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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsThe most reliable way to fuel long runs without nausea, cramps, bloating or urgent bathroom stops is to build and rehearse an individual plan. Start with a tolerable carbohydrate amount, use familiar products and drinks, and change only one variable at a time. For marathon-length efforts, the 2019 World Athletics consensus gives 60–90 grams of carbohydrate per hour as a target range, but the upper end is not mandatory and should be reached only if your gut has been trained to tolerate it.
How much carbohydrate do you need?
Duration is the first decision. World Athletics’ 2019 consensus recommends 30–60 grams of carbohydrate per hour for events lasting 1–2.5 hours and up to 90 grams per hour for efforts longer than 2.5 hours. For marathon running, it describes 60–90 grams per hour as a target range that must be adjusted for pace, available opportunities to eat and drink, and personal tolerance.
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These are planning ranges, not a requirement that every runner immediately consume 90 grams per hour. If you have never fueled during runs, a lower starting intake is sensible while you learn what your stomach accepts. A personalized, practiced plan matters more than copying another runner’s number.
| Run or race duration | Carbohydrate guidance | How to apply it |
|---|---|---|
| 1–2.5 hours | 30–60 g/hour | Choose a dose you can repeat without symptoms, then adjust during training. |
| More than 2.5 hours | Up to 90 g/hour | The higher end requires practice and is not appropriate for everyone. |
| Marathon training or racing | 60–90 g/hour target range | Individualize for pace, course access, weather, fluid plan and tolerance. |
For example, a 60-gram-per-hour plan over a three-hour effort requires 180 grams in total. Divide that total into the number of servings you can carry and comfortably take, rather than waiting until you feel empty. The arithmetic is simple; deciding what your stomach can absorb while running is the part that requires repeated practice.
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The 35 ± 26 grams per hour reported in the marathon subgroup of Costa and colleagues’ 2011 observational event study is a description of what those athletes consumed, not a recommended target. It should not be used to replace the newer World Athletics guidance.
Why fueling causes stomach problems
Running changes gastrointestinal conditions at the same time you are asking your gut to digest and absorb fuel. Symptoms can include nausea, fullness, reflux, cramping, bloating, flatulence, diarrhea or an urgent need for a toilet. The response varies substantially between athletes and can worsen as an event progresses.
Do not assume that one ingredient is always responsible. The 2019 distance-running review recommends balancing the benefit of fluid and carbohydrate against practical opportunities, cost and the risk of gut discomfort. Your total dose, concentration, timing, fluid volume, pace, heat and personal history can all matter.
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Burke, Jeukendrup, Jones and Mooses summarized the practical trade-off in their 2019 distance-running review: “A personalized and practiced race nutrition plan should balance the benefits of fluid and CHO consumed within practical opportunities, against the time, cost, and risk of gut discomfort.” That means the best plan is the one you can afford, carry, access and tolerate at your intended pace.
Before a long run
Use a familiar carbohydrate-rich meal
Eat foods you have already tolerated rather than experimenting before a key workout. The evidence supports carbohydrate-rich eating before competition in broad terms, but it does not establish one universal meal or a single digestion window for every runner. Your own training log is more useful than a rigid menu.
Allow enough digestion time
Give the meal time to settle according to your normal routine. A large meal immediately before running is more likely to feel uncomfortable than a familiar meal eaten with adequate time, but the correct interval depends on portion size, food choice and individual tolerance.
Change one thing at a time
Do not introduce a new breakfast, a new gel, a new drink and a faster pace in the same session. If symptoms appear, you will not know which change caused them. Keep the pre-run meal, product and timing stable while you evaluate your during-run plan.
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Protect key sessions
Test new strategies on an ordinary long run rather than the final rehearsal or a race. Have a backup route with toilet access when you are evaluating a new dose. This does not eliminate symptoms, but it reduces the cost of an unsuccessful experiment and gives you useful information without sacrificing an important workout.
Build your during-run plan step by step
1. Set a starting carbohydrate target
Estimate the planned duration and select a conservative point within the relevant range. A runner new to fueling may begin near the lower end of the guidance, then increase on later long runs if symptoms remain controlled. The goal is a repeatable intake, not the largest number you can force down once.
2. Convert the target into servings
Check the carbohydrate grams on the nutrition label of the product or drink you intend to use. Divide your hourly target into small, regular servings instead of waiting until you feel depleted. Record the grams per serving and the planned time of each dose so you can repeat the session. If a serving contains 25 grams and your hourly target is 50 grams, two servings per hour is the basic calculation; the spacing and fluid pairing still need testing.
3. Decide how much fluid accompanies each dose
Some concentrated products are designed to be taken with water; a carbohydrate drink supplies both fuel and fluid. Follow the product’s stated directions, then test the combination at your training pace. A dose that works with adequate water may feel very different when taken dry or followed by only a small sip.
4. Schedule practical opportunities
Place intake where you can actually reach it: before a climb, at a planned bottle point, or at a course aid station. World Athletics emphasizes balancing nutrition with drinking opportunities and the realities of the route. A theoretically perfect schedule that you cannot carry or access is not a useful race plan.
5. Repeat the exact combination
Use the intended race fuel and drink on multiple long runs. Practice opening packaging, carrying enough servings and taking them while running. Familiarity reduces last-minute decisions and reveals whether symptoms are related to the product, timing, concentration or fluid plan.
6. Review the run before changing the plan
After each session, write down planned and actual carbohydrate grams per hour, the time of each serving, fluid volume, weather, pace, duration and symptoms. Note whether you finished the run, slowed down, skipped a dose or needed a bathroom. A plan that looks good on paper but repeatedly fails at a certain pace or temperature needs adjustment.
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Progressively train your gut
Gut training means practicing carbohydrate intake repeatedly so your body and routine become accustomed to processing it during exercise. The 2025 systematic review of GI interventions identifies gut training as promising, but its abstract does not establish a guaranteed protocol or a symptom-free outcome.
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- Start below your final target. Pick an amount you can tolerate during an ordinary long run.
- Repeat before increasing. Use the same product, timing and fluid combination on more than one session.
- Increase one variable. Add carbohydrate, shorten the interval between doses, alter concentration or change the format—not all at once.
- Test at race-like intensity. A plan tolerated at an easy pace may feel different when you run near marathon pace.
- Keep a symptom log. Note pace, duration, weather, food, carbohydrate grams, fluid, caffeine and symptoms. Look for patterns over several runs rather than blaming one episode.
If a change causes problems, return to the last tolerated version and hold it steady. You can progress again later with a smaller adjustment. There is no requirement to reach 90 grams per hour if a lower amount lets you run consistently and avoid distress.
Choose the format your stomach and logistics tolerate
Gels, chews or confectionery, and carbohydrate drinks can all fit a sound plan. The reviewed evidence does not show one branded format is universally superior. Compare the factors that affect your own run.
| Format | What to compare | Potential practical issue |
|---|---|---|
| Carbohydrate drink | Carbohydrate per bottle, concentration, fluid volume and whether the course supplies the same mixture | Carrying enough liquid can add weight; a stronger mixture may be harder to tolerate. |
| Gel | Carbohydrate per sachet, carbohydrate sources, texture, water requirement and packaging | A concentrated dose may feel heavy without sufficient water; opening it while running takes practice. |
| Chews or confectionery | Carbohydrate per piece or serving, chewing ease, texture and packaging | Chewing can be awkward at high intensity, and portions must be counted accurately. |
The 2022 systematic review comparing food with supplemental carbohydrate included 15 studies and 151 participants. It found no clear performance difference between food and supplemental carbohydrate in the included studies, but most exercise comparisons involved cycling rather than running. That limits how confidently the result can be applied to marathon training.
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Compare cost as well as comfort
Cost is part of a sustainable plan. Compare the price per serving and, more usefully, the price per gram of carbohydrate. A cheaper product that you cannot tolerate, cannot find on the course or must replace after every failed run is not necessarily economical. Include bottles, carrying belts, disposable packaging and the cost of buying an unfamiliar product at the race expo. If a sports drink will be supplied on race day, practicing with that exact mixture may reduce both expense and logistical uncertainty.
Match hydration to conditions instead of chasing a fixed number
World Athletics recommends a race-specific fluid plan that balances sweat losses, drinking opportunities and tolerance. Consider expected temperature, humidity, pace, access to bottles or aid stations, and whether your carbohydrate is already in the drink.
- Do not treat “drink as much as possible” as a universal rule.
- Do not assume you must replace every drop of sweat in every weather condition.
- Practice the volume and timing you expect to use in the race.
- Account for fuel concentration: adding powder or syrup to less water creates a stronger drink.
- Reassess the plan for hot races, cold races and courses with limited aid stations.
- Check whether taking a gel immediately before an aid station means you will have water available, or whether the next opportunity is too far away.
The American College of Sports Medicine’s 1996 position stand advised 30–60 grams of carbohydrate per hour during intense exercise lasting longer than an hour. That guidance is historical; newer distance-running recommendations provide the more relevant framework for marathon planning. Older specific fluid prescriptions should not be presented as universally current.
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Nausea or a heavy, sloshing stomach
- Review the total carbohydrate dose and drink concentration.
- Check whether you took a large amount at once instead of smaller servings.
- Compare the same product at an easier pace and at race-like pace.
- Test a different format while keeping the carbohydrate amount and fluid plan similar.
- Check whether you drank a large volume rapidly rather than taking smaller, regular sips.
Cramping or abdominal pain
- Record pace, heat, meal timing and the exact product used.
- Change only one factor on the next run.
- Stop or reduce intake if pain is severe, worsening or accompanied by other concerning symptoms.
Urgency, loose stools or diarrhea
- Review the pre-run meal and the timing of the last large intake.
- Check whether a new drink, gel or chew was introduced.
- Consider whether heat, dehydration, illness or an unusually hard pace coincided with the episode.
- Do not diagnose yourself from a single run; look for repeated patterns and seek clinical advice when symptoms persist.
Gas or bloating
The 2011 event study found an association between reported carbohydrate intake and flatulence, but it did not prove causation. Test dose, timing, concentration and format separately rather than assuming that all carbohydrate or one named ingredient is the culprit.
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When to abandon a test
Do not try to “train through” severe pain, repeated vomiting, faintness, bloody stool or signs of significant dehydration. End the session, address immediate safety and obtain medical advice. A minor, isolated symptom can be logged for later troubleshooting; a dangerous or escalating symptom should not be treated as a fueling experiment.
Should you try low-FODMAP diets, probiotics or hydrogel products?
The 2025 systematic review groups current research into gut training, carbohydrate mixtures, low-FODMAP approaches, hydrogel products and probiotics. Its abstract describes gut training as promising, but it does not justify presenting any of these interventions as a guaranteed fix or giving a universal prescription.
A restrictive diet can reduce food variety and may create nutritional problems if used without a clear reason. Probiotics and specialized products may help some athletes and not others. If you want to test one, change only that intervention, maintain a log and consider guidance from a qualified sports dietitian. Do not simultaneously switch your breakfast, carbohydrate dose, drink concentration and supplement, because that prevents a useful comparison.
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Food, gels or drink: which is best?
There is no single winning format for every marathoner. Solid food may be inexpensive and familiar but can be harder to chew at high intensity. Gels are compact and easy to count, yet often require planned water and may feel concentrated. Drinks combine carbohydrate and fluid, but carrying enough volume adds weight and the concentration changes when you alter the water amount.
Choose according to the course as well as your stomach. A product unavailable at aid stations may require carrying every serving. A course drink that you have never tested can create a problem even if it is popular with other runners. Read the label, calculate the grams supplied per hour, and rehearse the exact sequence of fuel and water at race pace.
Use a race-day checklist
- Write down your hourly carbohydrate target and the grams in each serving.
- Pack the exact products you practiced with, plus a realistic reserve.
- Confirm where water and sports drink will be available.
- Decide which servings you will take before aid stations, climbs or pace changes.
- Use the same pre-race meal and timing that worked in training.
- Do not increase to 90 grams per hour for the first time on race day.
- Adjust for heat, access and your actual tolerance rather than following a rigid number.
- Carry a written schedule or mark serving times on your wrist, bottle or watch if fatigue makes mental arithmetic difficult.
- Pack products so they can be opened with cold, sweaty hands and dispose of wrappers without dropping them.
When to get professional help
Consult a qualified sports dietitian or clinician if GI symptoms are persistent, severe, recurrent, interfere with training, cause dehydration, or occur with bleeding, fainting, fever or unexplained weight loss. A fueling article cannot diagnose gastrointestinal disease or replace medical evaluation.
Frequently asked questions
Should every marathon runner aim for 90 grams of carbohydrate per hour?
No. World Athletics lists 60–90 grams per hour as a marathon target range, with the upper end requiring practice and individual tolerance. A lower intake that you can consistently absorb is more useful than a higher intake that repeatedly causes symptoms.
How should a beginner start fueling long runs?
Begin near the lower end of the duration-appropriate range, use a familiar product or drink, and repeat it on several runs. Increase only one variable after you have established tolerance. Do not make the first high-dose test your race.
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Do gels always need water?
Not every product has identical instructions. Check the label and practice the stated fluid pairing. A concentrated gel taken without the water it was designed to accompany may feel very different from the same gel followed by adequate fluid.
Are real foods better than gels?
Neither is universally better. A 2022 review of 15 studies and 151 participants found no clear performance difference between food and supplemental carbohydrate, but most studies involved cycling. In running, choose the format you can tolerate, carry and access.
Can hydration alone prevent stomach problems?
No. Fluid plan, carbohydrate dose, concentration, pace, weather and personal history all interact. World Athletics recommends balancing sweat losses, drinking opportunities and tolerance rather than following a universal “drink as much as possible” rule.
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Will a low-FODMAP diet or probiotic cure runner’s gut?
There is not enough support to promise that. A 2025 review identifies low-FODMAP approaches, probiotics, hydrogel products, carbohydrate mixtures and gut training as active areas of study. Test any intervention cautiously and seek dietetic guidance before adopting a restrictive diet.
When should stomach symptoms be medically evaluated?
Seek professional help for persistent or severe symptoms, recurrent problems that disrupt training, dehydration, bleeding, fainting, fever or unexplained weight loss. Those signs require clinical assessment rather than further product experiments.
The practical takeaway
Fueling long runs without stomach problems is an experiment you conduct in training: choose a duration-appropriate carbohydrate target, pair it with a practiced fluid plan, use familiar formats, and adjust one variable at a time. The 2019 World Athletics range of 60–90 grams per hour for marathon running is a useful destination for athletes who can tolerate it, not a mandate. Consistency, access and personal tolerance determine the plan you can actually use.
Frequently Asked Questions
How much carbohydrate should I take on a marathon long run?
For 1–2.5-hour efforts, World Athletics lists 30–60 g/hour; for longer efforts, up to 90 g/hour. Marathon plans commonly use 60–90 g/hour, but start lower if you are not accustomed to fueling and build only as tolerated.
What is the least risky way to test a new gel or drink?
Use it on a noncritical long run, keep the meal and pace familiar, follow the label’s fluid directions, and change only that one variable. Repeat the combination before increasing the dose or switching products.
What should I do if I get nausea or diarrhea while running?
Record the dose, concentration, fluid, pace, weather and meal timing. Return to the last tolerated plan and change one factor at a time. Stop and seek medical advice for severe, persistent or alarming symptoms.
The Bottom Line
Use the 2019 World Athletics carbohydrate ranges as a starting framework, then rehearse the exact fuel, fluid, timing and carrying system you will use. A tolerable, practiced plan beats an aggressive target that your stomach cannot handle.
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