Ensure you're fueling your body with enough daily calories using this calculation: Start with 13 calories per pound of body weight for your baseline needs and add 300 calories for every additional 60 minutes of training. This calculation is not an exact science, but it will give you a good ballpark estimate.
Choose High Quality Carbs
High–quality carbohydrates provide you with continuous energy for long runs. For increased endurance eat an assortment of winning picks every day of the week, including vegetables, fruit, beans, lentils, quinoa, barley, bulgur, farro, millet, brown and wild rice, whole–grain pasta, high–fiber cereal, and whole–wheat bread.
Pack in Protein
Protein helps to maintain and build muscle mass, including that in the quads and hamstrings — a runner's greatest asset. Best bets include fish and shellfish, lentils, starchy beans (such as black, kidney, and chickpeas), egg whites, skinless chicken and turkey, pork tenderloin, lean beef, soy foods (such as tofu, tempeh, and edamame), and nonfat/low–fat dairy (yogurt, milk, and cheese).
Mix It Up at Meals
Make meals a combo of high-quality carbohydrates, protein, and healthy fats. For breakfast try vanilla Greek yogurt with sliced bananas and toasted nuts or an egg–white omelet stuffed with veggies and cheese with whole–wheat toast; for lunch enjoy a grilled–chicken wrap with lettuce and tomato rolled in a whole–grain tortilla or lentil–bean chili with a whole–grain roll; for dinner prepare shrimp–and–broccoli stir–fry over brown rice or grilled salmon with sautéed spinach and a baked sweet potato.
Enjoy a carbohydrate–rich snack that offers up some protein within an hour before starting a training run. Try a banana and a serving of string cheese, apple slices topped with nut butter, whole–grain cereal with skim milk, a bowl of hearty vegetable soup, or a nutrition bar.
Minimize Soreness With Anti-Inflammatory Foods
These foods possess properties that help reduce inflammation and soreness: salmon, sardines, walnuts, and ground flaxseed (all great sources of omega 3's); broccoli, Brussels sprouts, bell pepper, and citrus fruits (which all contain vitamin C); sweet potato, carrots, pumpkin, spinach, and kale (all sources of carotenoids); berries, cherries, and purple/red grapes (rich in anthocyanins); apples, onions, tomatoes, deep colored lettuce, and apricots (sources of quercetin) and grated ginger, which you can try adding to stir-fries, curries, soups, and sautéed vegetables.
Hydrate, Hydrate, Hydrate
Keep your muscles happy and hydrated by drinking plenty of water throughout the day. Before long runs stick with water. During long runs alternate between water and sports drinks. Continue to hydrate after you've finished your run and assess fluid status through urine color. Ideally, your urine should be pale yellow (like diluted lemonade), not cloudy or dark (like apple juice).
Load Up on Carbs the Day Before
Eat plenty of high–quality carbohydrate the day before your big run to ensure you'll have ample stored energy, called muscle glycogen. Think whole grains, fruit, and vegetables!
Your Pre-Marathon Power Breakfast
Stick with familiar foods and eat a breakfast rich in high–quality carbs with some protein. Winning morning meals include a whole–wheat bagel topped with nut butter and banana slices, scrambled eggs with chopped tomato and whole–wheat toast, oatmeal topped with berries and nuts/seeds, or yogurt with granola and fruit.
Stay Energized During the Marathon
Nibble on carbs every 60 to 90 minutes to keep your blood–sugar level steady and your energy up. Try sports drinks and gels/chews, as well as dried and fresh fruit.
Replenish Your Body After Long Runs
For optimal recovery: Within the first few hours of finishing a long run or marathon, consume about 50% of your body weight in carb grams — plus 10 to 20 grams of protein. Eat half within the first 30 minutes of finishing your run and the rest at any point within the next two hours. For example, if you weigh 160 pounds, you'll want to consume 80 grams of carbs and 10 to 20 grams of protein. For optimal recovery, eat half within 30 minutes of finishing the race (e.g., a sports drink plus either a nutrition bar, soy crisps, or trail mix) — and the other half during the next two hours (e.g., turkey sandwich, or pizza with veggie toppings, a bowl of lentil soup, whole–grain pasta with tomato sauce and parmesan cheese, or a fruit/yogurt smoothie.