Low-FODMAP diet for better management of gastrointestinal issues during exercise

Among running colleagues, you talk about your achievements and future goals. Among best friends from the world of running… at one point or another, you’ll eventually end up talking about poop! Indeed, runner's diarrhea and gastrointestinal problems are somewhat taboo despite the fact that they affect as much as 30 to 50% of endurance athletes. This prevalence even increases to 96% when looking more particularly at ultra-endurance runners. This makes for a rather lively subject of discussion! But what can be done to prevent the onset of gastrointestinal distress?


Nutrition Fodmap


If you have not already done so, you may want to dig in our blog article on the different causes of gastrointestinal problems. This article will provide you with possible solutions in that respect. However, if you have already tried each of these recommendations, to no avail, it might be a good idea to consider another option. I'm talking about the low-FODMAP diet. A diet originally designed to relieve people suffering from irritable bowel syndrome. 


The acronym FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. In short, they are carbohydrates that are partially digested and absorbed by the intestine. These carbohydrates therefore wind up in the colon and ferment there. This is a completely normal process that does not usually cause any adverse digestive effects in most people. However, in people with a more sensitive digestive system, this could exacerbate certain gastrointestinal problems, resulting in bloating, abdominal pain and gas.  In this population of individuals, a low-FODMAP diet generally reduces symptoms with a success rate of around 70%.


In runners, intestinal ischemia that results from reduced blood flow to the digestive system during exercise also weakens the intestine, making it more susceptible to gastrointestinal distress during and after exercise. If, additionally, certain undigested food particles are present, the risks of gastrointestinal problems soar! This results in an increased osmotic load in the small intestine, causing an influx of water into the intestine to dilute excess carbohydrates. This leads to an urgent need to defecate, loose stools or diarrhea. In that respect, following a low-FODMAP diet a few days before an important event, as well as during an event spanning several hours or days, could prove beneficial for more sensitive runners.


Although research on the low-FODMAP diet among endurance athletes is relatively recent, results already support such an approach in order to minimize gastrointestinal distress during exercise. Several athletes have reported having removed from their diet certain FODMAP-rich foods without actually being aware of this approach. Foods containing lactose are most often removed by athletes with gastrointestinal problems, followed by foods containing a lot more fructose than glucose (e.g., honey, cherries, watermelon). Up to date, only a few case studies as well as a small number of intervention studies have been carried out using the FODMAP approach in runners and results are promising. In a first case study, following a low-FODMAP diet 6 days before as well as during a multistage mountain ultramarathon (186.7 km over 6 days of running) significantly reduced digestive distress in a female runner. Reported symptoms were limited to mild bloating and flatulence during the race while the athlete had reported significant gastrointestinal symptoms during training. In addition, a 6-day low-FODMAP diet significantly reduced gastrointestinal symptoms in a male triathlete compared to an identical training period with a high-FODMAP diet. Although these results are very interesting, the fact remains that the sample size is pretty small! General recommendations can’t be issued before controlled intervention studies are published.

In this context, a first intervention study was carried out with 11 runners reporting persistent gastrointestinal distress. The latter were subjected to a protocol involving two 6-day training phases. During these phases, runners were given alternately a high- and low-FODMAP diet, without knowing in which order they were provided. At the end of the study, 9 out of 11 athletes reported less daily gastrointestinal symptoms while eating the low-FODMAP diet. No difference was observed between the two groups during the prescribed training sessions. In a second intervention study carried out with 16 recreational runners who had to follow a high- and low-FODMAP diet for 7 days (interspersed with a 7-day break between the two menus), 69% (11) of participants reported a positive effect on their gastrointestinal symptoms while they were following the low-FODMAP diet.


These studies covered a short period of time and were carried out with a limited number of subjects. However, they do support the hypothesis that a low-FODMAP diet could prove beneficial for runners struggling with persistent gastrointestinal symptoms. Such diet can therefore be beneficial on an ad hoc basis before an important event in order to prevent unpleasant surprises during a race. Longer-term applications can also be considered, particularly in intensive training phases. The purpose is not to remove high-FODMAP foods altogether, but rather to remove those that cause such symptoms during more sensitive periods of the year when you are training and in competition.


Below is a table listing high-FODMAP foods commonly used in a runner's diet as well as low-FODMAP alternatives.  Please note that it is best to consult a health care professional if you plan to adopt a low-FODMAP diet for an extended period or if you suffer from persistent gastrointestinal distress.


High-FODMAP Foods Regularly Consumed by Athletes


nutrition fodmap

Isabelle Morin