Race experts provide healthy eating tips and the best diet for successful marathon training to stay fueled on all your runs.

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When I decided to run the New York City Marathon with Team USA Endurance, a fundraising platform formed by the U.S. Olympic Committee to support fundraising efforts for the U.S. Olympic and Paralympic athletes at the upcoming games, my first concern was the training. But when I opened the U.S. Olympic Committee packet for the first time and began reading about how to complete a successful marathon, one line stood out to me: "The number one reason for dropping out of a marathon is gastrointestinal problems, not injury." Woah. 

"By practicing hydration and nutrition strategies during the long training runs, one finds out what each individual runner's stomach can tolerate, but it also trains the gut to handle more calories and fluid," it continued. This fact, along with the knowledge that how I fuel directly affects how well I'll be able to train, told me I needed some tips from the pros on exactly how to eat to train my best. (Related: How to Stay Hydrated When Training for an Endurance Race)

The U.S. Olympic Committee put me in touch with Shawn Hueglin, Ph.D., R.D., a sports dietitian and physiologist who gave me a few important tips about how I should best fuel my body to train and perform as well as possible. I also consulted Michelle Portalatin, an ITCA-certified triathlon coach, to get all information I could about how to form a marathon training diet.

The main thing I learned was to avoid empty calories and focus on eating foods that give me the most nutrients per calorie. These include good sources of whole grains and starches (like brown rice, quinoa, sweet potatoes, oatmeal, barley, amaranth, millet, and rye), lean proteins (I'm a pescatarian, so my lean protein sources will come from fish, Greek yogurt, eggs, and beans), healthy fats (avocados, nuts, and olive oil), and of course all of the whole, colorful fruits and veggies I can get my hands on to provide antioxidants, vitamins, and minerals.

Of course, this sounds a whole lot like a recommendation for anyone striving to maintain a healthy diet, so I dug a little deeper to see what makes a certain diet good or bad specifically for runners. Ahead, the marathon training diet rules I followed.

Master the Timing and Frequency of Fueling

As with most things involving nutrition, the timing and frequency of eating during my training months is all about balance: I don't want to run on empty and suffer through tired, underperformed runs, but I also don't want a full stomach of food jostling around while I'm putting in my miles.

One to two hours before runs, Portalatin recommends eating a light, energizing meal or snack. In a pinch, a veggie juice 30 minutes before a workout works as well, she says. The rest of the day, Hueglin says to eat small meals every three to four hours to keep energy up and going. Eat adequately during the day, and you don't have to fuel before, during, and after every training session. Instead, Hueglin suggests evaluating how much I've eaten, if I'm truly hungry (and not just rewarding myself for a training session well-done) and how hard my training session really was to determine if I actually need to refuel and exactly when. (Related: The Best Foods to Eat Before & After Running a Marathon)

How to Find a Good Balance of Nutrients

As for specific carb, fat, and protein needs, Hueglin says that if I were starting a regimen that was drastically different from what I had been doing (say, going from six days of yoga to six days of running), I should bump up my carbohydrates just a bit, but the levels of fat and protein shouldn't need to change. Even so, I've always struggled getting adequate amounts of protein in my diet, so I've made it a personal goal to incorporate more lean protein (especially fish) in my meals and kept my carb consumption as it has been.

With this guidance, I've mapped out a marathon training diet. I'll be making a point to eat small meals every three to four hours during the day that include a healthy balance of carbs, fats, and especially lean protein from foods that give me the most nutrients per calorie during the week. The weekends will be my time to splurge if I really want to, but only to a small degree and in the case that it doesn't affect my training. For pre- and post-workout snacks, I'll be reaching for fruit and vegetable smoothies, healthy (meaning not a ton of sugar and full of natural ingredients) granola bars, fruit, nuts, and Greek yogurt. My other focus will be on making sure I'm fueling myself when I need it and not when I think I should, per Hueglin's suggestion, and making sure I'm listening to my body so that I can really survive those long runs.