The gut microbiome is an incredible thing: around 37 trillion microbes living largely in our lower intestines and weighing in at approximately 2 kilograms. Given we have only 30 trillion human cells in our bodies, one would expect the microbiome to have some big biological effects. And that’s what we see. This ecosystem of bacteria, viruses, fungi, archaea and eukaryotes affects many aspects of our health from our immune systems, energy use, mood, oxidative stress, ageing and of course our gut health.

It is unsurprising that our diet affects our microbiome.  After all what we eat becomes the environment the microbes live in and a source of their nutrients too. But what about that other staple of a healthy lifestyle - exercise? Does that affect our microbiome?

We’ve looked at the scientific literature that addresses this specific question. The answer may surprise you.

How might exercise have these effects?

More research is need to clarify the mechanisms that underpin the changes seen in the microbiome with regular exerise. But some possibile candiates are:

• Exercise increases the motility of the gut - making the contents move through faster and perhaps be mixed more thoroughly.

• Exercise affects the amount of bile acid released changing the chemistry of the gut’s contents.

• Exercise affects the immune cells found in the intestine and the ant-inflammatory chemicals they produce.

• Blood flow away from the gut during exercise and the rise in body temperature indirectly affect the gut the microbiome through changes in the intestinal cells and the integrity of the gut barrier.

• Metabolites such as lactic acid may be absorbed into the gut and affect the microbes.

• Exercise may ‘train’ the gut cells to form a more resilient gut barrier in the longer term.

How might the microbiome changes impact health?

Researchers have speculated that the microbiome changes caused by exercise have far reaching effects on gut and general health.

Akkermansia muciniphila has been associated with a lean body mass index (BMI) and improved metabolic health.

We mentioned how SCFAs, especially butyrate, strengthen the gut barrier. Mouse studies have shown that it can also promote the death of colon cancer cells. This may be the mechanism by which exercise reduces colon cancer risk.

Butyrate also reduces pro-inflammatory cytokines and oxidative stress in the gut. Researchers have speculated that it may have beneficial effects on Crohn’s disease as well as insulin resistance and immune health, but more research is needed.

Key takeaways

Written by: Dr Mary Webberley, Chief Scientific Officer at Noisy Guts. Mary has a background in biology, with two degrees from the University of Cambridge and post-doctoral research experience. She spent several years undertaking research into the diagnosis of IBS and IBD. She was the winner of the 2018 CSIRO Breakout Female Scientist Award.

Key papers:

Dziewiecka, H., Buttar, H.S., Kasperska, A. et al. Physical activity induced alterations of gut microbiota in humans: a systematic review. BMC Sports Sci Med Rehabil 14, 122 (2022). https://doi.org/10.1186/s13102-022-00513-2

Mailing LJ, Allen JM, Buford TW, Fields CJ, Woods JA. Exercise and the Gut Microbiome: A Review of the Evidence, Potential Mechanisms, and Implications for Human Health. Exerc Sport Sci Rev. 2019 Apr;47(2):75-85. doi: 10.1249/JES.0000000000000183. PMID: 30883471.