How gut health affects cycling performance

Vicky Ware examines how our personal bacterial culture has more of a hand in our physical and mental sporting performance than sports scientists first thought

Your body is playing host to a huge ecosystem. There are trillions upon trillions of bacteria that call your skin, mouth and intestines home. Your intestines house the most microorganisms with nearly 2kg of bacterial mass, but saving weight here won’t make you faster on the bike. The microbes on your body are collectively known as the microbiome, and scientists are just unravelling the huge impact this ecosystem is having on our health. Everyone has a unique microbial fingerprint made up of different species of bacteria. Which species you have impacts on your health — and potentially your sporting performance.

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The types of bacteria in your microbiome are affected by your diet, genetics and which bacteria you come into contact with on a daily basis. Your adult microbiome is even affected by things that happened to you in childhood; whether you were born by caesarean section or naturally, breast or bottle fed and even what your mum ate while she was pregnant.

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Some experts believe that western lifestyles are leading to ‘dysbiosis’ — a promotion of the wrong kinds of bacteria in our gut, due to stress, diet and increased hygiene. With this has come a plague of disease based on chronic inflammation, from cancer to asthma and allergies.

Sporting impact

There’s also evidence that these microbial hitch-hikers are affecting sporting performance. A study by Hsu and colleagues at the Graduate Institute of Sports Science in Taiwan found that mice bred in a sterile environment (known as germ-free mice) have a poor exercise performance ability compared to mice bred with normal bacterial populations. Mice bred with exposure to only one kind of bacteria were better at exercise than germ-free mice, but not as good as those with diverse microbial populations.

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The researchers theorise this may be due to the increased antioxidant capacity of mice with a microbiome. Intense exercise produces large amounts of free radicals that need to be mopped up by antioxidant enzymes to stop them causing damage to cellular components, such as DNA and proteins — the opposite of recovery. The microbiome increases the body’s ability to mop up free radicals, enhancing the ability to recover from exercise.

Professor Tim Spector, founder of the British Gut Project and author of The Diet Myth, thinks it likely that the microbiome is impacting on sporting performance. “One study of the Irish rugby team did find they had more healthy and diverse microbes but more human studies are needed,” he explains. Fellow microbiome researcher and author of Follow Your Gut, Rob Knight agrees that the bacteria are probably impacting your cycling ability. “But there is little data in humans to support this yet,” he says.

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Another reason for cyclists to consider their microbiome is when using beetroot juice to improve performance. Studies have shown that people who use antibacterial mouthwash completely remove the benefits of consuming beetroot juice, which is beneficial because of its inorganic nitrates that are precursors to nitric oxide, the compound that actually enhances exercise ability. It turns out the bacteria in your mouth are essential to begin the process of breaking inorganic nitrates down to nitric oxide.

Another way your microbiome could be impacting on your performance on the bike is through weight gain. Researchers first noticed the microbiome may affect obesity when a slim person given a faecal transplant (that’s exactly what you think it is) from an overweight person became overweight themselves.

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Faecal transplants are now an accepted treatment for infection with clostridium difficile — which causes diarrhoea and is difficult to get rid of any other way. The fact that a faecal transplant is used rather than transferring specific species of bacteria shows that experts are not yet sure which bacteria are beneficial, or whether it’s a combination of bacterial species.

Studies are also beginning to show how the microbiome impacts mental health. Experts are in the early stages of understanding how the relationship between gut and brain works, but it’s an exciting prospect for sports performance.

For example, germ-free mice seem to show more risk-taking behaviour than mice with a normal microbiome, and be less anxious. Other studies have shown transferring the microbiome of an anxious mouse to a non-anxious one transfers the anxiety. Is it possible that the bacteria in your gut fuel your adrenaline-junkie love of racing down mountains? We’re only just beginning to find out.


Own recovery drink for healthy gut bacteria

Making your own recovery drinks can help maintain healthy gut bacteria

As a cyclist, you may eat more refined carbohydrates than would normally be the case in a healthy diet. Eating them while exercising doesn’t stop this impacting on your gut bacteria, which can only eat what you eat. Different species of bacteria eat different things — it’s survival of the fittest, and your diet determines which bacteria are capable of surviving.

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Feeding a mouse a diet typical of people in western countries (high in sugar and certain types of fat) leads to changes in the type of bacteria in its gut compared to a non-western diet (higher in fibre and ‘good’ fats) and to the mouse getting fat. Transfer of these bacteria to a different mouse leads to that mouse getting fat almost regardless of what it eats, suggesting the bacteria are leading to the weight gain not just the food.

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Sweeteners are not the answer to cutting down sugar in your diet when it comes to a healthy microbiome. Sucralose, aspartame and saccharin reduce bacterial diversity, meaning fewer species of bacteria are in your gut. They also seem to change the kind of bacteria that can live there, leading to altered metabolism and potentially even obesity and diabetes. Sweeteners are often found in sports foods, especially recovery protein powders. One option to reduce your intake is by making your own recovery powders from pure whey or pea protein mixed with the electrolytes and even probiotics of your choice.

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Professor Knight thinks other lifestyle factors are also impacting on the microbiome. He lists “lack of sleep, lack of exercise, allowing chronic inflammation to exist [e.g. via a food allergy or chronic stress], having a diet very high in meat or cheese or a diet without diverse kinds of plants” are all factors that could lead to a microbiome that isn’t helping your health. Others that don’t help, adds Spector, include “chronic lack of fibre from any source and overuse of antibiotics and junk food”. A diet high in diverse kinds of plants feeds a diverse range of bacteria, which is associated with a healthy immune system.

Immune health

The immune system not only stops upper respiratory tract infections (URTIs) that could prevent you from riding your bike, but repairs damaged muscle after hard training. Athletes are more susceptible to URTIs because intense exercise leads to a dip in the immune system’s ability to fight infection, allowing a window of opportunity for viruses and ‘bad’ bacteria.

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Probiotics have been shown to improve immune function, specifically through enhancing an athlete’s ability to recover and thereby reducing fatigue and preventing URTIs. Athletes taking probiotics are less likely to get an URTI in the first place — and when they do, they are both less severe and shorter in duration.

Since 2010 companies selling probiotics are not allowed to claim that they “boost the immune system” after the European Food Safety Authority ruled that these claims were unproven. This isn’t because probiotics were proven to have no impact on the immune system, but rather that the impact was so complicated that using a vague term like ‘boost’ wasn’t appropriate.

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The bacteria in your gut are also responsible for keeping the intestinal wall strong and in doing so maintaining a good barrier between what’s in your guts and the rest of your body. They say good fences make good neighbours, and this is true of your gut bacteria. While they’re promoting your health in the intestines, a breach in the barrier could allow opportunistic pathogens to infect your body.

A ‘leaky gut’ can also allow larger particles of food into your blood stream that can have a negative impact on health, promote inflammation, and potentially even autoimmune disease. Studies have shown that athletes are more likely to suffer from a leaky gut than non-athletes, and that probiotics can both help prevent and repair a leaky gut in these individuals.


A study at the University of Tasmania also found that athletes who use probiotics are able to keep exercising for longer in hot weather. After four weeks of consuming a probiotic supplement, containing lactobacillus, bifidobacterium and streptococcus, people were able to continue exercising for longer in 35°C.

Despite core temperature being the same whether people had taken a probiotic or not, they were able to keep running for longer when they had topped up their intestinal flora. More research is needed to find out exactly why probiotics have this effect.

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Athletes also need to eat more than non-athletes and this increase in food can have an impact on the health of your gastrointestinal tract, especially when the foods consumed are refined sugar-containing products like energy drinks and bars. Happily, probiotics have been shown to improve people’s ability to digest food. One study has even shown that probiotics can help maintain healthy GI tract function in athletes.

Topping up the flora

If you’re considering adding probiotics to your diet, either through foods that contain them or in tablet form, it’s worth adding a little at a time. Going from zero to hero when topping up your gut bacteria could lead to an upset stomach as your microbial ecosystem is thrown into disarray. Building up slowly should prevent any need to rush to the bathroom. Lactobacilli and bifidobacterium are two species that are almost certainly ‘good bacteria’, so if you’re going to go for a probiotic, these might be the ones to try.

Fermented foods naturally contain bacteria that were used in their creation and can be used to maintain your microbiome. These include kefir, sauerkraut, kombucha tea, miso soup and probiotic-containing yoghurts.

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One definite no-no when it comes to your microbiome is taking antibiotics when not absolutely necessary. They impact on your ‘good’ bacteria along with the one causing the problem, and seem to have a long-term effect on the diversity of bacteria in your microbiome. Research has shown that antibiotics have a long-term impact on levels of bifidobacterium in the gut.

Other studies have shown that the ratio of bifidobacterium to firmicutes in the gut is predictive of whether someone is lean or overweight, more firmicutes and you’re more likely to gain weight, suggesting antibiotics could lead to weight gain. Children given antibiotics are also more likely to develop asthma and allergies.

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While experts aren’t yet sure which bacteria are doing what when it comes to their impact on human health, or whether there even is a one-size-fits-all microbial milieu, it’s certainly exciting to consider the paradigm shift in thinking that has come from completed studies on the microbiome. If transferring bacteria from one person’s gut to another can transfer traits such as anxiety, could it also transfer sporting ability? If so Chris Froome and Bradley Wiggins may be sitting, quite literally, on a gold mine.

Which bacteria are best though?

Professor Knight explains: “It probably depends on who you are: different people have very different bacteria. Through projects like American Gut (and now British Gut) we’re just starting to find out why these differences exist and their effects on health.” Although he adds: “Bacteria that produce butyrate and a diverse population of bacteria are correlated with health.”

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Eating prebiotic foods — those which promote growth of good bacteria — can help the butyrate-producing bacteria in your gut. Soluble fibre is a key prebiotic. When broken down by bacteria, short-chain fatty acids (SCFA) are produced. Butyrate is an SCFA thought to be good for health by providing energy for the cells making up the intestinal wall and thereby decreasing leaky gut.

Polyphenol-containing foods are also important prebiotics. Professor Spector explains: “If you want to stay healthy eat a diverse range of real foods with high fibre and plenty of polyphenols, like olive oil and dark chocolate.”

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