Bacteria of the species Roseburia inulinivorans have been shown to directly influence muscle mass and the size of muscle fibers. This microorganism alters the metabolism of complex amino acids and promotes the growth of fast-twitch muscle fibers. The presence of this bacterium in the gut of elderly individuals was strongly correlated with greater muscle strength.

Sarcopenia, characterized by the loss of muscle mass with age, leads to reduced mobility, increased risk of injury from falls, and a decline in overall health. To combat this condition, therapeutic exercise and high-protein diets are commonly recommended.

In recent years, researchers have been actively studying the impact of gut microbiota on metabolism and the development of various diseases, including heart and nervous system disorders. As a result, hypotheses about the influence of the gut microbiome on physical parameters of the body are being tested.

In a new study, stool samples were collected from 90 healthy individuals aged 18 to 25 and from 33 people over 65. Participants underwent tests for leg and hand strength, as well as for cardiorespiratory endurance. Genomic analysis of the microbiota revealed a positive association between the presence of Roseburia bacteria and muscle strength, but a significant effect was observed only with the R. inulinivorans strain. Other strains did not affect athletic performance.

Elderly participants with R. inulinivorans in their gut demonstrated grip strength 29% higher than their peers without this microorganism. With age, the proportion of this bacterium in the body decreased: in young people it reached 6.6%, while in the elderly it did not exceed 1.3%.

To study the causal relationship, experiments were conducted on 32 male mice. After eliminating their native gut flora with antibiotics, the animals were divided into four groups: three received different types of Roseburia bacteria, and one served as a control. The experiment lasted eight weeks.

Mice that received R. inulinivorans showed a 30% increase in forelimb grip strength after four weeks compared to the control group. This effect persisted until the end of the observation period, while other bacterial strains did not produce similar results.

Histological analysis showed an increase in the average size of muscle fibers and the proportion of fast-twitch type II cells, which are responsible for short, powerful movements. Metabolic analysis revealed that the activity of R. inulinivorans required larger amounts of available amino acids, which were actively consumed in the cecum of the mice. The reduction in amino acid levels in the gut triggered a compensatory response in the body, activating chemical pathways for purine and pentose phosphate processing, providing additional energy for intensive nucleotide biosynthesis and supporting cell growth.

Stable colonization of rodents' intestines with human strains of these bacteria has not yet been achieved. The physical effect was observed only during the course of microorganism administration, and the chemical signaling pathways from the gut to the muscles remain incompletely understood.

The study confirmed a biological link between a specific bacterium and the development of muscle mass. The R. inulinivorans species is considered a promising candidate for the development of clinical probiotics aimed at combating age-related frailty and protein loss.