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Your dietary needs depend on such factors as your experience level, health issues and how your body responds to different foods, according to Dina Griffin, a board-certified sports dietitian and registered dietitian nutritionist at The Nutrition Mechanic. "I like to look at quality nutrition choices and ensure runners are getting enough to support their training and keep energy availability up," she says.
That said, there are a few basic principles of nutritious eating to fuel your marathon training and offer you the best chance of success on race day. Start with these guidelines, and then consider yourself an experiment of one. Jot down quick notes about what you eat and how your body, mind and gastrointestinal system feel afterward, suggests Tom Holland, a certified sports nutritionist and author of Swim, Bike, Run, Eat.
With that method, you can hone in on the optimal marathon diet — for you. The best pre-marathon diet may even change for you over time, Holland says; at age 50, he's still constantly adjusting his own fueling equation.
Mind Your Macronutrients
All foods are made up of three basic components called macronutrients — carbohydrates, protein and fats. They're all important for distance runners, says registered dietitian nutritionist Lydia Nader, founder of RUN Performance Nutrition in Chicago.
Carbohydrates serve as the primary energy source for endurance athletes. For most marathoners, Nader recommends aiming for about 5 grams of carbs per kilogram of body weight — that's 2.2 pounds — per day (so, a 150-pound runner would need about 340 grams).
Protein helps repair muscle damage and wards off fatigue late in the race. Griffin says she often starts planning athletes' diets by ensuring their protein needs are met — she aims for 1.4 to 2 grams per kilogram per day (95 to 136 grams for a 150-pound runner).
Finally, fats also provide energy, keep hormone levels balanced and fight inflammation, which builds up when you train hard. Omega-3 fatty acids — found in fatty fish, walnuts and flaxseeds — play an especially critical role, Nader says. She advises athletes to consume foods high in these fats at least two to three times weekly.
While it's true that some athletes see success on a high-fat, low-carb diet, that doesn't work for many people, Nader says. Fats aren't as easy to burn quickly, like carbs are. In order to train your body to use them efficiently, you have to be diligent about restricting your carb intake.
For many runners, adding this extra stress on top of training is counterproductive, she says. "Carbohydrates allow for a little bit more flexibility, a little more leeway," Nader explains. Plus, a low-carb approach may impair performance in many endurance athletes, according to a December 2016 study in the Journal of Physiology.
Consider Quality, Too
Your eating habits aren't all a numbers game. The quality of the foods you eat matters, too. Aim for whole, minimally processed picks like lean meats and fish, whole grains, dairy and a wide variety of fruits and vegetables. They offer the most micronutrients, the vitamins and minerals your body needs to support your training and recovery, and keep your immune system healthy.
Most of your carbs should be what are called complex carbohydrates — foods rich in fiber and nutrients like whole grains, most vegetables and beans, Nader says. But simple carbohydrates like fruit, starchy vegetables and sugars have their place, too; they provide fast energy that can give you a much-needed jolt before or during a race.
Fuel on — and After — the Run
Your muscles' stores of glycogen — the type of sugar they use for energy — are substantially depleted after about 90 minutes of moderate to high-intensity exercise, notes a September 2016 study in American Journal of Physiology: Endocrinology and Metabolism.
You'll need to take in more glycogen during long training runs and your marathon. Sports nutrition guidelines recommend aiming for 30 to 90 grams per hour; start on the low end if you're smaller or prone to stomach distress, Griffin says.
Begin practicing mid-run fueling once your training sessions reach that 90-minute mark. That way, you'll have plenty of time to practice and see what works for you and your gut, Griffin says. You can use pre-packaged gels, chews and sports drinks — or even tote your own whole foods, such as bananas or dates.
It's also important to refuel your energy stores after a hard workout or a race. Having a snack or a meal with a three-to-one ratio of carbs to protein within an hour or so after a long run or race jumpstarts your recovery process, replenishing your glycogen and helping repair damage to your muscles, Nader says.
Drink Up — and Add Electrolytes
Hydration is another key aspect of fueling yourself properly for a marathon, Nader points out. Dehydrated muscles don't work as well and are also more prone to soreness and slower recovery later. She recommends a baseline of at least two liters per day of water, though you might need more depending on your weight, your mileage and the time of year. Drink enough fluids that your urine is the color of lemonade, not too dark but not too light.
Keep in mind it is possible to drink too much water. This can contribute to a dangerous condition called hyponatremia, in which your body's concentrations of sodium are diluted. Replenishing your stores of electrolytes — minerals that include sodium, potassium and magnesium — also matters to proper fluid balance. You can get them through foods, including bananas and salt, or use a drink mix or sports nutrition protein that includes them, Nader says.
Power Up for Your Race
You've trained hard and eaten well for weeks — and with your last few pre-race meals, you have a chance to put the finishing touches on your preparations. Just like you practice eating on the run, use your long training runs as opportunities to test out what you'll eat the night before and the morning of your race. Experiment with both the ingredients of your meals and the timing to figure out what works best for you, Griffin says.
Pasta dinners and bagel breakfasts are many runners' go-tos for a reason — simple carbs provide fast energy and tend to be easier on the gut. Griffin recommends including some protein at dinner — perhaps one-quarter to one-third of the plate — to provide what she calls "sticking power." Including protein in your morning meal, such as nut butter or eggs, slows digestion a bit so the release of energy lasts until the gun goes off at the starting line.
You can start with that template, adjust to see what works, then make sure you have access to all those ingredients the night before and on the day of your race, especially if you're traveling. With your meals locked down, you can concentrate on staying calm and running your best.
- Journal of Physiology: "Low Carbohydrate, High Fat Diet Impairs Exercise Economy and Negates the Performance Benefit From Intensified Training in Elite Race Walkers"
- American Journal of Physiology: Endocrinology and Metabolism: "Liver Glycogen Metabolism During and After Prolonged Endurance-Type Exercise"
- Fitness: The Top 7 Runner Foods
- Wall Street Journal: Why Runners Can't Eat Whatever They Want