Pre-run snacks boost blood glucose levels, and can top off muscle carbohydrate stores — essential fuel for longer, harder runs. The more time for digestion, the larger the snack. For a snack two hours ahead, go for something rich in carbohydrates such as a bowl of cereal, peanut butter sandwich or small smoothie. This can help power your run and prevent hunger. Typically, 50 to 75 grams of easily-digested carbohydrates can be consumed two hours before a run without causing any stomach upset. . . . When short on time, go for lighter snacks that your body can digest quickly. Consider a handful of dry cereal or a slice of toast with jam. Aim for 15 to 25 grams of carbohydrates in the hour before a run. You also can pop in a carbohydrate gel or half an energy bar for easy digestion if you don’t have access to easy snack foods.