What is GI Distress and How to Avoid It
You've trained your legs for months. Then ten miles in, it's your stomach that quits first: bloating, cramping, that sudden need to find a toilet. It's one of the most common and most frustrating problems in endurance sport and it has very little to do with fitness.
WHAT IS EXERCISE-INDUCED GI DISTRESS?
It's the general term for stomach and gut symptoms brought on by exercise: bloating, cramping, nausea, reflux, and the urgent need to go. Research suggests it affects up to half of endurance runners at some point and it's just as common amongst many runners and cyclists.
WHY DOES GI DISTRESS HAPPEN?
1. Blood gets diverted away from your gut
During hard or prolonged exercise, your body redirects blood toward working muscles, skin and lungs, away from your gut. At high intensity, blood flow to your gut can drop by as much as 80%. With less blood flow, your gut absorbs less effectively, empties more slowly and becomes more irritable, which is the main driver of exercise-related GI symptoms.
2. Too much carbohydrate too fast
Taking in a lot of carbohydrate, especially from a single sugar source, overwhelms your gut's capacity to absorb it. The unabsorbed carbohydrate draws in water and ferments, causing bloating, cramping and urgency. Always sip never gulp, a technique used by many professionals to help reduce risk of GI distress.
4. Mechanical jostling
Running in particular bounces your gut around far more than cycling or swimming, which is part of why runners report GI issues more often than other endurance athletes.
5. Heat, dehydration and nerves
Hot conditions and dehydration further reduce blood flow to the gut, and pre-race nerves slow digestion on their own, stacking the odds against you before you've even started.
HOW TO AVOID GI DISTRESS
To avoid GI distress, ensure to use blended carbohydrate sources. Combining glucose and fructose, rather than relying on one sugar, uses two separate absorption pathways in your gut, so you take in more carbohydrate with less left over to cause trouble. Fructose can however be harder to break down than glucose for many people, so if you’re someone who struggles with IBS or something similar, aim to have fuel with a 2:1 ratio or even 3:1.
Train your gut, practising your race fuelling in training, not just on race day, genuinely improves how well your gut absorbs and tolerates carbohydrates over time. Build up gradually rather than trying your full race nutrition on the first session. Start by taking gels or drink mixes on shorter, easier sessions, then build up as your mileage increases and sessions get longer so should the grams of carbohydrates you take. Your stomach is a muscle and must be trained just like your legs are.
Don't go in underfuelled or dehydrated. Starting a session dehydrated or carb-depleted makes your gut more sensitive, not less.
Practise under race conditions. Heat, pace and nerves all affect your gut, so test your fuelling plan in conditions that resemble the real thing, not just an easy Sunday run.
