Fueling Without GI Issues: How to Eat and Run Without Stomach Problems

You've read the articles. You know you should be taking 60g of carbs per hour on long runs. But every time you try, your stomach cramps, you feel nauseous, or you're sprinting to the bathroom.

So you dial it back. You take fewer gels, eat less before your run, and hope for the best. Your stomach feels better — but your energy crashes.

It's not a choice between fueling well and feeling good. You can do both. Here's how.

During exercise, your body redirects blood away from your digestive system and toward your working muscles. Blood flow to your gut can drop by 50–80% during hard running. That means your stomach is trying to process food with a fraction of its normal capacity.

At the same time, the physical bouncing of running agitates your stomach and intestines. Add in the concentrated sugar solution from gels and sports drinks, and you have a recipe for nausea, cramping, bloating, and worse.

Follow these five steps to increase your fueling without increasing your bathroom visits.

Your gut is adaptable. The transport proteins that absorb carbohydrates increase in number when you practice fueling during exercise. Research shows that gut training over 4–6 weeks can double your carb absorption capacity.

Do not jump straight to 60g/hour. Build up over a few weeks just like you build mileage.

Not all fueling products are created equal when it comes to GI comfort. Some are much more likely to cause problems than others.

Fructose is the #1 GI trigger in runners. It's absorbed slowly and through a different pathway than glucose. If a gel or drink has more than 15g of fructose per serving and your gut isn't trained for it, you're rolling the dice.

• Full meal: 2–3 hours before your run. Never closer.
• Light snack: 60–90 minutes before, carbs only, under 30g.
• Quick top-up: 15–20 minutes before, simple carbs only (gel, banana).
• During run: start at 20–30 minutes in, not when you feel hungry.

The most common timing mistake is eating a full meal 45–60 minutes before running. Your stomach hasn't emptied yet, the food is sitting there, and the bouncing plus reduced blood flow is a GI disaster.

In the 4–6 hours before a run, avoid or limit these:

• High-fiber foods (whole grains, raw vegetables, beans, bran)
• High-fat meals (fried food, heavy cheese, fatty meats)
• Excess fructose (fruit juice, agave, honey in large amounts)
• Spicy foods (especially if you're prone to heartburn)
• Large doses of caffeine if you're not habituated (more than your normal coffee)
• Sugar alcohols (found in many "sugar-free" protein bars)

Hydration directly affects GI comfort. Too concentrated a carb solution (like taking a gel with no water) pulls fluid into your gut and causes cramping. Too diluted, and you're not getting enough fuel. The sweet spot is a 6–8% carbohydrate solution — which is what most standard sports drinks provide.

• Always take gels with 150–250ml of water — never dry.
• Use an electrolyte drink with sodium (300–600mg per 500ml) to support fluid absorption.
• Dehydration worsens GI symptoms — don't under-drink either.

• Full meal 2–3 hours before (carbs + moderate protein, low fat/fiber)
• Light top-up 15–20 min before (simple carbs only)
• First fuel at 20–30 minutes into the run
• Maltodextrin or glucose-based products (not high-fructose)
• Every gel taken with 150–250ml water
• Electrolyte drink with sodium throughout
• No new products on race day — only what you trained with
• Build carb intake gradually over 4–6 weeks (gut training)

MAVR starts with your current fueling tolerance and builds from there.

• Starts conservative with carb targets based on your experience level
• Increases fueling recommendations gradually as you log tolerance
• Recommends low-GI-risk products based on your preferences
• Times every meal and fuel intake to minimize stomach issues