Stomach pain while running: causes and solutions

Nausea, stomach cramps, bloating, an urgent need to go at the 15-kilometer mark: digestive issues are one of the most frequent problems in endurance sports and one of the leading causes of DNF in ultra-distance events. Most have known causes and solutions that can be trained.

Why the stomach gives out during exercise

• Less blood for digestion. During exercise, blood is directed toward the muscles and skin. As intensity and heat rise, your digestive system receives less of it.
• The jostling. The repetitive impact of running churns the contents of the intestine, which explains why runners are more affected than cyclists.
• Dehydration. It slows down stomach emptying and worsens everything else.

The six most frequent causes

1. A drink that is too concentrated. Too much sugar in too little water: the drink stagnates in the stomach and draws water into it.
2. Too many carbohydrates of a single type. Beyond approximately 60g per hour, a single source of glucose saturates the intestine. The surplus ferments.
3. Fructose alone, in large quantities. It is absorbed better when accompanied by glucose.
4. Fiber, fat, and protein too close to the start. They slow down digestion.
5. An untrained intestine. Requiring 60g per hour during a race from a stomach that only trains with water is like running a marathon without doing any long runs.
6. Anti-inflammatories. Ibuprofen and medications in the same family irritate the digestive tract during exercise.

Pre-race stress and high doses of caffeine can also accelerate transit.

Solutions that work

• Train your gut. Consume your race carbohydrates during your long runs, gradually increasing the dose over several weeks. This is the most effective measure. The method is in How to train your body to consume more carbohydrates.
• Choose two types of carbohydrates. A glucose and fructose mixture in a ratio close to 2:1 uses two absorption pathways.
• Monitor the concentration. Almost everyone can tolerate up to 30g per 500ml. Beyond that, prefer carbohydrates that maintain low osmolality, such as highly branched cyclic dextrin (HBCD), and test them during training.
• Fractionate. Take small sips every 10 to 15 minutes rather than a large quantity every 45 minutes.
• Lighten up the 24 hours prior. Fewer fibers, fats, and spicy foods the day before; have your last meal 2 to 3 hours before the start.
• Stay hydrated with sodium in your drink during long efforts.
• Avoid anti-inflammatories before and during exercise.

If it happens mid-race

• Slow down or walk for a few minutes. Lowering the intensity brings blood back to the intestine.
• Switch to water in small sips for 10 to 15 minutes.
• Resume carbohydrates at half-dose as soon as it settles. Stopping nutrition completely leads to "hitting the wall."
• Cool yourself down if it’s hot: water on your head and the back of your neck.

Keep a short log

After each long run, note what you ate the day before and in the morning, what you consumed per hour, the weather, and your symptoms. After five or six runs, the causes will become obvious.

When to consult a doctor

Blood in the stool, intense pain, symptoms that persist after exercise, or symptoms that occur even at rest are not sports nutrition issues. Speak with a doctor.

The role of the formula

The ELIXYR Endurance Fuel was formulated around these principles: glucose and fructose in a 2:1 ratio, highly branched cyclic dextrin (HBCD) to keep osmolality low, and 340mg of sodium per serving. No formula replaces gut training, but starting with a drink designed for digestion eliminates one cause from the list. To understand the difference between carbohydrates, read HBCD or maltodextrin.