The role of the gut bacteria in our bodies – known as the microbiome – has been a hot topic in medical research for a while. Given the impact that our microbiome has been found to have on digestive health, immunity, energy production, ability to lose weight and even the way in which our brain functions, it has not been surprising to see sports scientists starting to examine the role of gut bacteria on athletic performance.

For this blog, I have asked sports medicine doctor Nicky Keay ( to explain more about the microbiome and its potential links with performance. At the end, I’ve given some tips on how you can promote a healthy microbiome through diet and, when necessary, supplementation.

Role of the microbiome in health and performance

Our body acts as a host to vast array of micro-organisms. Often, we are only aware of these micro-organisms causing unwanted infection: for example, when a cut on the skin becomes infected, or we suffer with a bout of infective gastro-intestinal upset. This perception of the micro-organisms, living both on and inside us, only causing unwanted infections is very biased. In fact, the microbiome (all the micro-organisms, their genetic material and metabolites produced) plays a vital role in keeping us healthy.

Picture of gut bacteria

The gut microbiota consist of the range of micro-organisms living in our gut, mainly the colon. Recent research reveals that the diversity and functions of the gut microbiota have far reaching impact on health. For example, there is an important interaction between these micro-organisms and mitochondria, which are the organelles in cells responsible for producing energy. This cross talk is relevant for athletes who seek to optimise energy production for training and competition. The gut microbiota also interacts with the immune system and central nervous system function, including behaviour. There is evidence that the gut microbiota even influences brain development.

On the other side of the coin, any disruption in the beneficial types of gut microbiota have been linked to chronic disease states including obesity, metabolic syndrome and mental health issues. What causes imbalances in gut microbiota? Possible explanations include a poorly balanced diet or the side effect of medication which do not support the growth and function of beneficial bacteria, also known as probiotics. Instead an overgrowth of potentially harmful bacteria is favoured: known as ‘dysbiosis’. There is a condition know as “leaky gut” or intestinal permeability which, in athletes, can result from endurance training. In this scenario, blood is diverted away from the gut during exercise to the exercising muscles. After stopping exercise, blood flow is restored to the gut resulting in a mild reperfusion injury. This results in a slightly “leaky gut” so that unwanted bacteria in the gut can pass into the body and provoke an inflammatory response. Equally this situation can also result in compromised absorption of nutrients in the gut, which has negative implications for health. Although a degree of inflammatory response supports desirable adaptations to exercise, clearly an excessive response will be counter-productive to improving sports performance.

The gut microbiota has also been reported to regulate immune function. Athletes in heavy training can experience suppressed functional immunity so any strategies to support the gut microbiota will potentially be beneficial in preventing infection.

Finally, recent research1 demonstrates that elite level cyclists host distinct clusters of microbiome communities when compared to controls, which contribute to more effective metabolic pathways. So optimising your gut bacteria balance may benefit your endurance performance.

Nutrition and your microbiome

What can you do to support a beneficial gut microbiota to support health and sport performance?

  • Try to include at least one fermented food source in your diet every day to boost your probiotic bacteria. Try sourdough bread, yogurt, kefir (similar to yogurt), sauerkraut, kimchi (Korean fermented vegetables), tempeh and miso (fermented soya products) and kombucha (fermented teas). These products can be found in health food shops and are becoming more widely available in some supermarkets and lunch places.
  • Regularly eat pre-biotic foods like garlic, onion, leeks, chickpeas, beans and lentils. These provide fuel for your probiotic bacteria, enabling them to proliferate.
  • Have adequate fibre in your diet from a wide variety of plant foods: eg wholegrains, legumes, vegetables, fruits, nuts, seeds. Dietary fibre is fermented by your probiotic bacteria to produce short chain fatty acids (SCFAs) which play a key role in keeping your gut healthy.
  • Consume foods and drinks rich in polyphenols: eg berries, green tea, coffee, black tea, red wine, dark chocolate, apples. Polyphenols, found in many plant foods, have been shown to help increase probiotic bacteria in the gut.
  • Take a good quality, multi-species probiotic supplement during winter, heavy training blocks and when travelling abroad, especially for races. To find out more about the potential benefits of probiotic supplementation for athletes, see my blog on probiotics here.


Dr Nicky Keay BA, MA (Cantab), MB, BChir, MRCP, medical doctor with expertise in sports endocrinology, offering a private endocrine advisory service to athletes. For further details please visit

Jo Scott-Dalgleish BSc (Hons) is a BANT Registered Nutritionist, writing and giving talks about nutrition for endurance sportBased in London, she also works as a Registered Nutritional Therapist, conducting onetoone consultations with triathletes, distance runners and cyclists to help them eat well, be healthy and perform better through the creation of an individual nutritional plan. To learn more about these consultations, please visit

To find out more about the interaction between Health, Hormones and Human Performance come to the British Association of Sport and Exercise Medicine annual conference   


1 Petersen et al. Community characteristics of the gut microbiomes of competitive cyclists. Microbiome. 2017. 5:98

Further Reading

Ubiquitous Microbiome: impact on health, sport performance and disease Dr N Keay

Endocrine system: balance and interplay in response to exercise training Dr N Keay

Inflammation: Why and How Much? Dr N. Keay, British Association of Sport and Exercise Medicine 2017