From what to eat before mile one to what to skip entirely, sports dietitians break down the complete guide to running nutrition.
The question of what to eat as a runner sounds deceptively simple — carbs, hydration, maybe energy gels — until you’re several weeks into a training block wondering why your legs feel like lead and your stomach has staged a revolt by mile eight. Fueling is both a science and a deeply personal experiment, and the stakes are higher than most runners want to admit. Getting it right starts long before the starting gun fires, which means the hours before a run are not passive.
Most runners spend months perfecting their form, their splits, and their gear. Their nutrition strategy, by contrast, often gets improvised — a banana here, a gel there, a prayer that the stomach holds. The science of running fuel is more precise than that, and the consequences of getting it wrong show up fast and inconveniently. Here is what vetted sports dietitians actually say, sourced and confirmed.
The day before is more important than race morning
Pre-race fueling does not begin with breakfast. Kim Lowry, a dietitian at Houston Methodist and an experienced marathon runner herself, makes the case that the day before is where the real nutritional work happens. “Fueling your body for a marathon is important, but not all nutrients are created equal,” says Lowry. “In addition, the timing of your meals matters, too.”
Her framework centers the biggest carbohydrate load at lunch, not dinner. “You want to eat a lot of carbs the day before running a marathon,” says Lowry. “And you want to get most of them during lunch.” A large lunch built around roughly 80 percent carbs — pasta or a burrito bowl heavy on rice — is her recommendation, followed by a dinner of the same foods at half the portion. The reasoning is physiological: “By carbo-loading at lunch, you’re able to saturate your muscles with the energy they’ll need the next day — but also give yourself plenty of time to digest everything so you don’t feel bloated in the morning,” explains Lowry. “Following that with a smaller dinner can help maintain adequate carb levels without making you feel full when you wake up.”
Race morning requires its own strategy. “As you sleep, your brain uses about one-third of the carbohydrates you have stored away,” explains Lowry. “Replenishing this supply before a race is important because carbs are your body’s primary fuel source while running a marathon.” Her recommendation: 60 grams of simple carbs three to four hours before the start, with some protein alongside to support muscle repair. Right before the gun fires, “About an hour before you start, have another 30 to 60 grams of simple carbs,” says Lowry. “I recommend something that’s very easily digestible, like an energy gel packet or energy chews.”
The foods that will wreck your run
Knowing what to avoid is as consequential as knowing what to eat. Runner’s stomach — the cramping, nausea, and urgent bathroom needs that derail races — is largely preventable, and the culprits are consistent.
The mechanics of running itself are part of the problem. “Just the simple mechanics of running are where the problems begin. Your body is moving up and down, sometimes rapidly — as is any food that’s in your stomach. It’s a lot of sloshing, shaking and jostling, which can lead to cramps, nausea or an urge to go,” says Lowry. Physiology adds to it: during a long run, blood is redirected away from the gut toward working muscles, slowing digestion significantly. Individual tolerance varies, too. “All of these factors can lead to your gut becoming distressed — especially if your body isn’t used to it or if you’ve fueled with the wrong foods. There can also be some variability in how one body handles this stress compared to another,” Lowry says.
The short list of foods to sideline: anything high in fiber or fat. “Foods that are high in fiber, such as broccoli and cauliflower, and/or high in fat are harder for your body to break down — making them more likely to just sit and slosh in your stomach during a long run,” explains Lowry. “You’ll also want to avoid foods and medications that can potentially irritate your gut.” That includes alcohol, caffeine, spicy foods, and NSAIDs like ibuprofen. On race morning specifically, “Just make sure you avoid high fiber and high fat foods the morning of the race,” warns Lowry. “These take longer to digest and can cause bloating or gastrointestinal distress during your run.”
Dehydration accelerates all of it. “Having less water in your body means having less water to help move food through your gut. Plus, as you become dehydrated, your body pulls water from your stomach to help maintain blood volume levels — further stressing your gut. This is why preventing runner’s stomach is about more than just making good food choices, it’s also about starting a race well-hydrated and maintaining your hydration status as you run,” explains Lowry.
Mid-run fuel: gels and more
Once a run crosses the 60-minute mark, mid-run carbohydrates become essential. The goal is 30 to 60 grams per hour, and there are more ways to hit that target than most runners realize.
Registered dietitian Gabbi Berkow — certified in sports dietetics and based in New York — explains to the Peloton blog the core principle behind what works mid-run: fast-digesting carbs are “low in fat and fiber, so they convert to blood glucose quickly.” She also recommends pairing carbs with a small amount of protein, noting that quick-digesting protein will help to “keep your blood sugar stable and prevent muscle breakdown.” The overall payoff is clear: “Keeping your glycogen up enables continued exercise performance, delays fatigue, and keeps blood sugar stable,” Berkow says.
Whole food options are more viable than many runners assume. Kelly Jones, a Philadelphia-based registered dietitian and sports dietitian for athletes and active adults, makes the case for dates, raisins, and honey, also telling Peloton that they “may be just as successful at maintaining performance during longer-term exercise. They’re higher in nutrients and tend to be more cost-effective.”For something more substantial, she points to mashed potato pouches: “if you have the time, mashed potato and sweet potato pouches have been found to be effective” during a long run. For runners who do rely on packaged products daily, Jones adds an important distinction: “I tend to recommend more natural products when possible, especially when runners are using them in daily training and they make up a larger part of someone’s calorie intake over the course of a week versus someone who is just using them for long runs once per week.”
Hydration mid-run is inseparable from fueling. “In addition, it’s really important to take in fluid as you re-fuel, since fluid helps achieve both absorption and digestion of food,” adds Lowry.
Train your gut the way you train your legs
Every expert arrives at the same conclusion: nothing about race-day nutrition should be a surprise. The gut adapts to the stress of running, but it needs repetition and time. “Everyone’s stomach reacts differently to a long run, and even simple carbs can give some people grief at first. Well before race day, be sure to give your body the time it needs to adjust to digesting food during exercise, as well as plenty of time to try out different foods in case your gut is more sensitive,” says Lowry. Her rule of thumb: only use foods on race day that you have tested and practiced with at least three or four times in training.
The payoff for doing this work early is consistency when it counts. As Lowry puts it: “I recommend energy gel or energy chews for refueling. They’re not only easy to carry on the go, but they’re typically designed to deliver simple carbs in a way that can help limit the chance of GI distress.”
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