Varying Levels of Carbohydrate and Fat Diets for Ultramarathon Running: A Review on Performance and Health Outcomes

This literature review analyzed 20 studies (n=147) investigating the effects of a high-fat diet on ultrarunning performance and metabolism. Results suggest that a high-fat diet can improve fat oxidation during exercise and may improve ultrarunning performance in some cases, although the effects on performance and metabolic markers appear to be highly variable. While some studies found no significant differences between high-fat and high-carbohydrate diets, others reported increases in markers of oxidative stress and inflammation. Additionally, several studies found that a very low-carbohydrate, high-fat diet could decrease muscle glycogen levels, which could potentially have negative effects on performance. Overall, these findings suggest that a high-fat diet may have some benefits for ultrarunners, but the optimal macronutrient ratio for maximizing performance remains unclear. Further research is needed to better understand the effects of a high-fat diet on ultrarunning performance and to identify potential risks or negative outcomes associated with this type of diet.