Low FODMAP diets as a dietary prescription for reducing exercise-induced gastrointestinal symptoms during endurance exercise

Rachel Scrivin

doi:10.25907/00942

It is well established that endurance exercise can disrupt gastrointestinal integrity and function, which may lead to systemic immune responses and exercise-associated gastrointestinal symptoms (Ex-GIS), a condition referred to as exercise-induced gastrointestinal syndrome (EIGS). Many endurance athletes report Ex-GIS during competitions, varying from mild discomfort to severe. Many of the Ex-GIS experienced by athletes, including abdominal pain, bloating, flatulence, and/or a change in stool consistency, are similar to those reported by people with irritable bowel syndrome (IBS). A well-known treatment for IBS is a low fermentable oligo-, di-, monosaccharide and polyol (FODMAP) diet, which reduces symptoms by up to 75% and improves the quality of life in those with IBS. FODMAPs are short-chain carbohydrates (e.g., lactose, excess fructose, oligosaccharides (fructo-oligosaccharides and galacto-oligosaccharides) and polyalcohols), which are osmotically active and draw water into the intestine, increasing luminal contents. FODMAPs are also highly fermentable by colonic microbiota, producing gas and short-chain fatty acids. The additional luminal contents and intestinal gas can lead to IBS symptoms. Preliminary evidence suggests athletes are using low-FODMAP diets to manage Ex-GIS, yet further research is needed to confirm the impact on symptom relief and associated performance implications. The possible rationale for athletes with Ex-GIS trialling low-FODMAP diets is likely due to the synergies in gastrointestinal symptoms experienced by those with IBS. A further consideration is that sports nutrition guidelines recommend endurance athletes increase their carbohydrate intake 36 – 48-h before exercise to improve athletic performance. By increasing carbohydrate intake, dietary FODMAP intake is also likely to increase due to many carbohydrate food sources containing high dietary FODMAP loads. The implications of high carbohydrate, low dietary FODMAP loads on EIGS and Ex-GIS development were key research considerations for the current thesis. The thesis consists of nine chapters. Five of the thesis chapters are peer-reviewed published research studies, and another chapter is currently in review. These studies provide rationale and evidence for implementing a low-FODMAP diet to mitigate EIGS and Ex-GIS. Firstly, a validated questionnaire was developed to assess carbohydrate practices and dietary strategies used to manage Ex-GIS. Results indicate that endurance athletes have good carbohydrate knowledge, believe that consuming carbohydrate around exercise enhances athletic performance, and intend to consume more carbohydrate around exercise. Despite a lack of rigorous scientific rationale, many athletes report manipulating their diets to better manage their Ex-GIS, such as trialling a low-FODMAP diet. The preliminary thesis findings helped inform the methodology of a controlled laboratory study. The experimental laboratory study investigated the effects of a 48-h high carbohydrate diet with varied (low and high) FODMAP content before endurance exercise on gastrointestinal integrity, endotoxin translocation, inflammatory and systemic responses, gastrointestinal function, Ex-GIS and subsequent exercise performance. No differences were found between high carbohydrate low-FODMAP (HC-LFOD) or high carbohydrate high-FODMAP (HC-HFOD) diets for physiological strain, gastrointestinal integrity and function, or performance. However, greater incidence and severity of Ex-GIS were reported in the HC-HFOD trial. Subsequent field trials support the application of a 48-h HC-LFOD as most athletes reported reduced incidence and severity of Ex-GIS and improved perceived work output. The final summary chapter of the thesis was a systematic literature review that determined the efficacy of a low-FODMAP diet for reducing Ex-GIS and potential markers of EIGS. The review confirmed that a 24 – 48-h low FODMAP diet before exertional stress is an effective dietary strategy to reduce the incidence and severity of Ex-GIS and can potentially alter EIGS pathophysiology. The thesis findings contribute to the scientific knowledge base in the growing research area of exercise gastroenterology research.

Low FODMAP diets as a dietary prescription for reducing exercise-induced gastrointestinal symptoms during endurance exercise

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