Introduction to Gastrointestinal Issues and Physical Well-being in Athletes

Over the past decade, the conversation of the gut microbiota and its positive impact on sports performance has been increasing considerably (Wosinska et al., 2019). At the same time, the recorded number of athletes experiencing gastrointestinal (GI) disturbances has also been on the rise, with up to 90% of athletes enduring debilitating symptoms that negatively impact the ability to compete, achieve sports performance goals and maintain physical well-being (Pugh et al., 2018). Such statistics emphasise the need to manage GI issues in athletes to optimise health and well-being and support them in maintaining high performance in sports.

Whilst GI issues can be experienced regardless of the sports discipline, the prevalence and severity of gut-issues worsen with increasing duration and intensity of exercise, with GI complaints most common amongst endurance athletes (Coleman., 2019; de Oliveira et al., 2014). The symptoms experienced are likened to Irritable Bowel Syndrome (IBS); abdominal pain and bloating, diarrhoea, nausea and vomiting, increased flatulence and feelings of incomplete evacuation, all of which can be influenced by nutritional (dietary-related), physiological (blood flow, inflammation, motility), mechanical (positioning or motion during sport i.e. cycling) and psychological factors (stress, anxiety) (Parnell et al., 2020).

However, an often-overlooked cause of GI issues stems from the gut microbiome. An imbalance of the intestinal microbiota, called dysbiosis, is strongly associated with GI disturbances, including those of a functional nature such as IBS (Chang & Lin, 2016). Dysbiosis can lead to alterations in gut motility and transit times, and increase intestinal permeability, which could cause or exacerbate GI issues (Chang & Lin, 2016). Furthermore, dysbiosis can be driven by infection or inflammation, often seen in athletes due to high physical demands, and by high-protein, often low-carbohydrate diets which can decrease the prevalence of beneficial gut bacteria and their metabolites (Alou et al., 2016). Together these contribute to further digestive discomfort and compromise an already vulnerable immune system (Levy et al., 2017).

Evidence suggests that engaging in moderate intensity exercise regularly can promote gut microbial diversity and enhance the immune system (Markowiak-Kopec & Slizewska, 2020). Increased levels of beneficial gut bacteria, such as bifidobacteria, are likely to be key drivers of positive immunomodulatory effects associated with a healthy and diverse gut microbiome. Bifidobacteria and their metabolites (e.g., short chain fatty acids (SCFA)) have been shown to directly interact with immune cells and modulate specific pathways related to immune function (Ruiz et al.,2017). However, by contrast, physical stress caused by long duration and high-intensity exercise has been linked to an increased risk of dysbiosis and, therefore, GI issues in elite athletes. Furthermore, intensive training loads and competition can compromise the immune system, potentially leading to an increased likelihood of other illnesses, such as upper respiratory tract infections (URTI) (Clark & Mach, 2016; Gleeson et al., 2011; Rico-González et al., 2021). The incidence of UTRI could further disrupt physical well-being of athletes, and their ability to consistently perform at the highest level.

Another emerging area of interest is the link between dysbiosis and alterations in brain function, thought to be mediated by a 2-way communication system between the gut and the brain – referred to as the gut-brain axis. Gut microbiota dysbiosis can result in a heightened incidence of anxiety and depression due to this connection (Chen et al., 2013). These conditions are seen in up to 60% of athletes due to the stress of high training loads and competitive event preparation but may also be further exacerbated by dysbiosis (Clark & Mach, 2016). Anxiety and depression can also lead to an increased incidence of GI disturbances and immune dysfunction, which too may negatively impact sports performance (Clark & Mach, 2016).

So, what are the current strategies used for managing GI complaints in athletes?

Current Recommendations

1. Low FODMAPs

FODMAPs (Fermentable, Oligo-saccharides, Di-saccharides, Mono-saccharides and Polyols) are short chain carbohydrates that are not readily absorbed by the small intestine (Hill et al., 2017). Due to their osmotic effect, foods containing FODMAPs draw water into the large intestine before being rapidly fermented by colonic bacteria (Hill et al., 2017). This can result

in increased gas production and water load, leading to flatulence, bloating, abdominal cramping and diarrhoea (Hill et al., 2017). Whilst studies have demonstrated that up to 86% of people with IBS experience an improvement in symptoms after following a low FODMAPs (LFD) diet, the diet is often restrictive and can lead to significant reductions in beneficial gut bacteria which could then compromise GI health, immunity, and negatively impact nutritional status long-term (Geary et al., 2016). A study by Wilson et al (2020) found that an LFD combined with prebiotic Bimuno galacto-oligosaccharides (GOS) supplementation significantly improved symptom relief in a cohort of IBS patients compared to LFD only (67% vs. 50% of symptom relief, respectively, however, this did not prevent the reduction in bifidobacteria). Current guidelines suggest an LFD is not appropriate for long-term use (Geary et al., 2016), however, followed for up to 2-weeks prior to a competitive event may support athletes in managing their GI issues (Lis & Gaskell, 2020).

2. Low-Residue Diet

A low-residue diet is one which limits indigestible fibre. For many athletes, this means avoiding or significantly limiting key food groups such as whole grains, dairy and vegetables. The guidelines suggest following a low-residue diet for 3-4 days prior to an event to reduce stool quantity and frequency, and therefore, minimise diarrhoea and urgency (Lis & Gaskell, 2020). Whilst there is limited research on low-residue diets, evidence suggests it could also reduce bloating, flatulence and abdominal cramping (Lis & Gaskell, 2020). However, as fibre is an important element for gut microbiota-mediated health, limiting consumption has shown to reduce microbial diversity and minimise beneficial gut bacteria needed for optimal GI health and immunity (Akçakaya., 2020).

3. Limiting Caffeine

Caffeine is often recommended to athletes due to its positive impact on sports performance (Clark et al., 2018). However, caffeine consumption has been shown to increase colonic motility which increases the likelihood of diarrhoea, urgency and abdominal cramping (Zach, 2021). Studies have demonstrated that morning caffeine intake is associated with lower-GI symptoms experienced during physical activity, which become even more pronounced during

a long-duration event (Wilson, 2016). Therefore, avoiding caffeine entirely on the day of an event may mitigate these issues.

4. Gut-Tolerance training

Training shortly after eating or after water consumption can often elicit GI disturbances in athletes, such as nausea, vomiting, abdominal cramping and reflux (Burke, 2019). This is particularly true after carbohydrate consumption, often consumed pre-workout to provide slow-releasing energy (Burke, 2019). Gut-tolerance training is a protocol whereby the GI system is trained to tolerate gradual increases in the amount of carbohydrate and fluid over time in an attempt to minimise GI distress (Jeukendrup, 2017). Studies have indicated that gut-tolerance training can improve gastric emptying and absorption and reduce the incidence and severity of GI symptoms during endurance exercise, thus having a positive impact on performance (Jeukendrup, 2017; Costa at al 2017; Miall et al, 2018). However, more human studies are required to develop the most effective strategies to induce gut adaptations from this type of “nutritional training” (Jeukendrup, 2017).

5. Gluten-Free Diet

A gluten-free diet aims to eliminate all cereal products and grains that contain the wheat protein, gluten (Cialdella-Kam et al., 2016). As many as 40% of athletes follow a gluten-free diet up to 4-weeks before an event, with the presumption that it may enhance sports performance or reduce GI symptoms (Lis et al., 2015). However, there is little evidence that following a gluten-free diet has any effect on GI distress or sports performance in non-clinical (non-coeliac) populations (Lis et al., 2015). A gluten-free diet has repercussions for the microbiome; reducing bacterial richness and diversity which could lead to dysbiosis and further exacerbate GI symptoms or compromise immunity (Dionne et al., 2018).

6. Probiotics

The International Scientific Association for Probiotics and Prebiotics (ISAPP) define probiotics as “live micro-organisms that, when administered in adequate amounts, confer a health benefit to the host” (ISAPP, 2018a). Whilst probiotics have multiple health-related uses, they are often recommended to athletes to reduce GI distress and enhance immune function

(Galdeano et al., 2019). Studies have demonstrated that the frequency and severity of GI symptoms are improved with probiotic supplementation, with their efficacy increasing with long-term supplementation (Miles, 2020). Furthermore, they have the ability to activate protective immune mechanisms to support immunity (Galdeano et al., 2019). This is thought to be due to a restoration of microbial diversity and an increase in beneficial species of bacteria, such as Lactobacillus and Bifidobacterium (Miles., 2020). However, newer studies suggest that the efficacy of probiotics can be increased with the additional use of prebiotics, a newer and developing approach, called synbiotics, to managing GI issues (Li et al., 2020).

Novel Approaches: Prebiotics

Prebiotics, also known as “gut fertilisers”, are specific groups of indigestible nutrients, often dietary fibres (Davani-Davari et al., 2019). The ISAPP define prebiotics as “substrates that are selectively utilised by host micro-organisms conferring a health benefit” (ISAPP, 2018b). Upon reaching the large intestine, prebiotics are fermented via the microbiota to produce SCFAs and other metabolites, which can increase the integrity and reduce inflammation of the gut epithelium, provide energy to colonocytes, and limit the growth of pathogenic bacteria (Alexander et al., 2019; Davani-Davari et al., 2019; Sivaprakasam et al., 2016).

Whilst prebiotics exist in various foods naturally, normally in smaller quantities, nutritional experts often recommend adding a prebiotic supplement into the diet to offset any potential deficiency or support a particular health issue where there is evidence to suggest an improvement. However, a food-first approach should always be recommended before supplementation is considered. The two most common prebiotic supplements are fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS). Studies using Bimuno GOS supplementation, have seen a significant reduction in IBS-like symptoms, such as abdominal cramping, faecal urgency, bloating and flatulence after 2-weeks of supplementation (Vulevic et al., 2018). This is likely to be attributed to increased bifidobacteria in the gut within 7 days of daily supplementation (Depeint et al., 2008; Huaman et al., 2018). Whilst these studies have not been conducted in athlete populations, the beneficial effects of GOS-based supplementation may translate into optimal GI health for elite athletes.

Additionally, Bimuno-GOS prebiotic supplementation has been shown to improve immunity (Vulevic et al., 2008; Vulevic et al., 2013) and decrease circulating pro-inflammatory cytokines associated with URTI in athletes (Williams et al., 2016), reduce anxiety and improve quality of life in those suffering from IBS (Silk et al., 2009). Such evidence suggests that Bimuno-GOS prebiotic supplementation could be an effective strategy to support athletes in further managing their GI issues, as well as positively impact their immunity and recovery from demanding physical activity.

Future Research and Concluding Remarks

GI issues in athletes are often debilitating and compromise overall physical health and well-being. These issues also negatively affect the ability to train and compete, both individually and within team sports. Whilst many nutritional-focused strategies exist, prebiotic supplementation is an emerging, novel approach for potentially managing uncomfortable GI symptoms and enhancing immunity in this population. As many studies looking at prebiotic supplementation focus on non-athlete populations, future research should attempt to understand more about the effect of prebiotics in athletes, and how this in turn impacts sports performance – specifically thinking about mechanisms of action to better inform how to implement an effective prebiotic strategy. Furthermore, understanding the differences in GI symptoms and how these are affected by prebiotics across the individual sports disciplines is essential for enhancing well-being across all sporting populations using a tailored approach.

by Roisin Pichon as part of a working experience programme at Clasado Biosciences

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