exercise and the gut: the full lowdown

What does exercise have to do with your gut?

We all know exercise plays an important part in our overall health – it reduces the risk of chronic disease, makes you happier and improves sleep quality. But how does it influence your gut and the trillions of microbes (the gut microbiota) that live there?

What does the research say?

A study in humans investigated the effect of a six-week exercise regime on microbiota composition (aka the make-up of different microbes in your gut) (1). After exercise, previously sedentary individuals had increased levels of several types of beneficial gut bacteria and the short-chain fatty acid, butyrate, which is known to reduce inflammation and promote good gut health. However, these levels returned to baseline when exercise was stopped. Overweight individuals who began exercising also displayed changes in their microbiota but these were different than lean individuals. Whilst the reasons for the differences between lean and overweight individuals aren’t fully understood, this provides evidence that exercise – independent of diet – can have a positive effect on the composition of the gut microbiota.

Other studies have aimed to investigate whether a short-term exercise programme can alter gut bacteria composition. Studies looking at the effects of light-moderate intensity training have found either no significant changes in microbiota composition (2) or only half of the participants showing microbial changes (3). This suggests that longer or more intensive exercise could be required to stimulate microbiota changes but either way, we know it is good to get moving!

Which type of exercise is best?

Exercise can be broadly split into two categories; strength-based exercises such as weight lifting, or endurance-based such as running or cycling, which aims to improve your cardiovascular fitness (essentially the ability of your heart and lungs to supply oxygen to your muscles). Studies have shown that cardiovascular fitness is positively linked with gut microbial diversity, independent of factors such as age and dietary intake (4,5) but little is known about the effect of strength training on gut health. What we do know is that diversity is key for gut health! Based on the current research, it seems as though cardio is the best form of exercise for good gut health.

Modern life can be sedentary, with technology making it easier for us to move less  and many of us sat at our desks all day. The NHS recommends 150 minutes of moderate-intensity activity per week (6). The important thing to note is that making a small change can have a positive impact. If you’ve never exercised before, research shows that increasing the frequency of moderate exercise from never to daily has been shown to increase the diversity of Firmicutes bacteria (7), one of the major types (or phyla in the science world) of bacteria.

Don’t stress

Stress has a huge impact on the gut microbiota. If you haven’t already, you can read our article on stress here.

In short, high-intensity exercise is a stress on your body, and just like other types of stress, stimulates the production of the stress hormone cortisol that negatively affects the physical workings of your gut and gut microbiota. Very high-intensity exercise may increase inflammation, which, over time can damage cells in the intestinal wall, resulting in the membrane of your gut being permeable (you may hear the expression ‘leaky gut’) to substances that shouldn’t be able to get through – like a fishing net with holes in (8). When this happens, it can increase susceptibility to diseases such as Type II diabetes and depression (9, 10) but we still need more research to fully understand how and why this happens. So if you love high-intensity exercise, think of ways to destress after, like making time to cool down or practice some breathing techniques and your gut will thank you for it.

Five Top Tips

• Start small – why not take a 20-minute stroll outside in your lunch break or think about routes that involve a bit more walking? A small change can make a difference!
• Do something you enjoy, it doesn’t have to mean pounding the treadmill or hours in the gym!
• Exercise with a friend – it’ll be more fun and you’ll be more likely to stick to it.
• Don’t overdo it – aim for slow and steady progress and allow yourself some rest too.
• Exercise isn’t a quick fix. Just as they say you can’t out-train a poor diet, you can’t out-train a poor lifestyle. The rest of your lifestyle, such as diet, stress, and sleep, influences your gut microbiota. Work on each of these factors and your gut will thank you in return.

About the author

Gina is currently a postgraduate student at Imperial College London focussing on the microbiome in health & disease.  She graduated from Durham University in 2016 after studying Natural Sciences. Following this, Gina worked at Innovate UK for two years helping to drive innovation and business growth in the health & life sciences industry.

References

1. Allen JM, Mailing LJ, Niemiro GM, Moore R, Cook MD, White BA, Holscher HD, Woods JA. Exercise alters gut microbiota composition and function in lean and obese humans. Med Sci Sports Exerc. 2018; 50(4)
2. Cronin O, Barton W, Skuse P, Penney NC, Garcia-Perez I, Murphy EF, Woods T, Nugent H, Fanning A, Melgar S, Falvey EC. A prospective metagenomic and metabolomic analysis of the impact of exercise and/or whey protein supplementation on the gut microbiome of sedentary adults. MSystems. 2018; 3(3)
3. Munukka E, Ahtiainen J, Puigbo P, Jalkanen S, Pahkala K, Rintala A, Kujala UM, Hollmén M, Huovinen P, D’Auria G, Pekkala S. Six-week endurance exercise alters gut metagenome that is not reflected in systemic metabolism in over-weight women. Frontiers in microbiology. 2018; 9(2323)
4. Estaki M, Pither J, Baumeister P, Little JP, Gill SK, Ghosh S, Ahmadi-Vand Z, Marsden KR, Gibson DL. Cardiorespiratory fitness as a predictor of intestinal microbial diversity and distinct metagenomic functions. Microbiome. 2016; 4(1)
5. Carter SJ, Hunter GR, Blackston JW, Liu N, Lefkowitz EJ, Van Der Pol WJ, Morrow CD, Paulsen JA, Rogers LQ. Gut microbiota diversity is associated with cardiorespiratory fitness in post‐primary treatment breast cancer survivors. Experimental physiology. 2019; 104(4)
6. Exercise. 2019. Retrieved from: https://www.nhs.uk/live-well/exercise/
7. Mach N, Fuster-Botella D. Endurance exercise and gut microbiota: A review. Journal of sport and health science. 2017; 6(2)
8. Costa RJ, Snipe RM, Kitic CM, Gibson PR. Systematic review: exercise‐induced gastrointestinal syndrome—implications for health and intestinal disease. Alimentary pharmacology & therapeutics. 2017; 46(3)
9. Campbell AW. Autoimmunity and the gut. Autoimmune diseases. 2014
10. Black PH. The inflammatory response is an integral part of the stress response: Implications for atherosclerosis, insulin resistance, type II diabetes and metabolic syndrome X. Brain, behavior, and immunity. 2003; 17(5)