FODMAP and Sports: How to Reduce Stomach Issues

Many athletes encounter gut issues that disrupt both training and competition. This article discusses FODMAP—fermentable carbohydrates that can cause gas, bloating, and gut discomfort—and the impact a low-FODMAP diet can have on athletes. The key question is whether reducing these carbohydrates can help decrease gut problems without affecting performance. The study concludes that many experience less gut discomfort in daily life, though the effect during short, high-intensity sessions is less clear. For athletes with recurring gut issues, it might be worth trying this strategy before longer sessions or competitions.

FODMAP stands for Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which essentially means fermentable carbohydrates and sugar alcohols (polyols).

Foods are categorized based on the amount of FODMAP they contain. These foods and diets can be classified as Low FODMAP (LFOD) or High FODMAP (HFOD). The trend is growing in the USA and is expected to do the same in Sweden — our diet and nutrition trends often arrive here a few years after the USA, so statistically, FODMAP will likely become more recognized in Sweden as well.

Currently, FODMAP is primarily used by individuals with IBS (Irritable Bowel Syndrome). The method was developed in Australia in 2009 as a tool specifically for IBS and Crohn's disease. Now, FODMAP is starting to be applied in sports, which is particularly interesting for those of us who want to perform without the gut interfering.

The study that inspired this article is titled "Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in Athletes" and was published in January 2018 (source). Researchers observed that among athletes experiencing stomach issues, over 50% had previously tried a low-FODMAP diet without realizing it was Low FODMAP—they had independently discovered what eased their gut troubles. Therefore, the researchers confirm: yes, avoiding certain foods seems beneficial, and by classifying them, it's easier for you to know what should be avoided.

86% of athletes who avoid FODMAP report less stomach trouble. That's a significant number and definitely makes it worth trying, in our opinion. We've previously written about Stomach Issues and Runner's Gut if you're interested in learning more about its effects on runners.

In the experimental phase, the researchers enlisted 11 runners (aged 18–50) who ran at least 25 km/week and frequently reported “runner's gut.” Participants started with either Low or High FODMAP for 6 days, followed by a one-day gap during which they ate normally, and then switched to the other diet for 6 days. The study was blinded—the runners were only aware they were comparing two isocaloric “special carbohydrate diets” named diet A or B. The nutritional content of the diets was very similar: 5–7 g carbohydrates, 1.2–1.7 g protein, and 0.8–1.2 g fat per kilogram of body weight.

For a more detailed breakdown, see Table 1.

When participants consumed high amounts of FODMAP, they ingested just over 41 g of fermentable carbohydrates per day, and during the low intake period, they consumed 8 g per day — quite a difference.

The results show that 9 out of 11 people experienced fewer gut issues with Low FODMAP over the 6-day period. Interestingly, they primarily experienced fewer stomach problems in daily life; however, there was no difference between the periods on the tougher training days (5×1000 m with 3 min rest and 7 km threshold run).

So: FODMAP may not be a magic solution for shorter, high-intensity workouts, but for longer or everyday situations, there's clear support that it can make a difference. Let's dive deeper.

FODMAP is essentially about avoiding carbohydrates that ferment and produce gases, as well as causing irritation in the stomach/gut. Foods you are advised to avoid 1–3 days before training or competition include:

• Onions / garlic
• Dairy products containing lactose (this does not apply to lactose-free products)
• Wheat-based foods
• Stone fruit (apricot, mango, nectarine, peach, plum, cherry)
• Candy and confectionery containing sugar alcohols. Watch out for sorbitol, mannitol, maltitol, xylitol, isomalt, lactitol, and erythritol.

All of these foods contain high levels of fermentable carbohydrates and can therefore increase the risk of stomach issues.

Sugar alcohols are not only fermentable and gas-forming — they also draw fluid into the intestines and can lead to looser stools. It often says as a warning on products containing sugar alcohols that high consumption has a laxative effect. A simple tip before competition: if the package says “laxative effect” — don’t eat it.

An interesting aspect of this study is that the runners did not experience a calmer gut during interval or threshold sessions (i.e., two high-intensity sessions, approximately 90–100% VO2max), while 82% of them reported a calmer gut in everyday life. I speculate that with a larger study population or longer, more relaxed sessions (like classic long runs of 1.5 hours or more), there could have been a statistically significant result for those training sessions as well.

The researchers note that a healthy population without gut issues is unlikely to notice significant differences from excluding high-FODMAP foods. However, as a long-distance athlete, where the risk of gut troubles increases the longer you run, it might be beneficial to experiment. Try this: start by excluding dairy products and onions 2 days before training. Then eliminate wheat-based products, stone fruits, etc. If you notice a calmer gut that handles sports drinks and nutrition better, you've suddenly added an important piece to an effective energy plan before a competition.

In this study, participants did not use carbohydrates during training because the sessions were too short (maximum 30 min). However, it would be very interesting to study longer training sessions or competitions where sports nutrition is actually used during activity.

The full-length study