Why you should improve your gut health to run better

It’s the day of your big race. You’ve done the training and you’re toeing the line injury-free. Things go well for the first few miles, but then the rumblings begin. Your stomach begins to gurgle, bloat and cramp. You try hard to run through it, but there’s no escape – you’re forced to divert to a portable loo, or to stop by the side of the road. It happens to the best. Paula Radcliffe was caught short at the London Marathon in 2005 and similar emergencies have taken down runners before and since.

‘There is evidence to suggest that the incidence of gastrointestinal distress is higher among runners than in athletes from sports with less mechanical trauma, such as cycling or swimming,’ says Nathan Lewis, senior performance nutritionist at the English Institute of Sport. In one study, published in the Scandinavian Journal of Gastroenterology, 45 per cent of runners reported suffering from gastrointestinal (GI) symptoms, such as cramping, bloating, reflux, nausea, vomiting and diarrhoea.

It’s little wonder. Aside from the jarring action of running, oxygenated blood flow to the gut is reduced by as much as 80 per cent, as it’s diverted to the working muscles and skin for heat dissipation. ‘This can result in an inadequate supply of oxygen and nutrients to the gut mucosa – the innermost layer of the gastrointestinal tract – which gut-related problems,’ explains Lewis. ‘For example, increased permeability of the gut barrier, allowing bacterial components into the bloodstream, where they invoke an inflammatory response.’ This manifests itself in classic GI symptoms, including nausea, tummy ache, cramps and urgency.

Such symptoms can ruin your race as surely as a twisted ankle will. But is gut distress simply an inevitable hazard of our sport? Not necessarily. While there’s no one-size-fits-all solution, there are plenty of strategies to try to help you get to the bottom of the problem (pun intended).

What’s more, taking care of your gut for the sake of your running may also have a knock-on beneficial effect on your overall wellbeing. The health of your gut microbiome (the population of microbes in your digestive tract) has been shown to influence the immune system, neural function, mental health and body weight. One study, published in the Journal of Proteome Research, suggested a lack of bacteria in the large intestine could cause obesity by slowing down the activity of ‘brown’ fat, which protects against weight gain. In fact, so great is the gut’s influence that it’s been called the ‘second brain’.

This second brain is composed of tens of trillions of microbes from more than 1,000 different species or strains. But, says Professor Tim Spector, Professor of Genetic Epidemiology at King's College London and author of The Diet Myth: The Real Science Behind What We Eat, every individual’s microbiome is as unique as a fingerprint. ‘That’s one of the reasons why people don’t respond the same way to different diets or exercise regimes,’ he says.

But the good news from emerging research is that exercise appears to have a positive effect on the gut microbiome. ‘Evidence from rat studies is strongly suggestive that running alters microbe composition to favour chemicals called short chain fatty acids [SCFAs],’ says Spector. ‘These strengthen immunity, dampen inflammation and prevent leaky gut, in which microbes and toxins cross between the gut and the blood. There is sparse human data, but twin studies show a good correlation between regular exercise and a healthy microbiome.’

One of the main definitions of ‘healthier’ when it comes to gut microbes is ‘diverse’. ‘The more species you have, the more vitamins and metabolites they are producing,’ says Spector. ‘While many vitamins come from the food we eat, our gut microbes also produce them.’ And studies have shown that gut microbes, in particular, aid the production of vitamin K and the B vitamins. It’s one of the reasons Spector is sceptical about the current trend for eliminating food groups – such as wheat or dairy – to solve dietary issues. ‘The less varied the diet, the more it reduces diversity in the gut microbiome – in the long term you’re going to pay a price,’ he says. Infant studies have shown that the less diverse the microbiome at three months, the more likely the chances of developing food allergies later on.

But that doesn’t mean you can’t make changes to your diet to reduce your chances of suffering from GI symptoms when training and racing. Lewis has worked with diarrhoea-prone elite athletes and says dietary alterations in the 48 hours before a race can solve the problem. ‘I recommend temporarily removing high-fibre foods, like vegetables, pulses, nuts and beans, from the diet. Stick to easy-to-digest foods, basing meals around white rice, potatoes without the skins, or porridge oats in the morning. This leaves you with little fibrous bulk in the large bowel by race morning.’

That said, there is wide variation in the foods that, consumed too close to physical exertion, cause a gut reaction. ‘Dairy isn’t great for some athletes because the proteins it contains can clot in the stomach,’ says Lewis. ‘And, anecdotally, some people report improvements in symptoms when they avoid gluten.’

As these issues vary so much from person to person, keeping a detailed food and symptom diary can be helpful in identifying your personal triggers. You can download one free of charge from the World Gastroenterology website. ‘If you identify a potential food or type of food, I’d advise cutting portion size initially – this can make a huge difference,’ says Lewis. Perhaps you can’t tolerate a pile of lentils but you’re fine with a small helping.’

Timing is also important. ‘For those prone to diarrhoea, I would recommend eating four hours before a race, opting for something low in fat and free of fibre,’ says Lewis. ‘But you need to experiment to see what works for you.’

For training sessions of under an hour, avoiding food altogether beforehand might be the solution. ‘Eating itself increases peristalsis [contractions that move food] in the gut,’ says Lewis. ‘As long as you have a decent-sized meal the evening before, you’ll have enough fuel for training of this duration. And just swilling the mouth with a carb drink has been shown to have a positive effect on performance.’

Hydration is also an important factor in avoiding or reducing GI symptoms. ‘Getting your fluid status right is essential,’ says Lewis. Exercising in a hypo-hydrated state (under-hydrated, though not necessarily dehydrated) affects the rate at which the stomach empties, which could trigger problems. It’s best to avoid starting exercise in a dehydrated state rather than attempting to down lots of fluid on the run. An excessive volume of fluid, along with the air you take in while drinking, has been shown to increase stomach discomfort.

It’s also a good idea to look at your fuelling strategy. ‘Have you used the same carb drink or gel in training that you’re going to use in racing?’ says Lewis. ‘Do you take caffeine before or during races for performance benefits that you have not been using in training?’

Many sports nutrition products – especially gels – now contain a mix of glucose and fructose. Since these two sugars have different ‘transporters’ into the bloodstream, this enables you to maximise your carb intake on the run. However, says Lewis, too much fructose can cause diarrhoea because it draws water into the gut. Research has shown that the benefit of dual or multi-source carbs only overtakes simple glucose or maltodextrin when you’re consuming more than 60g of carb per hour. So, if you’re taking in less than this, there’s no need to use a product that contains fructose and risk upsetting your stomach. Be mindful of what you drink in the hours prior to running, too: a large glass of fructose-rich apple juice or a fruit smoothie could cause GI problems on the run.

One much-touted measure for improved gut health is to increase your intake of probiotics, either through supplementation or diet. Probiotics are microorganisms that benefit human health, and they can help to restore a healthy microbiome that’s been thrown off by illness, medication (especially antibiotics), foreign travel, stress or poor diet. Studies have shown that probiotics can improve intestinal barrier integrity in those suffering from acute illness, reducing GI symptoms such as cramps, bloating and diarrhoea, but this hasn’t been shown specifically in exercisers. Still, The English Institute of Sport is recommending that Team GB athletes take probiotics, based on a growing body of research backing up their beneficial effect on the athletes’ health.

For example, an Australian study found that fatigue-prone athletes were lacking in interferon, a protein that helps regulate the immune system. They were given probiotics daily for a month and the deficit was corrected. And research published in the International Journal of Sport Nutrition and Exercise Metabolism found a reduction in upper respiratory tract infections and post-marathon GI symptoms with probiotic use.

While there is no direct evidence in humans of a physical performance benefit, a recent study in the Journal of Strength and Conditioning Research found that mice stripped of their gut bacteria performed worse in a swimming-endurance task than those with a healthy gut microbiome. Spector, however, believes more evidence is needed before recommending ‘blanket use’ of probiotic supplements, instead recommending that people look to dietary probiotic sources. ‘I’d rather people ate a natural yoghurt,’ he says. Other foods that are high in probiotics include fermented foods such as kimchi, miso, kefir and sauerkraut.

Spector also points out that probiotic supplements aren’t all created equal and there is little regulation regarding what they should contain, or whether they even contain what they say they do. ‘You need a product that contains a minimum of five billion bacteria [per capsule] to ensure enough reaches your colon,’ he says. ‘Check the label. You also want a range of species – many products only contain a couple of strains of bacteria.’ Try Monkey MX Digestive Enzymes, which boosts your existing supply of digestive enzymes, BioCare FOS powder prebiotic supplement or HealthSpan High-strength Probiotic, which comes recommended by The English Institute of Sport.

Also, be aware that the benefits of taking probiotics last only as long as you continue to take them. ‘They are like tourists,’ says Spector. ‘They only benefit the health of the local economy for the fortnight they are there.’ So it’s key that you keep your intake consistent if you want to reap the benefits.

Other foods that sustain useful microbes in the gut include those rich in polyphenols, such as olive oil, nuts and seeds, green tea, coffee and dark chocolate. Polyphenols encourage some microbes, such as lactobacilli, to flourish and also prevent unwanted microbes from colonising the guts.

The importance of prebiotics is also becoming increasingly apparent. ‘Prebiotics are like fertilisers for your gut microbes, encouraging the good species to grow,’ explains Spector. They can’t be digested in the upper part of the digestive tract so they reach the colon, where they are ‘digested’ by the microbiome. Prebiotics come in the form of starches in the diet, including oligosaccharides, oligofructose and inulin. ‘There’s evidence that a high-prebiotic diet can improve the health of the microbiome,’ says Spector.

However, they can also cause gas and bloating. ‘This is why portion size is so crucial,’ says Lewis. ‘Many people can tolerate small amounts of prebiotic-rich foods, but will experience significant bloating, wind or diarrhoea if they go beyond a certain quantity.’ Many of the key prebiotic foods are the same ones that IBS [Irritable Bowel Syndrome] sufferers following the low-‘FODMAP’ diet are told to avoid. FODMAP stands for Fermentable, Oligo-, Di- and Mono-saccharides and Polyols – some of the ‘culprit’ foods are wheat, garlic, dried fruit, kidney beans, milk, cabbage, onions, apples and cherries.

‘Athletes with a history of IBS may benefit from trying the low-FODMAP diet, with assistance from a health professional,’ says Lewis. ‘Reducing the exposure of the gut to certain fermentable carbs (fructo-oligosaccharides and galacto-oligosaccharides) could resolve their symptoms altogether.’ But Spector points out that it could be just one or two specific foods from the FODMAP family causing the problem. ‘Runners with IBS need to experiment to see which foods give them problems and which are fine,’ he says. ‘The long-term goal is maximum diversity and sufficient fibre.’

Dr Sepp Fegerl, medical director at Viva Mayr, a clinic specialising in digestive health, believes that it’s not just what we eat, but also how we eat that can affect our gut happiness. ‘Digestion begins in the mouth,’ he says. ‘That’s why chewing your food properly is so essential. The action of chewing, combined with the liquid and enzymes contained in saliva, breaks the food down, giving the maximum number of nerve endings in the tongue information to send to the brain about what the food is. The more liquid and the longer in the mouth, the more detailed the information sent to the intestinal organs on how to respond. This leads to optimal digestion and absorption of the nutrients.’ Fegerl recommends chewing every mouthful 30-40 times. This also slows down the rate at which you eat.

At Viva Mayr, the guests are encouraged to eat alone, without distractions. ‘We recommend not drinking anything with your meals, but especially no iced or carbonated drinks,’ says Fegerl. ‘Also, avoid drinking half an hour before eating and an hour after. Fluid dilutes digestive liquids and affects transit time, leading to reduced absorption of nutrients.’

If you feel as if you’ve tried everything and aren’t getting any relief from your gut discomfort, it’s worth getting a check-up to rule out any serious problems within your digestive tract. Lewis says you could then consider trying the FODMAP diet, or an elimination diet, in which you strip the diet right back, wait for symptoms to disappear and then reintroduce suspect foods one by one to see if you get a reaction. But he cautions against doing this alone. ‘Work with a dietitian or nutritionist or you risk an unbalanced diet that could cause your performance – and health – to suffer,’ he says. ‘For example, eliminating dairy can be a big risk for endurance athletes – potentially compromising their calcium intake and bone health.’

Also, take comfort from the fact that, when it comes to running-related gut health, time is a great healer. ‘GI symptoms tend to lessen over time,’ says Lewis. Novice runners tend to suffer more than experienced runners, and younger runners more than older runners.’

Spector’s final piece of advice is something that we runners are frequently encouraged to do: ‘Listen to your body,’ he says. ‘Experiment, but aim for diversity and eat ‘real’ food wherever possible.’ It’s a simple message to take away, but for both your running and your all-round health, it’s a recipe for success.


Photography by Agata Pec. Styling by Emma Ritchie Calder.