Carbo-Loaded: Sexual Dimorphism in Carbohydrate and Lipid Metabolism in Male and Female Endurance Athletes

Until recently, sports nutrition dietary recommendations have primarily been driven by the nutritional needs of male athletes. However, it has become apparent that substrate utilization is subject to differences in sex-specific metabolic regulation. New information about the role of sex in metabolism has been particularly important for creating guidelines for female athletes. Current dietary recommendations emphasize increasing carbohydrate intake before training through a process commonly known as “carbo-loading.” The objective of this study is to examine how female endurance athletes metabolize carbohydrates and fats differently than male endurance athletes. Previous studies have shown that endurance training increases the body’s ability to utilize fat as the primary fuel source. There is evidence that this increased reliance on fats over carbohydrates is higher in females than in males due to the presence of both estrogen and progesterone. Taking sex hormones into consideration, specifically estrogen and progesterone, this study will look at the relationship between carbohydrate and lipid metabolism throughout the female athlete’s menstrual cycle. Differences in metabolism will be measured by total fat oxidation and respiratory exchange ratios (RER) across three different diet types (control, high-carbohydrate, and high-fat, low-carbohydrate), the menstrual cycle, and between sexes. This study aims to show that because there exists an increased preference for fats during endurance exercise, female endurance athletes may benefit from diets higher in fat than carbohydrates prior to training and competition