Dealing with Gastro-Intestinal Issues

by Asker Jeukendrup, Core Nutrition Planning

Gastro-intestinal (G.I.) complaints are very common for distance runners, with 30 to 50% reporting problems related to exercise.

The most common symptoms include: belching and vomiting, abdominal pain, gastroesophageal reflux (or heartburn), and bloating, abdominal pains and cramping, increased flatulence, urge to defecate, and loose stool, diarrhea or even bloody diarrhea.

While the specific causes of gastrointestinal symptoms are not completely understood, some laboratory studies have been performed, and the potential causes and contributors have been identified and categorized as: mechanical, physiological and nutritional.

The mechanical causes of GI-problems are related either to impact or posture. In running, repetitive high-impact mechanics are thought to be implicated in multiple issues: GI bleeding is common amongst runners and is thought to be symptomatic of damage to the intestinal walls due to repetitive impact. As well, repetitive bouncing is thought to contribute to symptoms such as flatulence, diarrhea and urgency.

Physiological causes of GI-symptoms include reduced blood flow and increased anxiety (especially before competition). During exercise, blood flow is preferentially redirected to the working muscles and blood flow to the gut can be reduced by as much as 80%. This can compromise gut function to varying degrees and can result in GI cramping. Anxiety has an effect on hormone secretion which in turn can affect gut movement, resulting in incomplete absorption and loose stool. 

A wide variety of nutrition factors can have strong influence on gastro-intestinal distress. Fiber, fat, protein, and fructose have all been associated with a greater risk to develop GI-symptoms. Dehydration, possibly as a result of inadequate fluid intake, may also exacerbate the symptoms. 

There are a number of steps you can take to prevent GI issues whether caused by mechanical, physical, or nutritional issues. Not all suggestions will work for everyone, but hopefully every sufferer can find one or two that do help address their specific issues. The guidelines below are based on limited research, but anecdotally these guidelines seem to be effective:

  • Avoid high fiber foods the day or even days before competition.
  • Avoid aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. 
  • Avoid milk products in the day or days leading up to a race as even mild lactose intolerance can cause problems during exercise.
  • Avoid fructose-only foods.
  • Avoid dehydration as it can exacerbate symptoms of any GI issues.

Practice new nutrition strategies so that you are comfortable executing the plan mechanically and ensure your body is trained to handle that level of intake.

Train your gut so that it can up-regulate to handle the levels of intake.

For more details and additional references, please see the full CORE Nutrition Planning article covering GI complaints, causes, and potential solutions.