Data published in Gut suggested that Roseburia inulinivorans is associated with improved human muscle strength, notably an increased abundance in younger adults with higher grip strength and VO2max.
The bacterial species was also positively associated with leg press and bench press strength.
In older adults, detectable levels of R. inulinivorans in stool samples were associated with a 29% higher handgrip strength compared to those without the bug. This was observed without an accompanying increase in peak oxygen uptake, indicating better fitness.
Moreover, data from mice studies found that supplementation with R. inulinivorans led to increases in muscle strength and fiber size.
“These beneficial effects were accompanied by plasma alterations in amino acid and carbohydrate metabolism, including enrichment of the muscle purine and PPPs [pentose phosphate pathways], which are central to energy production, redox balance and nucleotide biosynthesis,” wrote scientists from the University of Almería and the University of Granada in Spain and Leiden University Medical Center in the Netherlands.
“Collectively, our findings provide robust evidence supporting a gut-muscle axis in which R. inulinivorans positively modulates muscle metabolism and muscle strength.”
Mining the microbiome
The link between the gut microbiome and athletic performance—and the potential of modulation of the microbiota via pre- and probiotics to boost performance—is an area of increasing interest.
Data from scientists at University College Cork in Ireland in 2014 found that the gut microbiomes of professional Irish rugby players were significantly more diverse than non-athletes.
A follow-on study performed in collaboration with scientists at Imperial College London in England (published in 2018 in Gut) found the differences between athletes and sedentary people is “even more evident at the functional or metabolic level.”
Since these early studies, research has expanded to explore if specific species or strains may exert benefits for athletic performance and if a gut microbiome-muscle axis exists.
Commenting independently on the new study, Dr. Orla O’Sullivan, research fellow at the Teagasc Food Research Centre in Ireland and co-author on the 2014 rugby paper, told NutraIngredients that the data identifies Roseburia inulinivorans as a potential next-generation probiotic.
“The study is a significant advancement in the field of athlete gut microbiome research in that it associates mechanism to improved athletic function,” she said. “As the authors point out more longitudinal studies are essential to determine if this is cause or consequence and also dose response studies to determine to level of R. inulinivorans needed.”
Study details
The researchers analyzed stool samples from 90 healthy young (18-25 year olds) and 33 older (65+) adults and correlated this with hand grip strength, leg press and bench press performance, and VO2 max (maximal oxygen consumption during exertion—a measure of cardiorespiratory fitness).
The data showed that the Roseburia group (genus) was the only one that was positively associated with muscle mass and strength. The abundance of R. inulinivorans in younger adults ranged from 0% to 6.6%, and a greater abundance of R. inulinivorans in this age group was positively associated with both handgrip strength and VO₂ max.
In older adults, the bacterium is less abundant than in young adults, suggesting that its levels may decrease with age, a period in which muscle mass is lost. Specifically, R. inulinivorans ranged from 0% to 1.3%. Those with detectable levels of the bacterium were found to have a significantly greater handgrip strength compared to those with no detectable R. inulinivorans.
“This opens up the possibility that the bacterium under investigation could be used as a probiotic to help preserve muscle strength during aging,” stated Borja Martínez Téllez, a researcher at the University of Almería, in a press release.
To explore a potential causal role for Roseburia in muscle strength, the researchers fed Roseburia species once a week for eight weeks to 32 mice that had previously been given a cocktail of antibiotics for a fortnight to deplete their gut microbiome.
Lab mice were randomly divided into groups: Three groups received a different Roseburia species, while the fourth group received no Roseburia and acted as the control.
While none of the Roseburia species were found to boost running time to exhaustion, R. inulinivorans supplementation was linked to a 30% increase in forelimb grip strength after four, six and eight weeks, compared to the control.
In addition, mice fed R. inulinivorans had larger muscle fiber size and a significantly higher proportion of type II fibers in their calf muscles, compared with the other groups. These changes were also accompanied by metabolic changes in the proteins and enzymes key to muscle energy production.
“Taken together, our findings provide solid evidence confirming the existence of a gut-muscle axis in which this identified bacterium positively modulates muscle metabolism and muscle strength,” stated Jonatan Ruiz, professor in the Department of Physical Education and Sport at the University of Granada and researcher at the Joint University Institute for Sport and Health (iMUDS), in a press release.
A note of caution
Dr. Ralf Jäger, managing member of Increnovo LLC and lead author on the International Society of Sports Nutrition Position Stand: Probiotics, called the study interesting but added a note of caution, telling NutraIngredients that there is a question of translational relevance of the antibiotic-treated mouse model used in the study.
“While the mouse experiments provide evidence for causality, the animals were pretreated with broad-spectrum antibiotics prior to Roseburia inulinivorans administration,” Dr. Jäger said. “This approach reduces colonization resistance of the introduced bacterium but creates an artificial microbiome context that differs substantially from the intact microbial ecosystems present in humans. Consequently, it remains uncertain whether R. inulinivorans supplementation would successfully colonize or exert similar physiological effects in individuals with an established microbiota.”
Turning his attention to the human data in the study, Dr. Jäger said that this is largely observational and cross-sectional, and that the abundance of Roseburia is strongly influenced by dietary fiber intake and overall dietary patterns. People with higher fiber intake or healthier lifestyles may simultaneously have greater Roseburia abundance and superior physical fitness.
He noted that while the authors did adjust for several covariates, residual confounding by diet, exercise habits and metabolic health cannot be excluded, limiting causal interpretation of the association between R. inulinivorans and muscle strength.
“Finally, the proposed mechanism linking R. inulinivorans to improved muscle function appears to involve microbial metabolite production and host metabolic modulation,” he added. “Because many gut microbes produce similar metabolites (e.g., short-chain fatty acids), it remains unclear whether the observed effects are species-specific or reflect broader microbial metabolic activity. Identifying the precise metabolic mediators will be essential before translating these findings into probiotic, prebiotic or metabolite-based interventions targeting muscle function or sarcopenia.”
Source: Gut. doi: 10.1136/gutjnl-2025-336980. “Roseburia inulinivorans increases muscle strength”. Authors: B. Martinez-Tellez, et al.
