A low-carb diet may be the trendy way to lose weight, but it’s not the way to train for a race. (Read: running is better than dieting!) When preparing for a marathon, a majority of your daily calories should come from carbohydrates — about 55 to 60 percent — in order to fully fuel your workouts. Bring it on, right? Healthy sources of carbs include whole grains (whole wheat pasta, brown rice, and quinoa), fruits (berries, melons, and apples), and vegetables (sweet potatoes, carrots, and leafy greens).