Individuals competing in endurance events frequently notice gastrointestinal (GI) distress with common features including nausea, flatulence, bloating and stomach pain.1 Depending on the criteria of symptomology used along with research methodology, the prevalence of GI distress during exercise has been estimated in 30-90% of athletes.2 Such symptoms can be defined as ‘exercise-induced gastrointestinal syndrome’ which tend to be more prevalent in running, hot and humid conditions, high intensities and over a threshold of 2 hours of exercise.1
Such gastrointestinal symptoms may range from mild such as light gas to severe which prevents the exercise session from being completed.3 Symptoms can be classified into upper GI tract including bloating, vomiting and nausea, or lower GI tract including flatulence, stich, and cramping.1
Cause of gastrointestinal issues during exercise
While the exact cause is unknown and it likely to be multifaceted, a reduced blood flow through the gut has been indicated as a main mechanism. 4 5 When we begin endurance exercise such as running or cycling, blood looks to move away from the splanchnic organs (i.e stomach, small intestine and large intestine) and towards the working muscles (i.e arms and legs), to provide the muscle with oxygen and nutrients. The lack of oxygen to the GI tract, also known as hypoperfusion, creates damage and inflammation to the gut lining leading to onset of GI symptoms.4
How can I reduce such gastrointestinal issues through nutrition?
This has led to an increase to research potential strategies to reduce exercise-associated GI symptoms. Multiple dietary management strategies have been investigated.
• Avoiding exercising in a dehydrated state6
• Training the gut to tolerate carbohydrates7
• Limiting foods with a high fat and high fibre content before exercise1
The above recommendations all look to decrease the severity of GI issues when undertaking endurance exercise.
Recently, a more novel strategy of FODMAP reduction have been investigated. A reduction in FODMAP content has gained popularity and supporting evidence as a promising dietary tool to reduce GI symptoms in healthy adults who suffer from exercise-induced gastrointestinal syndrome where similar symptoms are reported to IBS patients (e.g. bloating, nausea, urge to vomit).1,8 A low FODMAP diet is the preferred strategy used in the treatment of symptomatic irritable bowel syndrome (IBS) with 70% of patients reporting symptom reduction.9
What are FODMAPs?
FODMAPs are short chain carbohydrates found in a wide range of food products including fruits, vegetables, cereals and more.10
An acronym which stands for:
Fermentable Bacteria in the gut ferments undigested carbohydrates and therefore gas is produced
Oligosaccharide Fructans and galactooligosaccharide for example, onions, garlic, some legumes and pulses. Low FODMAP alternatives include broccoli, black beans and chickpeas,
Disaccharide Lactose for example, dairy products such as milk, yoghurt and cheese. Low FODMAP alternatives include lactose-free dairy such as soya products.
Monosaccharide Fructose for example, honey, apples and watermelon. Low FODMAP alternatives include oranges, pineapple and strawberries,
Polyols Sorbitol and Mannitol for example, artificial sweeteners. Low FODMAP alternatives include maple syrup and table sugar.
The MONASH website has a great information page all about foods high and low in FODMAPs.
How do FODMAPs cause GI symptoms?
Short chain carbohydrates found in foods high in FODMAPs draw water into the small intestine and increase the osmotic load. FODMAPs are not completely digested or absorbed by the intestine so when passing into the large intestine, fermentation by gut bacteria causes FODMAPs to produce gas as a result. Thus, the onset of GI symptoms.11
Researchers noted a lower prevalence of GI symptoms in runners (82%) with persistent self-reported GI problems during a low FODMAP intervention period.12 With further case studies encouraging the implementation of a low FODMAP diet in individuals with GI problems.13, 8
Who should follow a low FODMAP diet?
If you are suffering from exercise-induced gastrointestinal issues, a modified FODMAP may help to reduce such issues. It is important to consult a qualified nutritionist/dietitian with experience in sports nutrition and/or gut disorders such as IBS before undertaking a change to the diet. This is important as severe or persistent cases of GI distress might be diagnosed as a functional GI disorder. Additionally, self-prescribed low FODMAP diets have the potential to be incredibly restrictive, often neglecting food groups putting individuals at a health and performance risk14 with restriction for a prolonged period negatively impacting gut microbiota and reducing short-chain fatty acid production.15
Overall, GI symptoms are prevalent amongst many individuals who partake in exercise, with symptoms ranging from mild to severe. Modification of food intake including undertaking a reduced FODMAP diet may reduce the risk of GI discomfort during exercise.
This blog post was written by Molly Wisbey who has recently finished her Masters degree in Sports Nutrition at Liverpool John Moores University after undertaking BSc in Nutrition at Oxford Brookes University. Molly has set up her own nutrition freelance services, specialising in sport, where she supports and coaches a variety of clients. Molly is currently taking on new clients and would be delighted to hear more from you. Molly can found on Instagram @fuellingperformancewith_mol and on twitter @wisbey_molly.
(1) Costa et al. (2017). Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Aliment Pharmacol Ther, 46(3), 246-265. doi:10.1111/apt.14157.
(2) De Oliveria, E., Burini, R and Jeukendrup., A. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine. 44 (Suppl 1), pp: 79-85.
(3) Pugh, J. N., Kirk, B., Fearn, R., Morton, J. P., & Close, G. L. (2018). Prevalence, Severity and Potential Nutritional Causes of Gastrointestinal Symptoms during a Marathon in Recreational Runners. Nutrients, 10(7). doi:10.3390/nu10070811
(4) Jeukendrup, A. E., Vet-Joop, K., Sturk, A., Stegen, J. H. J. C., Senden, J., Saris, W. H. M., & Wagenmakers, A. J. M. (2000). Relationship between gastro-intestinal complaints and endotoxaemia, cytokine release and the acute-phase reaction during and after a long-distance triathlon in highly trained men. Clinical Science, 98(1), 47-55. Doi 10.1042/Cs19990258.
(5) Otte, J. A., Oostveen, E., Geelkerken, R. H., Groeneveld, A. B., & Kolkman, J. J. (2001). Exercise induces gastric ischemia in healthy volunteers: a tonometry study. J Appl Physiol (1985), 91(2), 866-871. doi:10.1152/jappl.2001.91.2.866.
(6) Snipe, R., Khoo, A., Kitic, C., Gibson, P and Costa, R. (2018). The impact of mild heat stress during prolonged running on gastrointestinal integrity, gastrointestinal symptoms, systemic endotoxin and cytokine profiles. International Journal of Sports Medicine. 39, pp: 255-263.
(7) Costa et al. (2017a). Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Appl Physiol Nutr Metab, 42(5), 547-557.doi:10.1139/apnm-2016-0453.
(8) Lis, Ahuja, Stellingwerff, Kitic, & Fell. (2016a). Case Study: Utilizing a Low FODMAP Diet to Combat Exercise-Induced Gastrointestinal Symptoms. Int J Sport Nutr Exerc Metab, 26(5), 481-487. doi:10.1123/ijsnem.2015-0293
(9) Stuempfle, K. J., & Hoffman, M. D. (2015). Gastrointestinal distress is common during a 161-km ultramarathon. J Sports Sci, 33(17), 1814-1821.
(10) Gibson, P. R., Muir, J. G., & Newnham, E. D. (2015). Other Dietary Confounders: FODMAPS et al. Dig Dis, 33(2), 269-276. doi:10.1159/000371401.
(11) Gibson, P. R., & Shepherd, S. J. (2010). Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. J Gastroenterol Hepatol, 25(2), 252-258. doi:10.1111/j.1440-1746.2009.06149.x
(12) Lis, Stellingwerff, Kitic, Fell, & Ahuja. (2018). Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in Athletes. Med Sci Sports Exerc, 50(1), 116-123.doi:10.1249/MSS.0000000000001419.
(13) Gaskell, S. K., & Costa, R. J. S. (2019). Applying a Low-FODMAP Dietary Intervention to a Female Ultraendurance Runner With Irritable Bowel Syndrome During a Multistage Ultramarathon. Int J Sport Nutr Exerc Metab, 29(1), 61-67. doi:10.1123/ijsnem.2017-0398.
(14) Hill, P., Muir, J. G., & Gibson, P. R. (2017). Controversies and Recent Developments of the Low-FODMAP Diet. Gastroenterol Hepatol (N Y), 13(1), 36-45.
(15) Halmos, E. P., Christophersen, C. T., Bird, A. R., Shepherd, S. J., Gibson, P. R., & Muir, J. G. (2015). Diets that differ in their FODMAP content alter the colonic luminal microenvironment. Gut, 64(1), 93-100. doi:10.1136/gutjnl-2014-307264
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