This study compared the benefits of a high-fat diet (HF – 60% calories from fat) or a high-carbohydrate diet (HC – 60% calories from carbohydrate) in two groups of sled dogs that underwent aerobic rounds of exercise. Key parameters such as blood free fatty acids (FFA), triglycerides (TG), vitamin E, glucose and lipase activity were measured before and after each test to assess the effect of the diet. HF diet caused increased FFA and TG concentration before and after exercise but no changes in the other parameters compared to HC diet, suggesting an enhanced availability of lipid stores during exercise. However, more studies are needed to know if this means a better performance.