You are close to your marathon, but your long runs have not included enough carbohydrate. That is fixable—but race day is not the place to suddenly force down multiple gels. Learning how to train your gut for marathon fueling means practicing the same carbohydrate amount, product type, fluid, and timing you plan to use in the race, then increasing one variable at a time.
The goal is not to eat as much as possible. It is to find the highest carb intake you can absorb comfortably while still running well.
Quick Answer
Start with 30-40 grams of carbohydrate per hour on your next long run if you have been taking in very little. Hold that level for one or two runs, then increase by 10-15 grams per hour if your stomach stays settled.
Most first-time marathoners do well targeting 45-60 g of carbohydrate per hour by race day. Runners expecting to be on course longer, running at a hard effort, or using mixed carbohydrate products may eventually tolerate 60-75 g per hour, but only if they have practiced it.
Use a simple routine: take a small serving every 20-30 minutes, drink to thirst with extra water when using concentrated gels, and avoid changing both your fuel product and carb target in the same session.
Why This Happens
During a marathon, your muscles rely heavily on stored glycogen and blood glucose. Glycogen stores are limited, especially once you run beyond roughly 90 minutes. Carbohydrate taken during the race helps preserve available energy and can reduce the late-race slowdown that happens when effort starts to feel much harder than expected.
The problem is that exercise reduces blood flow to the digestive system. Running impact, heat, dehydration, pre-race nerves, and taking a large bolus of sweet fuel can all make the gut feel worse. If you normally run on water alone, suddenly taking 60-90 g per hour can cause sloshing, cramps, nausea, urgency, or diarrhea.
Gut training works because repeated exposure helps you learn practical tolerance. You identify a product texture you can handle, establish a feeding rhythm, and discover how much water you need with that product. Your body may also become better at moving and using carbohydrate during exercise, but the immediate benefit is often simpler: fewer surprises.
Step-by-Step Method
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Choose one starting format. Use gels, chews, sports drink, or a combination. Check the label rather than guessing: many gels provide 20-30 g of carbohydrate, while sports drink can range widely by bottle or flask. Choose products available on your marathon course when possible.
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Begin below your race target. If you currently take little or no fuel, start at 30-40 g per hour. For example, take one 25 g gel around 25-30 minutes and another around 55-60 minutes. On a two-hour run, that is enough practice without overwhelming your stomach.
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Split intake into small, regular doses. Do not wait until you feel depleted. A useful default is 20-25 g every 25-30 minutes, starting within the first 30 minutes. Small, scheduled doses are usually easier to tolerate than two gels taken close together late in the run.
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Match gels with fluid. Most standard gels are concentrated and usually work best with water. Take a few mouthfuls of water after a gel, following the brand instructions where provided. If you use sports drink for most of your carbs, avoid automatically adding several gels on top; total carbohydrate per hour is what matters.
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Increase gradually across long runs. Add only 10-15 g per hour after a comfortable session. Keep the same product, route intensity, and approximate weather conditions when testing a higher amount. That makes it easier to identify what caused a problem.
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Practice at marathon-like effort. Easy long runs are useful, but fueling can feel different at marathon pace because intensity changes digestion. Include your race fueling routine during long runs with marathon-pace segments or during a steady progression run.
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Rehearse the full race plan once or twice. In the final major long runs, practice your planned breakfast, start timing, fuel schedule, bottle or aid-station strategy, and any caffeine product. Do not use the final week to chase a new carb record.
A practical week-by-week progression
If you have four or more long runs remaining, use this progression. If you have only two or three, prioritize consistency at a moderate amount instead of making aggressive jumps.
- Four weeks out: 30-40 g/hour on the long run. Test one gel type plus water, or a measured sports drink.
- Three weeks out: 40-50 g/hour. Keep the same schedule and add one small serving.
- Two weeks out: 50-60 g/hour during your final substantial long run, including marathon-pace work if it is already in your plan.
- Race week: Keep food familiar. Use your established race target, typically 45-60 g/hour for a first marathon, rather than experimenting with a higher amount.
If your plan has six or more weeks left, repeat each level for two long runs before moving upward. More time allows a calmer, more reliable progression.
Common Mistakes
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Saving the first gel until mile 10 or until energy crashes. By then, you are trying to correct a deficit. Instead, begin fueling early and follow the clock: the first serving around 25-30 minutes is a practical starting point.
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Taking gels without enough water. A gel can sit heavily when chased with only a tiny sip, especially in warm weather. Instead, plan water access around each gel or choose a drink-based strategy that supplies both fluid and carbohydrate.
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Increasing carbs, caffeine, and fiber changes all at once. This makes GI problems impossible to diagnose. Instead, change one variable per long run. Test caffeine separately from your basic fuel plan.
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Copying an elite runner’s 90 g/hour plan. Higher intake can work, but it is not automatically better for every runner. Instead, build toward the lowest amount that reliably supports your pace and leaves your stomach calm.
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Using only a total-race number. Saying “I need six gels” does not tell you when to take them. Instead, write a time-based schedule and set watch alerts if needed.
Checklist or Decision Table
| Situation | Carb target | Practical approach | Key caution |
|---|---|---|---|
| No fueling practice yet | 30-40 g/hour | One 20-25 g gel every 30-40 minutes with water | Do not jump straight to race-course maximums |
| Comfortable with one gel/hour | 40-50 g/hour | Gel every 30 minutes, or drink plus one gel | Count carbs from every source |
| Preparing for a first marathon | 45-60 g/hour | 20-30 g every 25-30 minutes | Practice at least twice before race day |
| Using sports drink at aid stations | Varies by drink | Calculate grams per cup or bottle, then fill gaps with gels | Cup volume and mixing strength vary |
| Hot race or heavy sweating | Same carb target, fluid adjusted | Drink to thirst and use planned aid stations | More water does not mean more gels |
| Nausea or urgent bowel symptoms | Reduce to last comfortable level | Slow intake, use water, simplify products | Persistent symptoms need professional advice |
Before each key run, confirm: product packed, grams per serving known, first intake time set, water source identified, and post-run notes planned. Record what you took, when, weather, pace, fluid, and symptoms. That small log quickly reveals patterns.
When This Advice Does Not Apply
This general plan is not a substitute for individual medical or sports-nutrition guidance. Seek advice from a qualified clinician or sports dietitian if you have diabetes, a diagnosed gastrointestinal condition, a history of eating difficulties, repeated fainting, or medication that affects blood sugar or hydration.
Do not push through severe abdominal pain, repeated vomiting, confusion, inability to keep fluids down, or symptoms of heat illness. Stop exercise and get appropriate help. Also, if a product consistently causes symptoms even at a low dose with water, switch products rather than trying to “toughen up” through distress.
Very short runs do not need marathon-level fueling practice. Use runs longer than about 75-90 minutes, or workouts that include sustained race-pace work, for meaningful testing.
Realistic Example
A first-time marathoner has three long runs left and normally drinks only water. Their goal pace suggests a finish near four and a half hours. On the first long run, they take two 25 g gels over two hours, each with water: 25 g/hour. They feel fine but notice they waited too long for the first gel.
The next week, they start at 25 minutes and take a 25 g gel every 30 minutes for a total near 50 g/hour. They use the same flavor, carry water for the first hour, and take water at planned stops afterward. Their stomach stays comfortable during easy running and a 30-minute marathon-pace segment.
For the final substantial long run, they repeat 50-55 g/hour, test the race breakfast, and use one caffeinated gel late in the run. Because that goes well, they do not increase further. Their race plan becomes simple: start fueling at 25 minutes, take one gel every 30 minutes, drink water with gels, and use sports drink only if it replaces—not adds to—the planned carbohydrate amount.
Final Takeaway
The best marathon fueling plan is the one you have practiced at race-like effort without GI trouble. Start lower than your goal, use small doses on a schedule, and increase by only 10-15 g per hour after comfortable long runs.
For most first-time marathoners, 45-60 g of carbohydrate per hour is a sensible race-day destination. Consistency beats an ambitious number that your stomach has never handled.
FAQs
How many grams of carbs per hour should a first-time marathoner take?
Most first-time marathoners should aim for 45-60 grams of carbohydrate per hour once they have practiced that intake. If you have not fueled long runs before, begin around 30-40 g/hour and build up gradually. Your finishing time, pace, heat conditions, and product tolerance all matter, so there is no single mandatory number. A runner who comfortably absorbs 50 g/hour on schedule will usually do better than one who attempts 75 g/hour and develops nausea or misses later fuel.
How do I train my gut for gels when I usually run without food?
Start by taking one familiar gel with water during an easy run lasting at least 75-90 minutes. Use it early, around 25-30 minutes, rather than waiting for fatigue. On the next long run, repeat the same product and timing before adding another serving. Increase total intake by roughly 10-15 g/hour only after a symptom-free run. Testing on easy runs first reduces variables, while later marathon-pace segments show whether the routine works under more realistic stress.
Should I use gels or sports drink for marathon fueling?
Either gels or sports drink can work, and a combination is often practical if you calculate the total carbohydrate correctly. Gels make intake predictable and portable, but usually require planned water. Sports drink supplies fluid and carbohydrate together, but aid-station cup sizes and drink concentration may be inconsistent. Choose the option that you can carry, tolerate, and access reliably. If the race serves a drink you dislike or have not tested, carry your own fuel instead of relying on it.
Do I need water with every energy gel during a marathon?
Usually, yes, standard energy gels are best taken with some water unless the product label specifically says otherwise. Water helps dilute the concentrated carbohydrate in the stomach and may reduce the heavy, overly sweet feeling some runners get. You do not necessarily need a full bottle for each gel; several comfortable mouthfuls at an aid station may be enough. Avoid taking a gel immediately before a large amount of strong sports drink unless that combination was practiced in training.
What should I do if gels make me nauseous on long runs?
First, reduce the dose and simplify the setup rather than abandoning fueling altogether. Take smaller servings more frequently, slow your pace briefly while taking them, and use water with each gel. Check whether you are taking gels too late, combining them with too much sports drink, or using a flavor that feels overly sweet. Also consider heat, dehydration, high pre-run fiber, and caffeine as possible contributors. If nausea repeatedly occurs even with low intake, seek individualized advice from a sports dietitian or clinician.
Can I increase marathon carb intake in the final two weeks before race day?
Yes, but keep the increase modest and only use it on planned training sessions where you can observe the result. If you have never fueled, moving from zero to a practiced 40-50 g/hour is more useful than trying to reach an aggressive target immediately. Your final substantial long run is the best rehearsal opportunity. During race week, prioritize familiar foods and products, and do not introduce new gels, drink mixes, high caffeine doses, or a much larger carbohydrate load at the expo or start line.