• Simone do Carmo // MSc Physiology

GI Distress and The Low-FODMAP Athlete

After months of training, the last thing any athlete would want to deal with is gastrointestinal (GI) distress during a race. GI distress can have many adverse effects on performance and recovery and is probably the most common complaint among endurance athletes, with studies showing a prevalence ranging from 30% up to 90%![1] The large variation in prevalence is likely explained by the different methodologies of studies and other factors including study population, the exercise modality and environmental conditions. Nonetheless, this shows that GI distress is a real problem in the sporting world.

GI distress is not fully understood and the wide range of reported symptoms makes it a difficult problem to treat as a sports dietician or nutritionist. Symptoms are generally classified as either upper GI symptoms (e.g. heartburn, bloating, nausea) or lower GI symptoms (e.g. cramps, diarrhoea, intestinal bleeding), with the latter being associated with more severe cases[1]. A study by Stuempfle, et al.[2] showed that more than half of ultra-marathon runners experienced GI distress with nausea being the most prevalent symptom (85%), followed by cramps, diarrhoea and vomiting. There also seems to be a genetic predisposition to developing GI distress as Pfeiffer, et al.[3] demonstrated a strong correlation between GI complaints and having a family history of GI symptoms.

The causes of GI distress can be divided into three categories: physiological, mechanical and nutritional[1]. GI ischemia is often recognised as the main physiological mechanism but there are others including changes in gut function due to a reduction in blood flow and increased intestinal permeability. Anxiety and stress are also common contributors to changing gut function, which may interfere not only on race day but also with an athlete’s daily training. Mechanical causes are typically related to a change in posture, common in cycling due to increased abdominal pressure, or repetitive impact during running which may damage the lining of the intestine. This damage combined with reduced blood flow is thought to be the cause of intestinal bleeding, the most common symptom experienced by long-distance runners.

In terms of nutritional factors, dehydration and consuming high-fibre, high-fat, high-protein, fructose, milk and highly-concentrated carbohydrate drinks have all been associated with a greater risk of developing GI distress and should be taken into account when preparing for a race[1]. In some athletes, abdominal symptoms such as flatulence and altered bowel movements may be triggered by certain foods that are not so well absorbed and are rapidly fermented in the gut. These foods are known as FODMAPs, which is an acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols, and reducing their consumption may help manage an athlete’s symptoms. Common high-FODMAP foods include:

  • High-fructose corn syrup and high-fructose fruits, such as apples, pears and mangos;

  • Lactose-containing foods, such as milk, yoghurt and cheese;

  • Legumes, lentils and chickpeas;

  • Polyols (known as ‘sugar alcohols’) which include sugar-free sweeteners and foods such as avocados, mushrooms, apples and cherries;

  • Foods that contain fructans, such as onions, leeks, garlic, wheat and rye.

A low FODMAP diet was initially developed for patients who suffer from Irritable Bowel Syndrome (IBS) by an Australian dietician Dr. Sue Shepard[4]. It has also been applied to other conditions such as coeliac disease, fructose malabsorption, and both gluten and lactose intolerances. Many commercially available sports products such as sport drinks, gels and bars are common nutritional practices during a race but the majority contain FODMAPs and are often associated with symptoms developing during a race. Rehrer, et al.[5] examined the relationship between dietary practices and the development of GI distress symptoms in 55 male triathletes who took part in an half-Ironman race. Fifty-two percent revealed an urge to defecate while 42% complained of flatulence. Other symptoms included vomiting, abdominal pain, nausea, diarrhoea and intestinal cramps and more of these symptoms occurred during running. Ninety-three percent of triathletes consumed a hypertonic drink and 40% of those had severe complaints compared to only 11% who consumed a hypo- or isotonic drink. All triathletes who complained of intestinal cramps had consumed high-fibre foods before the race and those who vomited, or felt the urge to do so, had eaten foods high in fat and protein.

More and more athletes are realising that a low FODMAP diet can help manage their symptoms, allowing them to focus on their performance rather than their unpredictable gut. A recent case-study[6] implemented a short-term, low-FODMAP dietary intervention to help a male athlete manage his GI symptoms during running. His habitual diet was compared to a 6-day, low-FODMAP diet while keeping his training similar in both conditions. The athlete’s GI symptoms were recorded immediately post-exercise and at the end of each day. His Daily Analysis of Life Demands for Athletes (DALDA) scores were also recorded. The DALDA is a self-reported and validated questionnaire that measures an athlete’s response to stress related to daily life and training. On a scale from 0 to 9, the athlete’s post-exercise and daily GI symptoms scores ranged from 0 to 4 during his habitual diet. In contrast, during the low-FODMAP diet, his scores were all 0. The athlete’s DALDA scores also showed improvement during the low-FODMAP diet condition. Although more research, specifically randomised-controlled trials, is clearly needed to examine the effectiveness of a low-FODMAP diet in managing GI distress symptoms in athletes, this does not discount the n=1 effectiveness of a short-term, low-FODMAP diet as each athlete’s nutritional situation is unique and should be treated as such.

Another thing to remember is that the gut is an adaptable organ, therefore practising nutritional strategies during training is not only key to determining what may work best for an athlete but it can also enhance gut function and improve its tolerance to certain foods. A calm gut means a happy athlete!

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

  2. Stuempfle KJ, Hoffman MD, Hew-Butler T. Gastrointestinal distress in ultramarathoners is associated with race diet. Int J Sport Nutr Exerc Metab. 2013; 23:103–109.

  3. Pfeiffer B, Stellingwerff T, Hodgson AB, et al. Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc. 2012; 44:344–351.

  4. The Low FODMAPS Diet <https://www.sportsdietitians.com.au/factsheets/diets-intolerances/the-low-fodmaps-diet/> [Accessed 14 July 2016].

  5. Rehrer NJ, van Kemenade M, Meester W, et al. Gastrointestinal complaints in relation to dietary intake in triathletes. Int J Sport Nutr. 1992; 2:48–59.

  6. Lis, DM, Ahuja, KD, Stellingwerf, T, Kitic, CM, Fell, J. Case Study: Utilising a Low FODMAP Diet to Combat Exercise-Induced Gastrointestinal Symptoms. Int J Sport Nutr Exerc Metab. 2016 [Epub ahead of print].



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