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Prevention of gastro-intestinal problems in athletes

This is the third of a series of 3 posts on gastro-intestinal problems.

Unfortunately, GI-problems are very common, especially amongst endurance athletes and they can easily ruin a race (Read here). The symptoms are diverse and so are the causes (Read here). However, there appear to be a number of ways to reduce the risk. Not all of these suggestions may work for everyone, but hopefully every sufferer can find one or two ways out of this list that will work for them. The guidelines below are based on limited research, but anecdotally these guidelines seem to be effective:

Avoid high fiber foods

Avoid high fiber foods in the day or even days before competition. For the athlete in training, a diet with adequate fiber will help to keep the bowel regular. Fiber before race day is different. By definition, fiber is not digestible, so any fiber that is eaten essentially passes through the intestinal tract. Increased bowel movements during exercise are not desirable and will accelerate fluid loss. It may also result in unnecessary gas production which might cause cramping. Especially for those individuals who are prone to develop GI-symptoms a low fiber diet the day before (or even a couple of days before) is recommended. Choose processed white foods, like regular pasta, white rice, and plain bagels instead of whole grain bread, high fiber cereals, oats and brown rice. Check the food labels for fiber content. Most fruits and vegetables are high in fiber but there are a few exceptions: zucchini, tomatoes, olives, grapes, and grapefruit all have less than one gram of fiber per serving.

Increased bowel movements during exercise are not desirable and will accelerate fluid loss. It may also result in unnecessary gas production which might cause cramping.

Avoid aspirin and non-steroidal anti-inflammatory drugs (NSAIDs)

Avoid aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Both aspirin and NSAIDs are commonly have been shown to increase intestinal permeability and may increase the incidence of GI complaints. The use of NSAIDs in the pre-race period should be discouraged.

Avoid milk products

Avoid milk products that contain lactose as even mild lactose intolerance can cause problems during exercise. For instance, it is possible to avoid milk completely or get lactose free milk. Soy, rice, and almond milks generally don't contain lactose.

Avoid fructose-only foods

Avoid high fructose foods (in particular drinks that have exclusively fructose). Fructose is not only found in fruit, but also in most processed sweets; candy, cookies etc., in the form of high fructose corn syrup. Some fruit juices are almost exclusively fructose. Fructose is absorbed by the intestines more slowly the tolerance of fructose is much less than glucose (may lead to cramping, loose stool and diarrhea). Having said that, I have discussed before that fructose in combination with glucose may not cause problems and may even be better tolerated (see the full blog here).

Avoid dehydration

Since dehydration can exacerbate GI-symptoms it is important to avoid dehydration. Start the race well hydrated.

Practice new nutrition strategies

Make sure to experiment with your pre-race and race-day nutrition plan many times prior to race day. This will allow you to figure out what does and does not work for you, and to reduce the chances that GI issues will ruin your race.

Train your gut

Training the gut is another practice. If your gut is adapted to the foods you consume during a race, you are less likely to get stomach problems. If you are avoiding carbohydrate in daily life, your intestines will respond by reducing intestinal transporter numbers so your ability to absorb carbohydrate is reduced. On race day you may not be able to absorb all of the ingested and this may cause GI-issues. The advice is therefore not to restrict carbohydrate intake and regularly consume carbohydrate during training. Read more about training your gut here.


  1. de Oliveira, E. P., Burini, R. C., Jeukendrup, A. 2014. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med 44 Suppl 1: S79-85.

This full reference can be downloaded FREE here.


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