Runner's Gut: Can You Train It? 2026 Research

The story out of a Hyrox race this week made every endurance athlete wince: a competitor pushed through a mid-race bout of diarrhea and still crossed the line first. It went viral for the obvious reason, but it points at something most runners already know from experience. The gut is often the first thing to quit during hard endurance work, long before the legs give out.

So can you actually do something about a rebellious stomach? A wave of 2026 sports-nutrition research says yes, at least partly, and the fix is more about practice than willpower.

Why your gut rebels during exercise

Hard endurance exercise pulls blood away from your digestive tract and sends it to your working muscles and skin. This drop in gut blood flow, combined with mechanical jostling and stress hormones, can loosen the intestinal barrier and slow digestion. Scientists call the whole cascade exercise-induced gastrointestinal syndrome, and it explains the cramping, bloating, and urgent bathroom stops that hit mid-effort.

Key Takeaway: Runner's gut is not a willpower problem. It is a physiological response to reduced blood flow, physical jostling, and stress hormones during hard, prolonged exercise.

How common is runner's gut?

GI symptoms during endurance exercise are the norm, not the exception. A 2026 review in Sports Medicine reports that up to 80% of ultra-endurance runners experience symptoms such as nausea, bloating, abdominal pain, and the urge to defecate. The longer and harder the event, the more likely the gut protests.

Stat: Up to 80% of ultra-endurance runners report gastrointestinal symptoms during events, according to a 2026 review in Sports Medicine.

Can you train your gut?

Yes, and this is the part that surprises people. The gut adapts to what you repeatedly ask of it, much like muscles adapt to training. A 2023 systematic review in Sports Medicine found that two weeks of repeated carbohydrate feeding during exercise cut gut discomfort by about 47% and reduced carbohydrate malabsorption by 45 to 54%. In practice, that means deliberately eating and drinking during your longer sessions instead of saving fuel for race day.

Key Takeaway: "Gut training" is real. Practicing your race-day fueling during training sessions can meaningfully reduce mid-effort GI distress over a few weeks.

If you have ever tried a gel for the first time during a race and regretted it, this is why. Race day is the worst possible moment to introduce your stomach to something new. The same logic applies to everyday eating: sudden changes rarely go smoothly, whether you are ramping up fiber quickly or overhauling your diet overnight.

How much fuel can the gut actually handle?

Current guidelines suggest up to about 90 grams of carbohydrate per hour for prolonged, intense endurance events, but most people cannot tolerate that without practice. For loading in the days beforehand, a 2026 dose-response study in the Scandinavian Journal of Medicine and Science in Sports found that 10 grams of carbohydrate per kilogram of body weight per day produced the highest muscle glycogen stores, with no jump in GI symptoms other than a feeling of fullness.

Stat: Endurance fueling guidelines reach up to 90 g of carbohydrate per hour during long events, but tolerance for that intake has to be built gradually.

The low-FODMAP strategy, used carefully

Some athletes cut high-FODMAP foods (certain fermentable carbs found in onions, wheat, beans, and some fruits) to calm a sensitive gut. A 2026 Current Opinion paper in Sports Medicine argues this works best as a short-term tactic around key sessions or competition rather than a permanent diet. For milder cases, a more relaxed approach usually makes more sense, since long-term restriction can crowd out nutrients you actually need. Notably, the same research found FODMAP tweaks did not reliably improve performance, only comfort. If reflux is your main issue rather than lower-gut symptoms, the triggers behind acid reflux follow a different playbook.

What about hydrogels and probiotics?

The fancier options are less of a shortcut than the marketing suggests. Several 2026 reviews found that carbohydrate hydrogels, the gels designed to pass through the stomach more smoothly, do not consistently beat standard carbohydrate products for symptoms or performance. Probiotics show mixed results, though one 2026 trial in trail runners found a specific strain (Lactiplantibacillus plantarum 299v) was linked to less gut inflammation after racing. Promising, but not a guarantee.

A simple plan if you are not an elite

You do not need a lab to apply any of this. Start fueling during your longer training sessions rather than toughing them out dry. Rehearse your exact race-day food and drink weeks ahead. Build carbohydrate intake gradually instead of all at once. And do not forget fluids and sodium, since dehydration makes GI symptoms worse, especially in heat, which is why electrolyte needs climb in hot conditions.

Key Takeaway: Treat your gut like any other trainable system. Practice fueling in training, build intake slowly, and never debut a new food or gel on race day.

The athlete who finished that Hyrox race despite everything got the headlines. The quieter lesson is that most of us can avoid the situation entirely with a few weeks of practice. Your stomach learns. You just have to teach it.

-- Selena

Sources

FAQ

What is runner's gut?

Runner's gut is the common name for gastrointestinal symptoms during endurance exercise, such as cramping, bloating, nausea, and an urgent need to use the bathroom. It stems from reduced blood flow to the digestive tract, physical jostling, and stress hormones during hard, prolonged effort.

Can you really train your gut to handle more food?

Yes. Research suggests the gut adapts to repeated fueling. A 2023 systematic review found that two weeks of regular carbohydrate intake during exercise reduced gut discomfort by around 47% and improved carbohydrate absorption, so practicing your fueling in training can pay off on race day.

How much carbohydrate should I eat during a long event?

Guidelines suggest up to about 90 grams of carbohydrate per hour for prolonged, intense endurance events. Most people cannot tolerate that without gradual practice, so build your intake slowly over several weeks of training rather than attempting the maximum on race day.

Does a low-FODMAP diet help with exercise GI symptoms?

It can, but mainly as a short-term tactic. A 2026 review found low-FODMAP eating around key sessions may ease symptoms for athletes with severe distress, though it did not reliably improve performance. Long-term restriction is usually unnecessary and can limit important nutrients.

Why do GI problems get worse in the heat?

Heat and dehydration reduce blood flow to the gut even further and concentrate the digestive stress of exercise. Staying on top of fluids and sodium helps, which is why electrolyte and hydration planning matters more in hot conditions.