Billions of bacteria live in our gut. We know they digest fibre and train the immune system. We are now discovering that they send messages all the way into our mitochondria, and that some of these messages do good, others harm.
The first systematic review on the subject
In August 2026, two American researchers combed through every published study on the substances made by gut bacteria and their direct effect on mitochondria. Their conclusion, published in Gut Microbes: four of these substances have an established effect with a moderate level of evidence.
Two are beneficial. Butyrate and propionate, produced when bacteria ferment dietary fibre, stimulate the production of new mitochondria and energy output. Two are harmful. Indoxyl sulfate, from the breakdown of proteins, and LPS, a fragment of bacterial wall, damage mitochondria and fuel inflammation.
A well-fed gut is a sealed gut
Butyrate is also the favourite fuel of the cells lining the colon. Well fed, these cells keep their junctions tight and the gut stays sealed. Another review from May 2026 turns the usual perspective around: it is the mitochondria of the gut cells that, by consuming oxygen, create the low-oxygen environment in which the good bacteria thrive. When these mitochondria weaken, oxygen rises and harmful bacteria take over. Dysbiosis would therefore be as much a consequence as a cause.
A circle, not a line
Good bacteria, butyrate, sturdy gut cells, healthy mitochondria, an environment that favours good bacteria: it is a circle. It turns the right way when the diet provides enough fibre, and the wrong way under a poor diet, repeated antibiotics or chronic stress. The authors point out that most of the data comes from laboratory and animal studies.
Key points
- Gut bacteria make substances that reach the mitochondria directly.
- Butyrate, from fibre, is the most beneficial; LPS and indoxyl sulfate are the most harmful.
- The gut's own mitochondria maintain the environment in which good bacteria live.
- Dietary fibre is the simplest entry point into this virtuous circle.
Sources
- Frye RE, Rossignol DA. Mechanistic pathways linking gut microbial metabolites, microbial structural products, and host-microbe co-metabolites to mitochondrial function. Gut Microbes, 2026. https://doi.org/10.1080/19490976.2026.2694140
- Ma Z et al. Host metabolism shapes the intestinal microbiota: a top-down paradigm of environmental selection pressure. Gut Microbes, 2026. https://doi.org/10.1080/19490976.2026.2667735
- Han EJ et al. The gut microbiome and mitochondrial function in metabolism, immunity, and disease. Gut Microbes, 2026. https://doi.org/10.1080/19490976.2026.2699451
