Gut Health for Athletes: Training, Racing and Recovery

Medically reviewed and written by Dr Zeeshan Afzal, MBBS — Medical Content Lead, Welzo. Last updated: July 2026. Next review: July 2027.

Ask any experienced endurance athlete about their worst race and there is a good chance the story involves their stomach rather than their legs. Cramping on the bike leg. Sprinting for a portaloo at mile 18. Being unable to swallow another gel with 40km still to run. For a large proportion of athletes, the digestive system — not the cardiovascular system — is the organ that fails first. This matters more than most training plans acknowledge. Your gut is the organ that absorbs the carbohydrate that fuels your race, the water and electrolytes that keep you hydrated, the protein that rebuilds your muscle, and the micronutrients that underpin immunity. It also houses roughly two-thirds of your immune tissue and a microbial community that appears to be genuinely different in trained athletes compared with sedentary people. This guide covers what the evidence actually shows about gut health for athletes — the physiology of exercise-induced gut disturbance, what the athlete microbiome research does and does not prove, how to train your gut for higher fuelling rates, how to build a race-day plan that does not backfire, and which supplements have credible support. If you want to explore products alongside the reading, Welzo's gut health range and probiotics collection are the two main starting points, with targeted options including Akkermansia muciniphila, modified citrus pectin powder, Welzo Ultra Purity Berberine and Welzo Ultra Purity TUDCA. For the wider context, our pillar guides on gut health in the UK, gut barrier function, microbiome diversity and short-chain fatty acids give the underlying biology, and runner's trots covers the single most common complaint in this article.

Image: "Marathon Runners" by Chris Brown, via Wikimedia Commons, CC BY 2.0.

Table of contents

• Why gut health matters for athletes
• Exercise-induced gastrointestinal syndrome explained
• The athlete microbiome: what the research shows
• Common gut symptoms in athletes and what they mean
• Building a resilient gut in the training block
• Training the gut: raising carbohydrate tolerance
• Race day: a gut-friendly fuelling protocol
• Recovery: repairing the gut after hard efforts
• Low FODMAP for athletes: when and how
• Supplements: what the evidence supports
• Testing and when to see a doctor
• Special considerations by athlete group
• An eight-week gut plan for athletes
• Frequently asked questions
• References

Why gut health matters for athletes

There are four distinct reasons the gut deserves a place in an athlete's programme, and they are often confused with one another.

1. The gut is the delivery system for fuel

Carbohydrate eaten during exercise has to survive the stomach, empty at a usable rate, be absorbed across the small intestine and reach the bloodstream before it can power a muscle. Every one of those steps is a potential bottleneck. Asker Jeukendrup's review of gut training makes the point directly: the gastrointestinal tract is a major determinant of endurance performance, and it is highly adaptable to the demands placed on it.

2. The gut is a barrier

A single layer of epithelial cells separates the contents of your intestine from your bloodstream. Hard exercise transiently loosens that barrier. When it loosens too much, bacterial fragments can cross into circulation and trigger an inflammatory response — the mechanism that links prolonged effort in the heat with systemic symptoms and, in rare cases, exertional heat illness. Our guide to gut barrier function covers this in depth, and is leaky gut real? addresses where the popular term diverges from the science.

3. The gut is an immune organ

Heavy training blocks are associated with increased upper respiratory symptoms, and the gut-associated lymphoid tissue is a central player in that relationship. See gut health and the immune system for the mechanisms.

4. The gut is a metabolic organ

Gut bacteria ferment fibre into short-chain fatty acids — mainly acetate, propionate and butyrate. Butyrate is the preferred fuel of the colonic lining. Propionate is a gluconeogenic substrate. These are not trivial side-products; they are part of an athlete's energy economy.

How common are gut problems in sport?

The honest answer is that prevalence estimates vary enormously depending on the sport, duration, intensity, heat and how symptoms are measured — published figures span roughly 4% to 96%. The pattern within that range, however, is consistent and useful.

Three risk factors fall out of the literature repeatedly: duration (symptoms escalate sharply beyond about two hours), modality (running provokes more symptoms than cycling, largely because of mechanical jostling), and ambient heat (higher temperatures markedly increase incidence). Roughly two hours at 60% of VO2max appears to be the threshold at which measurable gut perturbation appears, more or less regardless of training status.

Exercise-induced gastrointestinal syndrome explained

The umbrella term for what happens to the gut during hard, prolonged exercise is exercise-induced gastrointestinal syndrome (EIGS), formalised in a 2017 systematic review by Costa and colleagues. It is not one problem but four interacting ones.

Image: "Digestive system diagram" by Mariana Ruiz (LadyofHats), via Wikimedia Commons, public domain.

Splanchnic hypoperfusion — blood flow diverted away from the gut

During intense exercise, blood is redistributed to working muscle and skin. Gut blood flow can fall substantially. Reduced perfusion means reduced oxygen delivery to the intestinal epithelium, and those cells are metabolically demanding. Sustained ischaemia damages the tight junctions between them.

Increased intestinal permeability and endotoxaemia

Once tight junctions loosen, bacterial lipopolysaccharide can translocate into the bloodstream. The immune system responds with pro-inflammatory cytokines. In most athletes this is transient and self-limiting. In prolonged efforts in the heat, it can become clinically significant. Markers used in research include the lactulose:rhamnose ratio and intestinal fatty acid binding protein (I-FABP).

Delayed gastric emptying and carbohydrate malabsorption

The same stress that impairs the barrier also slows motility. Food and fluid sit in the stomach, producing fullness, nausea and the "sloshing" sensation athletes describe. Unabsorbed carbohydrate then draws water into the intestinal lumen osmotically and is fermented rapidly by colonic bacteria — producing gas, cramping and urgent, loose stools.

Neuroendocrine and gut–brain signalling

Sympathetic nervous system activation reduces gut motility and secretion. Pre-race anxiety adds to this via the gut–brain axis, which is why some athletes get symptoms on the start line before they have taken a single step. Practical work on the vagus nerve and the gut is relevant here.

The athlete microbiome: what the research shows

Image: "2020 UCI Road Cycling World Championships", via Wikimedia Commons, CC BY-SA 4.0.

Athletes appear to have more diverse gut microbiomes

The landmark study here is Clarke and colleagues' 2014 paper in Gut, which compared 40 elite male professional rugby players with two groups of sedentary male controls matched for age and body mass index. The athletes showed significantly greater alpha diversity, spanning 22 distinct phyla, alongside better metabolic and inflammatory markers. Diversity correlated with both protein intake and plasma creatine kinase.

That last detail is the important caveat. The athletes ate very differently from the controls, so the study cannot separate the effect of exercise from the effect of an athletic diet. The authors were explicit about this, and later reviews have reinforced it. High microbiome diversity is associated with health, but "associated with" is doing real work in that sentence.

Veillonella and the lactate–propionate pathway

The most widely reported finding in this field came from Scheiman and colleagues in Nature Medicine in 2019. Analysing stool from Boston Marathon runners, the team found the genus Veillonella increased in relative abundance after the race and was more abundant in runners than in sedentary controls. Veillonella uses lactate as its sole carbon source and converts it to propionate.

The researchers isolated Veillonella atypica from a runner and gave it to mice, which then ran approximately 13% longer to exhaustion on a treadmill than mice given a control organism unable to metabolise lactate. Delivering propionate directly into the colon reproduced the effect.

It is an elegant piece of work, and it is worth being precise about what it demonstrates: a plausible, mechanistically supported pathway shown in mice, arising from an observation in a small human cohort. It is not evidence that taking a Veillonella supplement will make you faster. That trial has not been done in humans.

Short-chain fatty acids and endurance

The broader and better-supported point is that fibre-fermenting bacteria produce short-chain fatty acids that feed the colonocytes, support barrier integrity and modulate inflammation. This is one of the few places where the microbiome literature and practical sports nutrition advice converge cleanly: eat more plants, more varied plants. See 30 plants a week and how to increase gut bacteria diversity.

Where the evidence currently ends

Most athlete microbiome studies are cross-sectional, small, and confounded by diet. There is no validated "athlete microbiome signature" you can test for and correct. Anyone selling you that certainty is ahead of the science. Our gut microbiome test UK guide and microbiome test comparison set out what these tests can and cannot tell you.

Common gut symptoms in athletes and what they mean

Tracking stool form across a training block is more informative than most athletes expect. The Bristol Stool Chart is a simple, validated way to do it. Persistent bloating between sessions may be a separate issue — see foods that cause bloating and best supplements for bloating.

Building a resilient gut in the training block

Image: CSIRO ScienceImage, "A selection of fruit and vegetables", via Wikimedia Commons, CC BY 3.0.

The single biggest mistake athletes make is treating gut health as a race-week problem. The gut you race with is the gut you built over the preceding months.

Fibre and plant diversity

UK guidance recommends 30 g of fibre daily for adults, and most people fall well short. For athletes, the goal is not only quantity but variety — different fibres feed different bacteria. Aim for a wide rotation of vegetables, fruit, wholegrains, legumes, nuts, seeds and herbs. Our guides to high fibre foods, how to increase fibre without bloating, prebiotic foods and resistant starch cover the practicalities.

Crucially, high fibre intake belongs in the base phase, not the 48 hours before a race. Deliberately dropping fibre in the final day or two is a legitimate, evidence-informed tactic — not a contradiction.

Fermented foods

Regular fermented food intake is one of the few dietary levers with reasonable evidence for increasing microbial diversity. Live yoghurt, kefir, sauerkraut, kimchi, miso and traditional cheeses all qualify. Introduce them gradually — a sudden jump can provoke exactly the bloating you are trying to avoid. See fermented foods UK, kefir benefits and fermented food vs probiotics.

Image: "Saurkraut" via Wikimedia Commons, CC BY-SA 3.0.

Polyphenols

Berries, cocoa, olive oil, green tea, coffee and coloured vegetables supply polyphenols, which act partly as microbial substrates. This is a low-risk, well-tolerated addition for most athletes — see polyphenols and gut health.

Protein: enough, but not crowding out plants

Athletes often push protein to 1.6–2.2 g/kg and, in doing so, displace fibre-rich foods. The Clarke rugby study found protein intake correlated with diversity, but that cohort was also eating a large total volume of food. If your protein intake is squeezing out vegetables and wholegrains, the net effect on your microbiome is likely negative.

A sample gut-supporting day in a training block

Training the gut: raising carbohydrate tolerance

Image: "Porridge oats" via Wikimedia Commons.

Why gut training works

The intestine's capacity to absorb carbohydrate is not fixed. Repeated exposure to carbohydrate during exercise upregulates the intestinal transporters involved — SGLT1 for glucose and GLUT5 for fructose — and improves gastric emptying and subjective comfort. Jeukendrup's review concluded that nutritional training can improve both emptying and absorption and reduce the likelihood and severity of GI problems. Costa's group has shown that two weeks of repetitive gut challenge during exercise reduces symptoms and malabsorption.

Understanding the carbohydrate ceiling

A single carbohydrate source saturates at roughly 60 g per hour because it relies on one transporter. Combining glucose and fructose recruits a second pathway. The 2016 American College of Sports Medicine position stand set the practical ceiling at up to 90 g/h from multiple transportable carbohydrates for events beyond about 2.5–3 hours.

Since then, the professional peloton has normalised 100–120 g/h. Research has followed, though not uniformly: Podlogar and colleagues showed that 120 g/h in a 0.8:1 fructose-to-glucose ratio increased exogenous carbohydrate oxidation compared with 90 g/h, but did not additionally spare endogenous glycogen. The reasonable summary for most athletes reading this is that 90–120 g/h represents the current evidence-based upper range, and that the higher end requires a gut that has been deliberately prepared for it.

A four-to-six week gut training progression

Practical rules for gut training

• Change one variable at a time — dose, product or ratio, never all three.
• Feed on a clock, not on feel. Every 15–20 minutes beats large boluses.
• Match fluid to carbohydrate concentration. A gel taken without water behaves like a hypertonic bolus.
• Score symptoms numerically after every session. Perception drifts; written records do not.
• Do not gut-train in a taper week. It belongs in the build.

Race day: a gut-friendly fuelling protocol

Image: US Navy photo by Journalist 1st Class Monica Darby, via Wikimedia Commons, public domain.

48 to 24 hours out

Carbohydrate loading is standard for events beyond about 90 minutes, typically 8–12 g/kg body mass per day. This is also the point to reduce fibre and high-FODMAP foods, which lowers residue in the colon and reduces fermentable substrate on race morning. Hydrate steadily rather than in large volumes.

The pre-race meal

Eat 3–4 hours before the start. Prioritise familiar, low-fibre, low-fat, moderate-protein carbohydrate: white toast with honey, plain porridge made with water, white rice, a sports drink. Avoid anything novel. A small top-up of 30–60 g carbohydrate in the final 60–90 minutes is reasonable if it has been rehearsed.

During the event

Heat, dehydration and anti-inflammatories

Three factors reliably worsen gut symptoms and are all partly within your control. Heat amplifies splanchnic hypoperfusion, so heat acclimation and cooling strategies have a gut benefit as well as a thermoregulatory one. Dehydration compounds the same problem. And non-steroidal anti-inflammatory drugs such as ibuprofen — still taken prophylactically by a surprising number of endurance athletes — increase intestinal permeability and gastric injury. This practice should be abandoned; see ibuprofen and stomach damage.

Recovery: repairing the gut after hard efforts

The hours after a hard session

Barrier disruption after prolonged exercise is generally transient. The practical priorities are rehydration with sodium-containing fluid, carbohydrate to restore glycogen, and 20–40 g of protein. Many athletes find that a liquid or semi-solid recovery feed is better tolerated in the first hour than solid food, particularly after a race.

If you have finished with significant symptoms, reintroduce fibre gradually over 24–48 hours rather than immediately returning to a high-fibre meal. Our guide on recovering after a stomach upset covers a similar staged approach.

Sleep, stress and the parasympathetic side of recovery

Digestion is a parasympathetic activity. Athletes who train hard, sleep badly and live with elevated psychological stress tend to accumulate gut symptoms independent of what they eat. There is a bidirectional relationship here — poor sleep worsens gut symptoms and gut symptoms worsen sleep. See gut health and sleep.

Travel and competition abroad

Travel disrupts routine, water source, food supply and circadian rhythm simultaneously. Plan familiar foods, be conservative with local water and raw foods in higher-risk destinations, and consider prophylactic strategies discussed in travel probiotics and probiotics for traveller's diarrhoea. Athletes working night shifts around training should read shift work and digestion.

Low FODMAP for athletes: when and how

What the evidence shows

FODMAPs are fermentable short-chain carbohydrates. In irritable bowel syndrome, restricting them is well established. In athletes, the evidence is smaller but consistent in direction.

Lis and colleagues randomised 11 recreationally competitive runners with a history of exercise-associated GI symptoms to six days of low-FODMAP or high-FODMAP diet in a single-blinded crossover. Daily GI symptom burden was significantly lower on the low-FODMAP diet, with reductions in flatulence, urge to defecate, loose stool and diarrhoea. Symptoms during exercise did not differ significantly. A separate crossover in 16 recreational runners found that a seven-day low-FODMAP diet reduced exercise-related GI symptoms and improved perceived ability to exercise.

Two things follow. First, this is a real and useful tool. Second, the strongest signal is for daily symptoms in the training block and the days before competition — not necessarily for symptoms mid-race.

How to use it safely

1. Restriction (2–4 weeks maximum). Not indefinitely. Prolonged restriction reduces fermentable substrate and can lower beneficial bacteria including bifidobacteria.
2. Reintroduction. Systematically challenge each FODMAP group to identify your personal triggers. See FODMAP reintroduction.
3. Personalisation. Build the least restrictive long-term diet that controls symptoms.

This is best done with a registered dietitian, particularly for athletes, where energy availability and micronutrient intake are already under pressure. Start with the low FODMAP diet UK guide and the FODMAP food list. If symptoms look more like a chronic functional disorder, review IBS types and supplements for IBS.

Supplements: what the evidence supports

Supplements sit downstream of diet, sleep, load management and gut training. With that stated plainly, several have credible evidence.

Probiotics

The most directly relevant athlete trial is Pugh and colleagues' 2019 study. Twenty-four recreational runners took either a multi-strain probiotic (25 billion CFU of Lactobacillus acidophilus CUL60 and CUL21, Bifidobacterium bifidum CUL20 and Bifidobacterium animalis subsp. lactis CUL34) or placebo for 28 days before a marathon. Moderate GI symptoms fell in the third and fourth weeks of supplementation in the probiotic group but not placebo. During the race, lower symptom severity was associated with better pace maintenance: the placebo group slowed by 14.2% from the first to the last third of the race versus 7.9% in the probiotic group. Finish times did not differ significantly, and markers of permeability were unchanged between groups.

A separate three-month randomised trial in long-distance runners found reduced constipation and subjective health improvement with a multi-strain probiotic.

Practical takeaways: strains matter, dose matters, and the effect takes weeks. Start at least four weeks before a target event, never on race week. Browse the Welzo probiotics range and read best probiotics UK, how to choose a probiotic, when to take probiotics and how long probiotics take to work.

Prebiotics and fibre supplements

Useful in the base phase, counterproductive close to competition. Partially hydrolysed guar gum and psyllium are generally better tolerated than inulin at higher doses. See best prebiotic supplement UK and psyllium vs inulin.

Barrier-support supplements

Anti-doping: a non-negotiable for competing athletes

Any athlete subject to testing should only use supplements batch-tested under a recognised programme such as Informed Sport. Contamination of unregulated products is a documented and career-ending risk. Also review probiotic side effects and probiotic safety, particularly if you are immunocompromised.

Testing and when to see a doctor

Red flags that need medical assessment

• Blood in the stool, or black tarry stools
• Unintentional weight loss
• Persistent vomiting or difficulty swallowing
• Symptoms that wake you from sleep
• A change in bowel habit lasting more than six weeks, especially over the age of 50
• Iron deficiency anaemia without an obvious cause
• A family history of bowel cancer, coeliac disease or inflammatory bowel disease

These are not "train through it" symptoms. See when to see a GP about stomach symptoms.

Tests that may be appropriate

Depending on the clinical picture, a clinician may consider coeliac serology, faecal calprotectin to distinguish inflammatory from functional disease, Helicobacter pylori testing, full blood count and ferritin, and in selected cases breath testing. Relevant guides: coeliac testing, calprotectin testing, SIBO testing and gut health blood tests.

Special considerations by athlete group

Female athletes

Gut transit and symptom sensitivity vary across the menstrual cycle, with many athletes reporting looser stools and greater bloating around menstruation. Tracking symptoms alongside cycle phase often explains variability that otherwise looks random. See gut health and hormones, best probiotics for women and, for masters athletes, gut health in menopause.

Masters athletes

Microbial diversity tends to decline with age, and medication use rises. Long-term proton pump inhibitors and metformin both alter the gut environment — see omeprazole long-term effects and gut health in older adults.

Vegan and plant-based athletes

Usually excellent fibre diversity, but high habitual fibre and FODMAP load can create its own problems around competition. Vitamin B12, iron and omega-3 need attention. See vegan gut health and vegan probiotics.

After a course of antibiotics

Athletes are not exempt from the microbiome disruption antibiotics cause. Plan a deliberate rebuilding phase rather than assuming recovery is automatic — see probiotics after antibiotics and Saccharomyces boulardii.

An eight-week gut plan for athletes

For a broader reset outside of a competitive block, see our gut reset protocol and best foods for gut health.

Frequently asked questions

What is the best way to improve gut health for athletes?

Build the foundation first: 30 g of fibre daily from a wide variety of plants, regular fermented foods, adequate sleep and sensible training load management. Then add sport-specific work — deliberate gut training to raise carbohydrate tolerance, a rehearsed race-day fuelling plan, and reduced fibre in the final 24–48 hours before competition. Supplements such as a multi-strain probiotic are a useful addition, not a substitute, and need at least four weeks to show an effect.

Why do runners get diarrhoea during long runs?

"Runner's trots" result from several mechanisms acting together: blood flow is diverted away from the gut, transit accelerates, unabsorbed carbohydrate draws water into the intestine osmotically, and the mechanical impact of running jostles the bowel. Heat, dehydration and anti-inflammatory drugs all make it worse. Cycling produces fewer symptoms than running at equivalent intensity, which supports the mechanical component.

Do probiotics actually help athletes?

There is reasonable evidence for reducing gastrointestinal symptoms rather than directly improving performance. In a randomised trial of 24 marathon runners, a multi-strain probiotic taken for 28 days reduced symptom prevalence in the later supplementation weeks, and runners taking it slowed less over the final third of the race than those on placebo — although finish times did not differ significantly. Strain, dose and duration all matter, and effects build over weeks.

How long does it take to train your gut?

Plan for four to six weeks of progressive carbohydrate intake during one or two long sessions per week. Research showing reduced symptoms and malabsorption has used repetitive gut-challenge protocols over as little as two weeks, but most athletes moving from 60 g/h toward 90–120 g/h need longer. Never attempt this during a taper.

How much carbohydrate can an athlete absorb per hour?

A single carbohydrate source saturates at roughly 60 g/h. Combining glucose and fructose recruits a second transporter and allows higher rates. The established guideline is up to 90 g/h for events beyond 2.5–3 hours, with current evidence supporting a 90–120 g/h range for well-trained, gut-trained athletes. Higher intakes reliably increase exogenous carbohydrate oxidation, but the additional performance benefit above 90 g/h is not yet firmly established.

Should athletes follow a low FODMAP diet?

Only as a short, structured trial if daily gastrointestinal symptoms persist despite good basic nutrition. Two crossover studies in runners found reduced daily symptoms and improved perceived ability to exercise on short-term low-FODMAP diets. Restriction should last two to four weeks at most, followed by systematic reintroduction, ideally with a registered dietitian, because prolonged restriction reduces fermentable fibre and can lower beneficial bacteria.

Do athletes have different gut bacteria from non-athletes?

They appear to. A study of 40 elite rugby players found significantly greater microbial diversity across 22 phyla compared with matched sedentary controls, alongside better metabolic markers. Research in marathon runners identified higher levels of Veillonella, a genus that converts lactate to propionate. However, athletes also eat very differently, so diet and exercise cannot be fully separated in these studies.

Can gut problems affect athletic performance?

Yes, through two routes. Directly, symptoms limit how much fuel and fluid you can take in, which impairs performance in events lasting more than two hours. Indirectly, impaired barrier function during prolonged exercise in the heat allows bacterial fragments into circulation, contributing to inflammation and, in severe cases, to exertional heat illness. There is also evidence that runners with fewer symptoms maintain pace better in the closing stages of a marathon.

What should I eat before a race to avoid stomach problems?

Eat a familiar, low-fibre, low-fat, carbohydrate-based meal three to four hours before the start — white toast with honey, plain porridge made with water, or white rice all work well. Reduce fibre and high-FODMAP foods for the preceding 24 to 48 hours. A 30–60 g carbohydrate top-up in the final hour is reasonable if rehearsed. Never introduce a new food or product on race day.

When should an athlete see a doctor about gut symptoms?

Seek medical assessment for blood in the stool, black tarry stools, unintentional weight loss, persistent vomiting, difficulty swallowing, symptoms that wake you at night, iron deficiency anaemia without clear cause, or any change in bowel habit lasting more than six weeks — particularly over the age of 50 or with a family history of bowel cancer, coeliac disease or inflammatory bowel disease. These require investigation rather than dietary self-management.

References

1. Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome — implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics. 2017;46(3):246–265. View study
2. Scheiman J, Luber JM, Chavkin TA, et al. Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism. Nature Medicine. 2019;25:1104–1109. View study
3. Clarke SF, Murphy EF, O'Sullivan O, et al. Exercise and associated dietary extremes impact on gut microbial diversity. Gut. 2014;63(12):1913–1920. View study
4. Jeukendrup AE. Training the gut for athletes. Sports Medicine. 2017;47(Suppl 1):101–110. View study
5. Pugh JN, Sparks AS, Doran DA, et al. Four weeks of probiotic supplementation reduces GI symptoms during a marathon race. European Journal of Applied Physiology. 2019;119:1491–1501. View study
6. Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK. Low FODMAP: a preliminary strategy to reduce gastrointestinal distress in athletes. Medicine & Science in Sports & Exercise. 2018;50(1):116–123. View study
7. Wiffin M, Smith L, Antonio J, Johnstone J, Beasley L, Roberts J. Effect of a short-term low FODMAP diet on exercise-related gastrointestinal symptoms. Journal of the International Society of Sports Nutrition. 2019;16:1. View study
8. Podlogar T, Bokal Š, Cirnski S, Wallis GA. Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g/h versus 90 g/h. European Journal of Applied Physiology. 2022;122:2393–2401. View study
9. Costa RJS, Young P, Gill SK, et al. Assessment of exercise-associated gastrointestinal perturbations in research and practical settings. International Journal of Sport Nutrition and Exercise Metabolism. 2022;32(5):387–418. View study
10. Mohr AE, Jäger R, Carpenter KC, et al. The athletic gut microbiota. Journal of the International Society of Sports Nutrition. 2020;17:24. View study
11. Smarkusz-Zarzecka J, Ostrowska L, Leszczyńska J, Cwalina U. Effect of a multi-strain probiotic supplement on gastrointestinal symptoms and serum biochemical parameters of long-distance runners. International Journal of Environmental Research and Public Health. 2022;19(15):9363. View study
12. Close GL, Morton JP, et al. Dietary carbohydrate and the endurance athlete: contemporary perspectives. Gatorade Sports Science Institute — Sports Science Exchange. Read article
13. Editorial: Nutrition to support gut health and the microbiome in athletes. Frontiers in Nutrition. 2023. Read article
14. National Institute for Health and Care Excellence. Irritable bowel syndrome in adults: diagnosis and management (NG61). View guideline
15. NHS. Irritable bowel syndrome (IBS). View NHS guidance
16. British Dietetic Association. Fibre — Food Fact Sheet. View resource
17. Informed Sport. Batch-tested supplement certification for athletes. Visit site

About the author

Dr Zeeshan Afzal, MBBS is a practising doctor and Medical Content Lead at Welzo. He writes and medically reviews Welzo's digestive health content, with a focus on translating peer-reviewed gastroenterology and sports nutrition research into practical guidance for UK readers.

Medical disclaimer

This article is for general information and education only. It is not a substitute for individual medical advice, diagnosis or treatment from a qualified healthcare professional. Do not delay seeking medical advice because of something you have read here. If you experience blood in your stool, unexplained weight loss, persistent vomiting, or a change in bowel habit lasting more than six weeks, contact your GP. In an emergency, call 999 or attend your nearest A&E. Supplements are not intended to diagnose, treat, cure or prevent any disease, and competing athletes should only use batch-tested products.

Continue reading

• Runner's trots: causes and how to stop them
• Gut health in the UK: the complete guide
• Best probiotics UK
• The low FODMAP diet UK guide
• Gut dysbiosis explained
• Do probiotics actually work?