Gut Training for Marathons: How to Train Your Stomach to Take 90g of Carbohydrate Per Hour

The Problem: You Know the Target But Cannot Hit It

A common marathon pattern: the runner hears they should take more carbohydrate during long races. They try a bigger gel schedule once. Their stomach rebels. They conclude they cannot handle gels. They go back to under-fueling and fade late.

The conclusion may be wrong. The problem is often not permanent gel intolerance. It is lack of progression.

The gut, like the legs, adapts to repeated training. If you only take one gel on occasional long runs, then suddenly ask your gut to process 60 or 90 grams of carbohydrate per hour at marathon effort, you have not built the skill. You have staged an ambush.

What Gut Training Actually Is

Gut training is the deliberate practice of consuming carbohydrate during running so your gastrointestinal system becomes better at tolerating and absorbing race-day fuel.

It is not random gel experiments, running fasted to teach fat burning, or ignoring GI distress while hoping for heroism.

It is:

• Practicing carbohydrate intake during runs
• Starting with what you can tolerate now
• Increasing intake gradually
• Using the same products you plan to race with
• Practicing timing, water intake and pre-run meals
• Learning which symptoms improve with practice and which require another solution

Think of gut training as progressive overload for your stomach. You would not jump from a 10-mile long run to a 22-mile long run without progression. Do not jump from 30g/hour to 90g/hour and blame the gel when your stomach stages a protest.

Why the Gut Is Trainable

The gut is not a passive tube. It adapts to what you ask it to do. In endurance sports, carbohydrate has to move from your mouth to your stomach, from your stomach to your small intestine, across the intestinal wall, and into circulation while blood flow is also being demanded by working muscles.

Carbohydrate transporters matter

Glucose and fructose use different transport pathways in the small intestine. Because these pathways differ, combining carbohydrate types can increase total carbohydrate absorption compared with relying on glucose alone. This is the reason modern high-carbohydrate sports products often use combinations such as maltodextrin plus fructose or glucose plus fructose. For events longer than about 2.5 hours, sports nutrition guidance commonly supports up to about 90g/hour from multiple transportable carbohydrates.

Repeated exposure helps

Practicing carbohydrate and fluid intake in training can improve stomach comfort, tolerance and race-day execution. The goal is to expose the gut to the same conditions it will face in competition: running intensity, product type, carbohydrate amount, fluid volume and timing.

Why water matters

Many gels are concentrated. Taking them without water can increase GI discomfort. Water helps dilute the carbohydrate load and supports movement from the stomach into the intestine.

Who Needs Gut Training and Who Does Not

Not every marathon runner needs 90g/hour. But almost every marathon runner benefits from practicing their fueling plan.

You probably need gut training if:

• You currently take fewer than 40g/hour during long runs
• You fade late despite decent training
• You get nausea, bloating, cramping or urgency during long runs
• You plan to race for more than 2.5-3 hours
• You want to increase carbohydrate intake beyond your current level
• You have never practiced your exact race-day fueling plan

The safest assumption: practice. Even if you do not need a full 90g/hour progression, you should know exactly what your stomach does with race-day fuel before race day arrives.

The Progressive Overload Protocol

This protocol builds from 30g/hour toward 90g/hour across a 12-16 week marathon block. Adjust the starting point based on what you already tolerate.

Phase 1: Baseline, weeks 1-3

Target: 30-45g carbohydrate per hour on runs longer than 60-75 minutes. The goal is consistency. Fuel the medium-long run and the long run. If you already tolerate 45g/hour easily, start there.

Phase 2: Build, weeks 4-8

Target: 45-70g carbohydrate per hour. Increase by about 10-15g/hour every 1-2 weeks. Hold steady if symptoms appear.

Phase 3: Race-specific build, weeks 9-13

Target: 70-90g/hour if needed and tolerated. This is where you practice the actual race-day plan. Use the same gel brand, same drink mix, same flavors, same caffeine strategy and same timing. Include at least one long run where you practice your full intake at or near marathon effort.

Phase 4: Taper, weeks 14-16

Do not introduce new products. Keep practicing the timing on runs longer than 60 minutes, but reduce the total fueling because the runs are shorter. Nothing new. Nothing heroic in the final week.

What if symptoms appear?

• Mild bloating: Hold the same intake for another week.
• Nausea: Add more water, slow the rate of intake, or try a different product format.
• Cramping: Check concentration, hydration and product ingredients.
• Urgency or diarrhea: Reduce intake, review pre-run fiber/fat/caffeine, and consider medical input if recurring.

What to Eat Before Training Runs

Gut training is not only about what you take during the run. The pre-run meal can either support the session or sabotage it.

Before gut-training long runs

• Eat 2-3 hours before the run when possible
• Choose high-carbohydrate, low-fat, lower-fiber foods
• Use familiar foods
• Avoid large portions of fat, beans, raw vegetables or unfamiliar dairy
• Practice the same timing you plan to use on race morning

Good pre-run options

• Bagel with jam or honey
• Toast and banana
• Oatmeal if tolerated
• White rice with a small amount of soy sauce
• Rice cakes with honey

Caffeine

If you plan to use coffee or caffeinated gels on race day, train with them. Caffeine can affect gut motility and urgency in some runners. Race day is not the time to discover that your performance boost has an unexpected side quest.

What to Take During Training Runs

The basic rule: fuel by schedule, not by hunger. Hunger and low-energy feelings often arrive late. By the time you feel like you need fuel, you may already be behind.

Timing protocol

• First gel or carb dose around 30-45 minutes
• Repeat every 20-30 minutes depending on target intake
• Take gels with water when possible
• Count carbohydrate from sports drink toward the hourly total
• Practice opening packets, carrying fuel and drinking while running

Example schedules

Gels, Drinks, Chews and Products

The product type matters less than practicing with the exact product you will race with. That said, some features are worth understanding.

Standard gels

Most standard gels contain about 20-25g carbohydrate per packet. They work well for runners building up to 60g/hour. At higher targets, the gel frequency gets high.

High-carbohydrate gels

Higher-carbohydrate gels often contain 30-40g per packet, often using multiple carbohydrate sources. They are increasingly popular for runners targeting 80-90g/hour because they reduce the number of packets needed.

Drink mixes and sports drinks

Carbohydrate drink mix can add substantial hourly carbohydrate without adding more packets to manage. The trade-off is that you are more dependent on course aid-station drinks or carrying fluid.

Chews and real food

Some runners prefer chews, dates, rice balls or other real food, especially on longer courses. If you plan to use real food on race day, practice it in training. Your stomach does not intuit your preferences from the sidelines.

Caffeine

Caffeinated gels used strategically in the second half of a marathon can support performance. Practice the dose, timing and brand in training before deploying them on race day.

The brand consistency rule

Use the same brand, flavor and format in training that you will use on race day. Switching brands the night before a marathon and discovering an unexpected GI response is one of the sport's more memorable unnecessary experiences.

Common GI Problems and What Gut Training Can Fix

Nausea

Common causes: concentrated gel without enough water, too much intake too fast, high-fat pre-run meal, heat, anxiety, dehydration.

What helps: always take gel with water; slow the intake rate; address pre-run meal; practice at race effort.

Bloating and sloshing

Common causes: too much fluid, too much concentrated carbohydrate, high-fiber pre-run food, or swallowing air.

What helps: smaller, more frequent gel doses; adjust pre-run meal; reduce single-dose concentration.

Stomach cramps

Common causes: high-fructose products in excess, dehydration, pre-run diet, intensity, under-practiced products.

What helps: reduce fructose-heavy products; hydrate consistently; practice at race pace.

Urgency and bathroom issues

Common causes: pre-run high-fiber/fat/dairy foods, caffeinated gels, new products, anxiety, or simply normal gut motility at pace.

What helps: clean pre-run diet; practice caffeine dose; reduce high-fructose intake if contributing.

What gut training cannot fix

Some GI issues are medical in origin: irritable bowel syndrome, celiac disease, inflammatory bowel disease, or other conditions that affect gut function. Gut training can improve tolerance to race-day fueling, but it is not a substitute for a medical workup if symptoms are severe, persistent or outside the norm.

Race-Day Execution

Race day is practice day with higher stakes. The plan should be settled long before the start.

The race-day fueling checklist

• Same pre-race meal you practiced in long runs
• Same timing before the gun
• Same gels or products, same brand, same flavors
• Know your fueling schedule before the race starts
• Take the first gel around 30-40 minutes, not when you feel hungry
• Take gels with water, not sports drink, unless you have practiced the combination
• Keep taking fuel through the second half even when the stomach is protesting mildly
• Know which aid stations have water versus sports drink

The number one race-day mistake

Waiting too long to start fueling, then taking too much too fast in the second half when the stomach is less tolerant of concentrated carbohydrate under fatigue and heat.

Early fueling. Consistent fueling. Same products you practiced with. That is the whole thing.

Use the marathon fueling calculator to build your race-day plan →

Marathon Gut Training FAQ

What is gut training for marathon runners?

Gut training is practicing carbohydrate intake during training runs so the digestive system becomes better at tolerating and absorbing fuel at race effort. It works by progressively increasing intake over weeks to build tolerance.

How many grams of carbohydrate per hour do I need?

Many runners do well with 40-70g/hour. Trained runners targeting faster times or racing for more than 2.5 hours may benefit from building toward 70-90g/hour using multiple carbohydrate sources.

Can I train my gut to handle more gels?

Yes. The gut is trainable. Consistent practice at increasing intake levels typically improves comfort and tolerance over several weeks.

How do I start gut training if I get nausea from gels?

Start lower than your current tolerance limit. Take gels with water. Use a familiar product. Practice on medium-long runs before long runs. Increase intake by small amounts every 1-2 weeks.

Should I use the same products in training and on race day?

Absolutely. Whatever you race with should be practiced extensively in training. Do not try new flavors, brands or caffeine doses for the first time on race day.

What should I eat before a long gut-training run?

High-carbohydrate, lower-fat, lower-fiber food 2-3 hours before the run. Bagel, toast, banana, oatmeal, rice cakes. Avoid large portions of fat, dairy, beans or raw vegetables.

Why do I feel nauseous during marathon pace running?

Common causes include concentrated gel without enough water, too-high intake rate, heavy pre-run meal, heat, dehydration or anxiety. Practice gel timing, always take with water, and address the pre-run meal.

Should I fuel during every long run?

Yes, if the run is longer than about 60-75 minutes. Gut training only works if you practice. Fueling inconsistently across the block leaves the stomach unprepared for race day.

Does gut training work for every runner?

Most runners can improve tolerance through consistent practice. Some GI issues are medical in origin and may not improve with training alone. Severe or persistent GI problems should be discussed with a clinician.

What is the best gel for marathon gut training?

The best gel is the one you will actually use on race day, practiced consistently in training. Flavor, texture, caffeine dose and brand should all be familiar before race morning.

Generate a personalized marathon training plan with fueling guidance →