Stomach pain can make the recommended 60–90 grams of carbohydrate per hour feel impossible during marathon long runs. The answer is usually not to force down more gels at once. To train your gut for 60–90g carbs per hour, build intake gradually, use a carb format you tolerate, and match concentrated fuel with enough fluid. This matters even more when low energy availability or RED-S is a concern: consistently under-fueling training can make recovery and performance harder, not easier.
Quick Answer
Start at the highest carbohydrate intake you can complete comfortably, even if that is only 30–45g per hour. Practice that amount on one long run each week, then increase by roughly 10–15g per hour after one or two comfortable sessions.
Split fuel into small, regular doses rather than taking a large gel only when you feel tired. Most runners do best with 15–25g every 15–20 minutes, plus fluids taken steadily according to thirst, weather, and sweat loss.
For a 60–90g-per-hour target, use mixed carbohydrate sources when possible. Products containing glucose or maltodextrin plus fructose can increase carbohydrate absorption compared with glucose alone, but the mix still needs practice. A product that works in a short race can cause trouble after two hours if you have never used it in training.
Why This Happens
Your stomach and intestines are working while blood flow is being prioritized for exercising muscles and skin cooling. Running jostles the gut, heat adds stress, and a hard pace can slow stomach emptying. Add a very sweet gel, too little water, or a large bolus of fuel, and the concentration in your stomach may be high enough to trigger cramping, nausea, sloshing, or an urgent bathroom stop.
The 60–90g-per-hour recommendation is not a compulsory starting point. It is a performance-oriented range commonly used for longer endurance events, especially when running lasts beyond about two and a half hours. Your useful target depends on duration, pace, intensity, body size, what you ate beforehand, and what you can absorb comfortably.
Gut training is partly physical adaptation and partly routine learning. Repeatedly consuming carbohydrate during exercise teaches you how to pace intake, which textures work, how much water your preferred fuel needs, and whether a problem comes from the product, the dose, the pace, or the conditions.
RED-S concerns change the context. Frequent stomach upset may coexist with restrictive eating, skipped recovery meals, or training on too little overall energy. A gut plan cannot replace adequate daily fueling. If you suspect low energy availability, recurrent illness, stress fractures, missed periods, low libido, unusual fatigue, or declining performance, speak with a sports physician or registered sports dietitian.
Step-by-Step Method
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Set a tolerable baseline. On your next long run, use an amount that feels manageable from start to finish. For many runners, that is 30–45g per hour. Record the product, grams per hour, water, weather, pace, and symptoms. Do not test several new variables in one run.
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Fuel early, not after a crash. Begin around 20–30 minutes into the run. Waiting until you feel depleted often leads to taking too much too quickly. A simple starting schedule is 20g every 20 minutes, which equals 60g per hour.
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Increase one small step at a time. After one or two symptom-free long runs, add 10–15g per hour. For example, move from 45g to 55–60g, then to 70g, then toward 80–90g only if your event and pace justify it. Hold the dose steady longer if symptoms appear.
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Choose a format you can take calmly. Gels are convenient but not mandatory. Sports drink, chews, liquid carbohydrate, bananas, low-fiber bars, or a gel-and-drink combination can all work. If gels feel heavy, try a more fluid option or divide one gel into smaller portions over several minutes.
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Pair fuel with sensible fluid intake. Follow the instructions on the product first. A gel is usually easier on the stomach with several mouthfuls of water, while a carbohydrate drink already contains water and should not automatically be chased with a large volume. Avoid drinking huge amounts all at once; steady sips are usually easier to tolerate.
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Practice at realistic intensity. Easy long runs are useful, but your marathon fueling plan also needs testing during marathon-pace segments. Many runners tolerate 70g per hour easily while jogging, then struggle at race pace in warm weather. Add fueling practice to selected race-specific sessions, not every hard workout.
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Simplify the 24 hours before key long runs. Keep pre-run meals familiar. Limit unusually high-fiber, high-fat, spicy, or sugar-alcohol-heavy foods if they commonly upset your stomach. This is not a reason to undereat; it is a reason to choose easy-to-digest carbohydrate and enough fluid before demanding sessions.
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Use a symptom rule. Mild fullness that settles is different from escalating pain, nausea, or diarrhea. If symptoms build, reduce the next trial by one step, slow the intake pattern, check fluid timing, and review pace and heat. Do not repeatedly force an intake level that causes significant pain.
Common Mistakes
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Jumping from minimal fuel to 90g per hour. Your gut gets overwhelmed, especially when the carbohydrates come from several gels taken close together. Instead, build from your current successful dose in small increments.
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Taking gels without enough water. Thick, concentrated fuel can sit heavily in the stomach. Instead, take gels with water in small, regular sips unless the product instructions say otherwise.
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Using only race day for testing. New gels, drink powders, caffeine doses, and breakfast choices create avoidable uncertainty. Instead, rehearse the same plan during long runs and race-pace workouts.
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Blaming the fuel when the pace is too hard. A pace above sustainable effort, especially in heat, can be the main driver of nausea. Instead, review effort, temperature, and hydration before abandoning a fueling strategy.
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Confusing under-fueling with a sensitive gut. Starting a long run underfed can lead to panic eating later, which often causes discomfort. Instead, eat a familiar carbohydrate-focused pre-run meal and begin fueling early.
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Adding high doses of caffeine during gut training. Caffeine can help some runners but can also worsen urgency or nausea. Instead, establish carbohydrate tolerance first, then test caffeine separately.
Checklist or Decision Table
| Problem during long runs | Likely contributor | Practical adjustment for next run |
|---|---|---|
| Heavy, sloshy stomach | Large drinks or big fuel boluses | Take smaller sips and split fuel into 15–20 minute doses |
| Cramping after gels | Concentrated gel with too little water | Take each gel with water or switch part of intake to sports drink |
| Nausea late in the run | Heat, hard pace, accumulated intake | Slow slightly, cool down, hold the current carb dose before increasing |
| Energy crash, then overeating | Fuel started too late | Begin at 20–30 minutes and use a timer alert |
| Diarrhea or urgency | Caffeine, sugar alcohols, fiber, unfamiliar food | Simplify pre-run food and test a lower-fiber, caffeine-free fuel option |
| Symptoms above 60g per hour | Dose increased too quickly or single-source intake | Hold at the last comfortable dose and trial mixed-carb products gradually |
Before each long run, check: familiar breakfast, familiar fuel, a planned grams-per-hour target, water access, and a timer or watch reminder. Afterward, note what happened before changing the plan.
When This Advice Does Not Apply
This gradual approach is for ordinary exercise-related stomach discomfort, not severe or persistent symptoms. Stop the session and seek medical advice promptly for severe abdominal pain, fainting, vomiting that prevents fluid intake, blood in stool, black stools, chest pain, or signs of significant dehydration.
Also, do not assume every stomach issue is a fueling problem. Ongoing gastrointestinal symptoms outside running, unexplained weight changes, repeated stress injuries, menstrual disruption, or persistent fatigue deserve assessment from a qualified clinician. Runners with diabetes, diagnosed digestive conditions, or a history of eating disorders should individualize carbohydrate and hydration plans with appropriate medical or sports nutrition support.
Finally, 90g per hour is not necessary for every runner or every long run. If you are running for under two hours, completing an easy aerobic session, or racing at an intensity where a lower intake performs well, a smaller amount may be more practical.
Realistic Example
A marathon trainee currently manages one 25g gel per hour but develops cramps when attempting three gels per hour. On a two-hour easy long run, the runner starts with 20g at 25 minutes, then takes 20g every 20 minutes with a few mouthfuls of water. That reaches 60g per hour without needing a large dose at once.
After two comfortable runs, the runner keeps the same schedule but replaces one 20g serving with a 30g mixed-carbohydrate drink portion, reaching about 70g per hour. The following race-specific workout is warmer and includes marathon-pace blocks, so the runner stays at 70g instead of increasing. That decision provides useful information: the dose is workable, but heat and intensity still raise the gut challenge. The next progression can wait for cooler conditions or an easier long run.
Final Takeaway
The best way to handle 60–90g of carbs per hour is to treat it as a trainable skill, not a test of toughness. Start with the highest amount you tolerate, take small doses early and regularly, pair concentrated fuel with appropriate fluid, and change only one variable at a time.
For marathon runners with RED-S concerns, the wider goal is adequate energy intake across the full training week. A successful long-run fueling plan should support performance without creating pain, fear around food, or a recovery deficit.
FAQs
How long does it take to train your gut for 90g of carbs per hour?
Most runners need several weeks of consistent long-run practice to tolerate 90g of carbohydrate per hour comfortably. A realistic progression is to practice once weekly, holding each new intake level for one or two symptom-free sessions before adding another 10–15g per hour. Some runners adapt faster, while others perform best below 90g per hour. The goal is not reaching a headline number; it is finding the highest intake that supports your pace without escalating nausea, cramps, or bathroom urgency.
Can I reach 60g of carbs per hour using only gels?
Yes, you can reach 60g per hour using only gels if you tolerate their texture and take them with suitable water. Two 30g gels per hour, or three 20g gels per hour, are common approaches. The important detail is timing: spread each serving across the hour rather than taking multiple gels together. If gels repeatedly cause stomach pain, do not force them. Replacing one gel with sports drink, chews, or a liquid carbohydrate option may lower the perceived heaviness while keeping the carbohydrate target similar.
Should I drink water with every energy gel on a marathon long run?
Usually, yes, taking a gel with water is a sensible starting point unless the product is specifically designed to be consumed without it. Water helps dilute concentrated carbohydrate in the stomach and can reduce the heavy, sticky feeling that some runners get from gels. You do not need to chug a full bottle each time. Several comfortable mouthfuls are often enough, adjusted for heat, sweat rate, and the product directions. If you use a carbohydrate sports drink, avoid adding excessive water solely by habit.
Why do I get stomach cramps only when I run at marathon pace?
Marathon pace can cause cramps because harder running reduces the margin your gut has for digestion and increases mechanical jostling. Heat, stress, and shallow breathing can compound the effect. A fueling amount that feels easy during a relaxed long run may therefore feel excessive during sustained marathon-pace work. Test your plan in race-specific workouts, but do not raise both pace and carbohydrate intake on the same day. First confirm the dose at easy pace, then repeat it at marathon pace before progressing further.
Is 90g of carbs per hour necessary for a first marathon?
No, 90g of carbs per hour is not necessary for every first marathon. It can be useful for runners who will be out for several hours and can tolerate it, but a reliable lower intake is better than an ambitious plan that causes stomach distress. Many first-time marathoners do well starting around 45–60g per hour and adjusting through training. Consider duration, expected pace, weather, and what you have repeatedly practiced. The best race plan is one you can execute calmly from the first hour to the finish.
What should runners with RED-S concerns do if fueling causes anxiety or pain?
Runners with RED-S concerns should get individualized support if fueling causes anxiety, persistent pain, or pressure to restrict food. A sports dietitian and physician can help assess overall energy availability, digestive symptoms, training load, and recovery needs without treating carbohydrate intake as a willpower problem. For immediate training, keep the plan predictable: use familiar foods, start with a tolerable amount, and avoid compensating by skipping meals before or after runs. Persistent fatigue, recurrent injuries, menstrual changes, or worsening performance are important reasons to seek professional assessment.