During an ultra marathon, you should aim to eat 200 to 300 calories per hour, mostly from carbohydrates, starting early in the race and continuing consistently until the finish. Your body burns 600 to 1,000 calories per hour while running, but your gut can only absorb a fraction of that. The goal isn’t to replace every calorie. It’s to keep your energy stable, your stomach calm, and your muscles fueled enough to keep moving.
How Many Carbs Per Hour
Carbohydrates are the primary fuel your body can access quickly during running. The standard recommendation for events longer than three hours is 90 grams of carbohydrates per hour, which works out to roughly 360 calories from carbs alone. Most ultra runners in practice consume closer to 60 grams per hour, and that’s a reasonable starting point if you haven’t trained your gut for higher intake.
There’s growing evidence that pushing intake even higher can help. A study on elite mountain marathon runners found that consuming 120 grams of carbohydrates per hour reduced markers of muscle damage compared to 60 or 90 grams per hour. But those runners had done specific gut training beforehand to tolerate that volume. If you haven’t practiced eating that aggressively during long training runs, jumping to 120 grams per hour on race day is a recipe for nausea. Start at 60 grams per hour and build up over weeks of training.
Your body absorbs roughly one gram of carbohydrate per minute from a single sugar source like glucose. You can increase that ceiling by combining glucose with fructose, which uses a separate absorption pathway. This is why most sports drinks and gels use a glucose-fructose blend.
Best Foods at Aid Stations
The beauty of ultra marathons compared to shorter races is that you’re moving at a pace where real food becomes not just possible but preferable. After hours of gels and sweet drinks, your palate will revolt, and savory whole foods become genuinely appealing. Here’s what you’ll typically find at aid stations and why each option works.
Salted potatoes are one of the best all-around choices: two or three small potatoes deliver about 100 calories, 25 grams of carbs, and 500 to 1,000 milligrams of sodium. They’re easy to chew, easy to digest, and give your taste buds a break from sweetness. Potato chips offer a similar savory hit with about 130 calories, 15 grams of carbs, and 260 milligrams of sodium per handful.
For quick sugar, gummy bears (130 calories, 31 grams of carbs per handful) and bananas (100 calories, 27 grams of carbs) are reliable standbys. Bananas do contain about 3 grams of fiber each, so go easy if your stomach is already unhappy. Watermelon is a favorite in hot races because it’s about 92% water, providing hydration alongside 60 calories and 16 grams of carbs per cup, plus potassium for muscle function.
When you need sodium specifically, pickles are hard to beat: a single spear has 280 milligrams of sodium with almost no calories. Warm broth is another sodium bomb at roughly 750 milligrams per cup, and it’s one of the few things that feels good during cold nighttime miles. Pizza rolls (100 calories, 13 grams of carbs, 190 milligrams of sodium for three pieces) combine carbs and sodium in one easy package.
Flat Coke is the unofficial fuel of late-race ultra running. A flask delivers around 200 calories and 52 grams of highly digestible carbs. Let it go flat first if you can, because carbonation can cause bloating and stomach trouble when you’re already running on a stressed gut.
Solid Food vs. Liquid Calories
Early in a race, when your pace is higher and blood flow to your digestive system is more limited, liquid and semi-solid calories (gels, sports drinks, soft foods) tend to sit better. As you slow down in later miles, your gut can handle more substantial food. Many experienced ultra runners shift from gels and drinks in the first few hours to real food like potatoes, sandwiches, and broth as the race progresses.
One caution with liquid calories: highly concentrated carbohydrate drinks can actually cause more stomach problems than solid food. Solutions with high sugar concentration draw water into the intestines and are a primary nutritional cause of GI distress during endurance events. If you’re relying on caloric drinks, dilute them more than the label suggests and alternate with plain water. Research on elite 24-hour runners found that even at very high calorie intakes, GI episodes were transient and manageable, but these were athletes who had trained their guts extensively.
Sodium and Electrolytes
Sodium is the electrolyte that matters most during an ultra. You lose it steadily through sweat, and if blood sodium levels drop too low, you risk hyponatremia, a potentially dangerous condition that causes confusion, nausea, and in severe cases, seizures. The recommended intake is 300 to 600 milligrams of sodium per hour during prolonged exercise.
How much you personally need depends on your sweat rate, the temperature, your body size, and how salty your sweat is. Some runners lose more than a liter of sweat per hour in hot conditions, while others sweat far less. Pay attention to fluid intake first. Drinking too much plain water without adequate sodium is actually a more common cause of hyponatremia than simply not taking enough salt. Pair your water with salty foods or electrolyte drinks rather than chugging water by itself at every aid station.
Hydration Without Overdoing It
Sweat rates during exercise range from about half a liter to four liters per hour, depending on intensity, heat, humidity, and your individual physiology. There’s no single number for how much to drink. The most reliable approach is to drink to thirst rather than forcing a fixed schedule.
Research on ultra runners has found that drinking more than thirst dictates doesn’t improve performance and may actually hurt it. A study of elite 24-hour runners showed a negative relationship between total water intake and distance covered, suggesting that overhydration is inefficient regardless of whether it causes hyponatremia. In hot conditions above 25°C (77°F), your thirst drive increases naturally, which helps guide intake upward when you need it. Carry a handheld bottle or use a hydration vest so you can sip consistently rather than binge-drinking at aid stations.
Caffeine for Late-Race Fatigue
Caffeine is one of the most effective legal performance aids for endurance running, improving performance by 2 to 7% at doses of 3 to 6 milligrams per kilogram of body weight. For a 70-kilogram (154-pound) runner, that’s roughly 200 to 400 milligrams, equivalent to two to four cups of coffee.
In an ultra, the strategic move is to save caffeine for when fatigue really sets in, typically the second half of the race or during nighttime hours. If you consume caffeine regularly in daily life, it will still work, but the effect may be slightly blunted. Taking it about an hour before you expect to need the boost gives it time to peak in your bloodstream. Coke, caffeinated gels, and caffeine pills are the most common delivery methods on course. Start with a lower dose and add more later rather than taking a large amount at once, which can cause jitteriness or stomach upset on an already stressed system.
The Low-Carb Alternative
Some ultra runners follow a low-carbohydrate, high-fat diet and rely more heavily on fat burning during races. There’s real science behind this approach: athletes who adapt to a low-carb diet for six months or longer can burn fat at rates of about 1.5 grams per minute, roughly double the rate of carbohydrate-adapted athletes. They also sustain fat burning at higher exercise intensities, up to around 70% of maximum effort compared to 55% for high-carb athletes.
The catch is that fat oxidation drops to nearly zero above 90% of maximum effort. Ultra marathons are mostly run at moderate intensity where fat burning works well, which is why this approach has gained traction specifically in the ultra community. But if you need to push hard on a climb or surge to make a cutoff, you’ll still need carbohydrates. Most fat-adapted ultra runners carry some carbs for these moments while relying on fat metabolism for the steady-state miles. Switching to a low-carb strategy requires months of adaptation. Doing it for the first time a few weeks before a race will impair performance and leave you feeling terrible.
Preventing Stomach Problems
GI distress is one of the top reasons ultra runners slow down or drop out. There are four main triggers: reduced blood flow to the gut during exercise, the mechanical jostling of running, psychological stress, and nutritional choices. You can’t eliminate the first three, but you have significant control over the fourth.
Avoid high-fiber, high-fat, and high-protein foods in the 24 hours before and during the race. These slow digestion and sit in your stomach. Some runners benefit from reducing FODMAPs (fermentable carbohydrates found in foods like onions, garlic, wheat, and certain fruits) in the days before a race, though this diet is restrictive enough that it’s worth trying in training first.
The single most effective strategy is gut training. Your digestive system adapts to processing food during exercise just like your muscles adapt to running. Practice eating during your long training runs, using the same foods and drinks you plan to use on race day. Increase the volume gradually over weeks. Runners who train their gut to handle higher carbohydrate loads report fewer GI symptoms and can fuel more aggressively when it counts.