She recommends that runners load up on carbs from whole grains, fruits, vegetables, legumes and dairy. Fall short on carbs and your body will start burning other sources of fuel—namely, protein, which your body needs for other functions.
"Protein is essential in building up muscle that's been broken down over the long miles of training," says Nisevich Bede, who also writes RunnersWorld.com's nutrition blog, Fuel School. Most runners need between .6 and .9 grams of protein per pound of body weight, and runners in the midst of tough marathon training should aim toward the high end of that estimate. The best sources include seafood, skinless poultry, legumes, low-fat beef and pork, eggs and low-fat dairy, says Nisevich Bede.
Long-distance runners especially need to fuel up before a run. "Aim for a meal high in carbs, low in fiber and fat, and moderate to low in protein," says Nisevich Bede, "and give yourself at least an hour—hopefully two or three—to digest before hitting the road."
PLUS: The Right Way to Carbo-Load
You Want to Lose Weight
Many runners assume that logging 10, 20, 30 or more miles per week will automatically lead to drastic weight loss. But the truth is, while running is an excellent calorie burner (burning on average 100 calories per mile), you won't lose weight if you don't also take your diet into consideration. That's because all that exercise makes you hungry—and it's easy to overdo it and consume all of the calories you just burned (or more) during that five-mile run.
So how do you successfully pair running and weight loss? The key is to keep up your running routine while slightly reducing your daily calorie intake—by no more than 250 to 500 calories per day, says Nisevich Bede. "Cut any more, and fatigue and injury can set in."
Many runners find it hard to cut back on calories at all, given their increased hunger from training, which is why your diet should be loaded with two specific nutrients that help combat a growling stomach: "Fiber and protein fill you up and keep you feeling fuller longer," says Nisevich Bede.
More: How Many Calories Do You Need?
Vegetables, fruits, beans and whole grains are some of the best sources of fiber, while protein from lean meats, fish, low-fat dairy and eggs can help keep hunger at bay. In fact, studies show that eating a high-protein breakfast instead of a high-carb one can help reduce the total number of calories you eat throughout the rest of the day.
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Another surprising key to losing weight is keeping snacks in your diet—not cutting them out, as many runners mistakenly do. "By consuming a few small snacks throughout the day, runners keep blood-sugar levels more stable and avoid spikes and drops that can cause fatigue and extreme hunger to set in," says Nisevich Bede.
The most weight-loss-friendly snacks are between 150 and 250 calories and are high in fiber or protein (again, both of which are filling), such as apple slices with a bit of nut butter, whole-grain toast with a slice of low-fat cheese or yogurt topped with high-protein granola.
The only time you don't want a high-fiber, high-protein snack is immediately before a run. "Foods high in fiber can send you sprinting for the bathroom, while protein and especially fat take longer to digest and can slow you down," says Nisevich Bede. But you still need a prerun snack, since without it, you may not have enough energy on board to run hard, limiting the number of calories you could burn.