It is now well accepted that gut complaints during and after exercise are a common issues amongst athletes (Read more here). The primary causes are changes in blood flow to the gut, stress responses, and mechanical impacts on the gut, in response to exercise per se. In addition, these exercise associated gut complications can be made worse by a wide array of factors within the exercise scenario (Read part 1 here).
Strategic pathway to identify causal factors and manage gut complication and complaints during and after exercise in athletes.
Gastro-intestinal problems need thorough assessment
A substantial amount of anecdotal evidence from sport and exercise nutrition practitioners report athletes’ frustrations in attempting multiple prevention and management strategies (e.g., food and fluid quantity and quality, manoeuvre techniques, hydration, food restriction or avoidance, supplementation, etc…), in a ‘trial and error’ fashion, without any consistent positive results and/or sporadic improvement across a large number of events. Considering the diverse factors that will cause gut issues in athletes, it is clear that ‘one size’ does not fit all, and that an athlete tailored intervention (i.e., applying appropriate and effective strategies to reduce gut complications and complains during and after exercise) is warranted after thorough assessment. This may include understanding the background history of an athlete’s recurrent gut issues, undertaking a gut assessment during exercise to identify the cause and factors that worsen the gut complications and complaints during exercise, blood tests, or more specialised diagnostic testing such as gut motility, gut microbiota composition, food allergy or intolerance investigation.
In the last 5 years there has been an exponential increase in research into prevention and management strategies of gut complications and complaints in athletes. The most promising strategies have included:
Carbohydrate consumption before and during exercise, within individually tolerable limits, has been shown to prevented exercise causing damage to gut cells, and does not cause any accentuated gut discomfort above water (2). Protein (i.e., whey isolate) at the same rate results in similar gut damage prevention benefits, but results in substantially more gut discomfort (2).
Gut-training by challenging the gut with high content and volume of carbohydrates has been shown to improved carbohydrate malabsorption, improved glucose availability into the blood, and substantially reduced gut discomfort, which translated into improve running performance, (1). (Link)
The role of fermentable oligo- di- mono-saccharides and polyols (FODMAP) in managing athletes gut complications during around exercise has been previously covered (link). Recent research revealed that a 24h low FODMAP (2g/day), compared with a high FODMAP (47g), energy and nutrient matched diet, was sufficient to reduced gut complications during endurance running in the heat, by reducing the degree of carbohydrate malabsorption before starting exercise. An interesting finding was that the low FODMAP diet also induced greater gut cell injury and greater disturbance to the gut-blood barrier compared with the high FODMAP diet. The protective effect of a high FODMAP diet on gut cells and gut-blood barrier may lay with its influence on changing the gut microbiota composition (e.g., commensal vs. pathogenic bacteria profile) (3).
Other potential beneficial strategies:
Starting and maintained hydration throughout exercise may protect against gut cell damage and carbohydrate malabsorption compared with dehydration. But forcing fluid consumption to maintain hydration may lead to exaggerated gut complications due to stomach overload. A balance is needed between hydrating and tolerance (4).