Determining how your body prefers to burn fuel is valuable information for endurance athletes. Why? When you’re competing in events longer than 3-4 hours, getting your carbohydrate (CHO) intake right is key. If you don’t take in enough, you risk running low or depleting your CHO stores—which means you might also be risking a DNF (did not finish). But if you take in too much, your gut will shut down; leaving you feeling bloated and nauseated. Neither scenario plays out well in the end.