Amy Stephens


Licensed dietitian

specializing in sports nutrition

and eating disorders

How to prevent gi issues in runners

We all know far too well that gastrointestinal issues can derail a training run or race physically and mentally. Cramping, bloating, and diarrhea can quickly worsen dehydration and become very painful or even debilitating. In this post, I outline some easy strategies to help you feel better and improve performance when facing GI issues. By following these nutrition strategies, one can improve symptoms and performance as a whole.

GI issues can happen before, during, or after a run and can rapidly cause dehydration and electrolyte imbalance. If GI issues are not addressed, they can lead to underfueling, cramping, and poor performance. Underfueling will eventually lead to hitting the wall, or even dropping out of a race altogether.

Why do GI issues happen with some athletes?

There are a few reasons for GI issues in runners. 

  1. As you run, the stomach and gut are literally being shaken, and this makes it difficult for your body to digest foods. 
  2. Running also requires the body to divert blood flow away from the gut to supply oxygen rich blood to the working muscles. This process makes it very difficult for the body to digest food and run at the same time.
  3. Feeling nervous can also cause GI issues. Nervousness is something I’ve experienced myself during track workouts! Typically, if I dive a bit further into how an athlete feels before a race or track workout, feelings of nervousness usually surface. Breathing and mental exercises can help soothe an athlete’s nerves. Similar to running, feeling nervous takes blood supply away from the gut and diverts it to the nervous system to cope with stress (elevated heart rate, sweat, increased blood supply to brain, etc.).

Nutrition strategies to prevent GI issues:

It’s important for athletes to ensure they’re hydrated before heading out for a run. When exercising, the blood is shunted to working muscles and away from the gut causing a lower blood volume. Ultimately, any food or sports beverage you consume during a workout may cause GI distress. 

Time meals so you finish eating at least one hour before running. Work with a sports dietitian to time your food so it’s digested by the time you start exercising. 

Hydrate by drinking 10-20 oz of water one hour before a run and 2-4 oz every 15 min for runs lasting one hour or longer. You might need to do a sweat test to see how much water your body loses. Take note that you lose more water when exercising in hot, humid, dry, and high altitude. 

Foods – Include bland foods such as, rice, bananas, oatmeal, dry toast, or potatoes before your run. Another dietary strategy is called Low Fodmap which has been shown to help with GI symptoms. I’ll write more about this and how to follow in a separate post.

Quick tips: 

  • Eat at least one hour before running 
  • 10-20 oz of water before, then 2-4 oz every 15 min (depending on heat, humidity, altitude) 
  • Limit caffeine or switch to tea
  • Limit spicy foods, high-fat foods, high-fiber foods (beans or lentils) or dairy. 

Try these gu’s, gels, and chews during your run because they are made with fewer processed ingredients. Instead of maltodextrin, they use monosaccharides like glucose and fructose which are easier for the body to digest. They are best tolerated with a gulp of water.

Try these Gels, Gu’s or chews


Honey stinger website 

Untapped energy gels website 

Huma energy gels – website


Energy chews are great because you can ingest them at a slower rate. This allows your gut to work more slowly and not cause GI issues. For best results, you may take a few at a time. 

Liquid sports drinks such as Skratch or Maurten can be helpful because they are hydrating and can be taken in a small amount at a time. When using, be careful not to overwhelm the gut by ingesting too much too fast. 

You can also ask your doctor about the over the counter medication called imodium.


Gibson PR, et al. Other dietary confounders: FODMAPS. Dig Dis. 2015;33(2):269–276.

Lis DM. Exit Gluten-Free and Enter Low FODMAPs: A Novel Dietary Strategy to Reduce Gastrointestinal Symptoms in Athletes. Sports Med. 2019 Feb;49(Suppl 1):87-97. 

O’Keeffe M, Lomer MC. Who should deliver the low FODMAP diet and what educational methods are optimal: a review. J Gastroenterol Hepatol. 2017;32(Suppl 1):23–26. 

Staudacher HM, et al. Comparison of symptom response following advice for a diet low in fermentable carbohydrates (FODMAPs) versus standard dietary advice in patients with irritable bowel syndrome. J Hum Nutr Diet. 2011 Oct;24(5):487-95.

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