The trillions of microbes living in the human gut are increasingly recognised as important partners in human health. Scientists have linked the gut microbiome to several aspects of health, from metabolism and immunity to mental health.
A recent study suggests that these microbes may also influence an important aspect of fitness – muscle strength.
Muscle strength is a crucial feature of health for many reasons. It supports our joints and keeps our bones healthy, boosts athletic performance and even plays a role in metabolic health.
Muscle strength also helps us maintain independence later in life. As muscles gradually weaken as we get older, everyday tasks become harder and the risk of falls increases. Understanding what influences muscle strength is therefore an important part of healthy ageing research.
Read more: Muscle is important for good health – here’s how to maintain it after middle age
A recent study explored whether specific gut bacteria might be linked to muscle strength. Researchers analysed the gut microbiomes of two groups of adults: 90 young adults aged 18 to 25 and 33 older adults aged 65 to 75.
Participants provided stool samples so researchers could identify the microbes living in their gut. The researchers used DNA sequencing to read genetic material from the microbes in each sample. By comparing these sequences with large reference databases, they could determine which bacterial species were present and how abundant they were.
Participants also completed several tests designed to measure muscle strength, including a handgrip test. This involves squeezing a handheld device as hard as possible. Grip strength is widely used in health research because it provides a snapshot of overall muscle strength. Lower grip strength has also been linked to a higher risk of premature death.
When the researchers compared participants’ muscle strength with the microbes in their gut, one species stood out. Higher levels of a bacterium called Roseburia inulinivorans were linked to stronger performance across muscle strength measures.
Finding a link like this is interesting, but it does not necessarily mean the microbe is responsible. Many things can be associated without one directly causing the other. Ice-cream sales and shark attacks both increase during summer, for example – but eating ice cream does not cause shark attacks.
So to investigate whether the bacterium might actually influence muscle strength, the researchers carried out additional experiments in mice. After reducing the animals’ existing gut microbes, they introduced Roseburia inulinivorans into the mice’s digestive systems.
Mice that received the bacterium developed noticeably stronger grip strength in their arms than those that did not. Their muscle fibres also became larger and shifted toward a type of fibre associated with more powerful movements (called type II muscle fibres).
Further analysis suggested Roseburia inulinivorans may influence how muscles use energy. In mice given R inulinivorans, several energy‑related pathways inside muscle cells became more active. At the same time, levels of certain amino acids (molecules used by all living things to make proteins) decreased in the gut and bloodstream.
Older participants had lower levels of R inulinivorans. Krakenimages.com/ Shutterstock
The human data revealed another interesting pattern. Older adults in the study tended to have lower levels of Roseburia inulinivorans in their gut microbiome than the younger participants. This fits with the broader pattern of declining muscle strength that commonly occurs with age.
In humans, it’s still unclear whether gut bacteria influence muscle strength or whether stronger, more active people simply have different microbes in their gut. But the mouse experiments hint that this microbe can directly enhance muscle strength, so larger human studies will be needed to work out the direction of the relationship.
Muscle microbes
One possibility raised by this research is the future use of probiotics. These products contain live microbes intended to benefit health. If further studies confirm that Roseburia inulinivorans supports muscle strength in humans, it could be developed into a probiotic designed to help maintain muscle function as people age.
However, supplements are not the only way to encourage beneficial microbes in the gut. Diet plays a major role in shaping the microbiome.
Prebiotic fibres, which serve as food for gut bacteria, can also support their growth. This is because feeding these microbes allows them to become more established and active in the gut.
The name inulinivorans provides a clue about this bacterium’s preferred food source. It refers to inulin, a type of dietary fibre found naturally in foods such as onions, garlic, leeks, asparagus and chicory root. These fibres are known to support the growth of other beneficial gut bacteria, including members of the Roseburia group.
High‑fibre diets have long been associated with a range of health benefits. A large amount of research has linked higher fibre intake with lower risks of heart disease, type 2 diabetes and some cancers. These effects are probably driven by the complex activity of many different microbes rather than a single species. So at the moment, supplementation of any one individual bacterium is not a replacement for a diet high in fibre.
The study does have some limitations to note, however. The human groups were relatively small, and the experiments demonstrating cause and effect were conducted in mice rather than people. The older adults included in the study were also all male. Even so, the findings add to growing evidence that the gut microbiome may influence far more aspects of health than previously thought.
For now, the advice for supporting both muscle strength and a healthy microbiome remains reassuringly familiar: regular strength‑building exercise and a diet rich in fibre.
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