a recent exercise bout (similarly in men and women). 4, Food intake leads to transient elevation of plasma TG concentration (postprandial lipemia), but recent exercise blunts postprandial lipemia, likely to a greater extent in men than women. 5, Prior exercise blunts hepatic VLDL-TG secretion, but the sex difference is not yet clearly defined in the literature.