The capacity to burn fat as fuel for exercise may have important implications for sporting performance, with dietary fat intake positively influencing this ability.

Endurance performance and the ability to burn fat will be measured in women runners following the consumption of 3 diets varying in the amount of fat and carbohydrate.

Dietary fat intake positively influences the ability to burn fat during exercise in women but not men, whereas carbohydrate intake negatively influences fat oxidation in both sexes. The independent nature of dietary fat intake as a predictor of the ability to burn fat in women suggests that in conditions of adequate carbohydrate intake providing additional fat may increase fat oxidation in women whereas it does not in men. It is of interest to explore if indeed women are responsive (i.e., increase in fat oxidation) to short-term increases in dietary fat intake induced by overfeeding (adequate carbohydrate) or if as appears to be the case in men reduced carbohydrate intake as typically employed in high-fat, low carbohydrate dietary studies is also a prerequisite for enhancing fat oxidation in women, and whether this translates into a difference in exercise endurance performance.

Inclusion Criteria:

• BMI >17.0 < 25 kg/m2
• Good General Health
• Accustomed to vigorous physical activity
• Run > 2 times per week
• V̇O2max >50ml/kg/min
• Weight Stable > last 6months
• Non Smoker
• Pre-menopausal, and either eumenorrheic and regularly menstruating, or using monophasic hormonal oral contraceptives for > 3 months.

Exclusion Criteria:

• Currently taking part in another scientific/clinical study
• Taking any prescription drug / supplement thought to influence metabolism
• Following unusual dietary practices (such as intermittent fasting or low carbohydrate diets)
• Pregnant
• Breast Feeding