As we've discussed, getting the right balance of carbohydrates, protein and healthy fats is key to staying energized during a long run.
Let's take a closer look at each category, starting with carbs.
Carbohydrates are the No. 1 source of energy for endurance athletes, primarily for the glycogen [source: Tufts].
For Andrews, the long-distance runner from Kansas City, simple foods like whole-wheat bagels and oatmeal are part of his running diet.
"I really like bagels," Andrews said. "They're very dense, a good carb-to-weight ratio, they're typically a whole grain, and they're convenient. I definitely eat a lot of bagels."
Stick to complex carbs, like high-fiber grains found in whole-grain breads, pastas and oatmeal, as well as fruits and vegetables [source: Tufts]. Like many other runners, bananas are a favorite of Andrews, because they're easy on the stomach and pack a lot of carbs.
As for protein, the key here is lean meat, like poultry or fish, and eggs. Meat takes longer to digest, so the less dense the better.
Many runners like Andrews also prefer nut butters, like peanut or almond, because they spread easy and pack a lot of protein.
If you're vegetarian or vegan, foods like nut butters or tofu are great protein sources. In fact, Andrews knows a number of ultra-marathoners who "have a [vegetarian/vegan] diet that you wouldn't have seen 20 to 30 years ago and to think, it can support high-mileage."
Regardless of dietary restrictions, make sure to include some sort of protein. It's necessary for rebuilding muscle during an intense run [source: Daniloff].
And let's don't forget that last category, fats.
Athletes want to steer clear of "unhealthy" fats, like the saturated fats found in butter and whole milk [source: Tufts]. Healthy fats, like those found in lean meats and low-fat dairy products, are needed by the human body. Yogurt and low-fat milk are good choices.
Some basic food staples, like nuts, eggs or yogurt, will provide a healthy dose of both protein and fat before a run. Just remember to give yourself a few hours between eating and going on a long run.
And a final note: No runner's diet is complete without plenty of hydration. Make sure to drink water before and during a long run to replace fluids lost through sweat.