Ruth James
by Ruth James

As athletes, it can be easy to forget about our gut flora and the important role it plays in our health. We all have our very own special mix of microbial inhabitants. Gut health may influence not only our digestion, but also our immunity to withstand stress associated particularly with over training, nutrition absorption and recovery. There is some evidence to suggest it might even improve brain function.


Around 100 trillion microbes including bacteria, virus algae, fungi live in our gut which is collectively called the gut microbiome. Our gut bacteria weighs over 1 kg.

Currently the gut microbiome is a hot topic attracting a lot of scientific research but there are also many myths circulating about gut health and with few studies on humans, care must be applied to the athlete.

Gut health has been a big focus in athletic research as heavy exercise can result in gut symptoms such as diarrhoea, cramps, pain and bloating which can adversely affect athletic performance.

Gut microbiota ferment complex dietary starches, releasing energy and thereby increasing endurance performance by maintaining glycaemia over time delaying fatigue symptoms.

A lot of what we eat is digested by our microbes and then they produce other nutrients which are very important to us.

Interestingly unlike our human genome (or make up) our microbial genome can change according to our diet, the use of pro and prebiotics and antibiotics.

We know that our diet influences the microorganisms in our gut both short term and long term and that diets composed of either animal or vegetable plant products alters the microbiome.

Crucially an athlete’s microbiomes are distinctly different from those of non-athletes. It seems the more active you are the more diverse your microbiome will be. And interestingly there have been several research studies in athletes including rowers which found differences in the gut even between different sports.

Analysing your gut microbiome to predict future performance may become common practice in the next decade and could be just like taking a blood sample. Diets and supplements such as probiotics may need to be tailored to the individual athlete to maximise their own gut microbiota.

What about Probiotics?

There are a range of nutrition supplement strategies employed by athletes to improve gut health and immune function. Of these, probiotic supplements are among the most popular. Probiotics have an established history of use for preventing gastro-intestinal illness, particularly traveller’s diarrhoea and antibiotic associated diarrhoea. Probiotics contain friendly microorganisms which boost the diversity of good bacteria, yeast and fungi living in our guts. Research has also focused on the effects of probiotics on immune function in athletes examining whether probiotics reduce upper respiratory tract illness (URTI). While promising results have been observed in relation to URTI the overall changes observed in immune activity are mixed.

And Prebiotics?

Prebiotics are non-digestible polysaccharides that stimulate the growth and activity of the gut microbiota. A number of foods have a prebiotic effect, including chickpeas, lentils, barley, bananas, oats, wheat, soy-beans, asparagus, leek, chicory, garlic, artichoke and onion.

Whilst the use of probiotics has traditionally been focused on gut health this may now be extended to inflammatory and metabolic effects by modifying the microbiota thus enhancing athlete performance. There are capsules, tablets and readymade live yoghurts on the market but also lots of different products containing probiotics e.g. kefir, kombucha, kimchi, sauerkraut in various forms such as pickles, milks or drinks. Its big business.

Intense Training/Gastric Stress.

While gastric stress is widely recognized as the bane of long-distance runners, it also appears to be common in other elite endurance athletes with symptoms such as abdominal bloating, pain, diarrhoea and gassiness.

Causes of gastric upset are not completely understood they may be due to a range of different reasons e.g:


– There is reduced blood flow from the gut to the muscles and anxiety affects hormones and gut mobility


–  When the impact of running creates  a physical problem


 High fibre, fat, protein or fructose and beverages/sports drinks with a high density (>500mOsmoles/L)

Key Points

  • Eating real food is important: processed convenience fast foods may not contain all the microbes we need for a healthy gut and may contain other things like emulsifiers which may prevent absorption.
  • Avoid high fructose fruit juices. Check the label.
  • Do not try new nutrition strategies for race day: practice well in advance and train your gut during training.
  • Eat a variety of different rainbow coloured foods and be adventurous and try different foods every week: a healthy gut likes diversity in foods.
  • Eat minimum of 5 vegetables per daywith lots of polyphenols e.g. berries , legumes and vegetables.
  • A day prior to competition: A) avoid high fibre containing foods g.wholemeal bread, brown rice and pasta and choose white bread, white rice or pasta instead.The roughage takes time to digest and may cause gut discomfort; B) Consume less fruit and vegetables leading up to competition or remove skins and mash up vegetables; C) Minimise milk products and thus lactose consumption and substitute almond, soy and rice milks.
  • Minimise stress in your life and sleep.
  • Ignore fad diets and media hype.
  • Athletes are advised to work with their dietitians to modify their diet and determine whether supplements, such as probiotics and prebiotics, may be useful during prolonged exercise, periods of heavy training, and during competition and travel.


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