How Many Carbs Per Hour Do You Need for an Ultramarathon?

For a 50K, aim for roughly 60 to 90 grams of carbohydrate per hour. The effort is close to a marathon and the day is short enough that you can run high. A 50 miler holds that same 60 to 90 g/hr, just over a much longer day, so you add in real food to keep your stomach and your taste buds working. For a 100 miler most runners settle into about 45 to 80 g/hr, because you are moving slower on average and the rate has to last a full day and night. The pattern is simple. Shorter and faster races earn you a higher hourly number, and longer and slower races give some of that rate back for the sake of staying sustainable and keeping your gut happy.

For most ultrarunners 60 to 90 g/hr is the proven, well-tolerated target, and honestly it is plenty. The 120 g/hr number comes from research on trained athletes using a glucose-plus-fructose mix, where a trail-marathon study found 120 g/hr cut muscle damage and improved recovery against 60 and 90 g/hr. So 120 g/hr is real and it is backed by evidence, but it needs a multi-transportable carb mix and a gut you have trained for months. Treat 60 to 90 g/hr as the goal. Only chase 100 to 120 g/hr if you are racing fast, your stomach can take it, and you have rehearsed it. More carbs only help if you can absorb them.

Read the carb grams on each label and add them up to your hourly target. A typical energy gel is about 22 to 25 g of carbohydrate, a serving of chews (3 to 4 pieces) is roughly 24 g, and a scoop or bottle of drink mix runs about 30 to 60 g depending on whether it is a standard or high-carb formula. So 60 g/hr is roughly two and a half gels, or one strong bottle plus a gel. 90 g/hr is about four gels, or two bottles plus a gel. To hit 120 g/hr you almost always need high-carb drink mix, because you cannot comfortably chew that much solid food. Build the hour out of a mix of liquid and solid so no single source has to do all the work.

Field studies of real races keep finding average intakes well below the recommendation, often around 30 to 45 g/hr, and some runners as low as 22 g/hr. The reasons are not mysterious. Appetite drops on long efforts, a jostled stomach takes less, flavor fatigue sets in, you forget to eat on climbs and technical descents, and a lot of runners simply never trained their gut to handle more. And it matters, because the same studies show the finishers and the faster runners eat more. Elite finishers average around 70 g/hr while non-finishers often eat under 45 g/hr. Underfueling is one of the most common reasons ultras fall apart, and it is also one of the most fixable. The fix is a written hourly plan plus gut training.

Carb use tracks intensity, so the faster and harder you run, the more carbohydrate you burn per hour and the more you should take in. On runnable, higher-effort sections, lean toward the top of your range. On long power-hiking climbs and slow technical terrain your effort and your carb burn drop, so it is fine to ease the rate a little, and your stomach will thank you, because hard efforts blunt digestion. Here is a simple rhythm for mountain courses. Fuel hard on the runnable flats and the downhills where your gut can actually process food, and at least keep sipping carbs on the steep hikes instead of going to zero.

Glucose and fructose go through different intestinal transporters. Glucose uses SGLT1 and fructose uses GLUT5. Because they do not compete, taking both lets your gut absorb more total carbohydrate than glucose alone, which maxes out around 60 g/hr. Up to about 90 g/hr a 2:1 glucose-to-fructose ratio works well. To push toward 120 g/hr the research points to a 1:0.8 glucose-to-fructose ratio as the better blend, because the extra fructose capacity unlocks higher total absorption with less GI distress. Most modern high-carb sports products are already mixed near these ratios, so check the label for a glucose-fructose or maltodextrin-fructose blend if you plan to fuel high.

Carbohydrate gives you about 4 calories per gram, so multiply your carb target by 4. That puts 60 g/hr at about 240 cal/hr, 90 g/hr at about 360 cal/hr, and 120 g/hr at about 480 cal/hr. A lot of ultrarunners think in calories and aim for roughly 200 to 400 cal/hr depending on body size, pace, and conditions, which is the same 50 to 90 g of carbohydrate. If you are also taking in some fat or protein from real food late in a long race, count those calories on their own, but keep carbohydrate as the engine, because it is what your working muscles can actually use fast.

Generally yes. Body size matters, so a smaller runner can aim at the low end of the range and a larger runner the high end, which is why planning off body weight beats one number for everyone. That said, gut absorption is trainable and not strictly tied to body mass, so a smaller, well-trained athlete can still run 90 g/hr. For female runners specifically, fluid needs are often lower because of smaller body size and lower sweat rates, and there is a higher hyponatremia risk from drinking too much plain water relative to body mass, so pairing carbs with enough sodium matters. Gut training also tends to be harder during the luteal phase when GI sensitivity is higher, so practice fueling across your cycle. The honest answer is to make it personal. Start from a per-bodyweight target, then train it up.