Researchers discovered that a specific type of gut bacteria called Limosilactobacillus reuteri ATG-F4 might help prevent muscles from shrinking when they’re not being used. In a study with mice that had immobilized limbs, the bacteria helped preserve muscle strength and size. The bacteria appears to work by boosting the body’s ability to build muscle proteins while reducing muscle breakdown. It also changed the mix of bacteria in the gut and increased helpful substances called short-chain fatty acids. While these results are promising, this research was done in mice, so scientists need to test whether it works the same way in humans before people can use it as a treatment.

The Quick Take

  • What they studied: Whether a specific gut bacteria could prevent muscles from getting smaller and weaker when they can’t be used
  • Who participated: Laboratory mice that had one limb immobilized (unable to move) to simulate muscle disuse, compared to control mice without immobilization
  • Key finding: Mice that received the ATG-F4 bacteria maintained significantly more muscle mass and grip strength compared to mice without the bacteria, even though both groups had immobilized limbs
  • What it means for you: This suggests that probiotics might one day help people prevent muscle loss during bed rest, injury recovery, or aging, but human studies are needed first to confirm these results work the same way in people

The Research Details

Scientists used laboratory mice to test whether a specific gut bacteria could protect muscles from shrinking. They immobilized one limb in some mice to simulate what happens when people can’t move due to injury or illness. Some mice received the ATG-F4 bacteria while others didn’t. The researchers then measured muscle strength, muscle size, and examined what was happening inside the muscle cells and gut.

They looked at several things: how strong the mice’s grip was, how much muscle tissue remained, what proteins were being made or broken down in the muscles, and how the bacteria changed the composition of the gut microbiome. They also measured special compounds called short-chain fatty acids that gut bacteria produce.

This approach is important because it helps scientists understand the connection between gut health and muscle health. By studying mice first, researchers can figure out how the bacteria works before testing it in humans. The study examined both the muscle changes and the gut changes, which helps explain the complete picture of how this bacteria might help.

This is laboratory research in animals, which is an important first step but not the final answer. The study appears to be well-designed with measurements of multiple factors (muscle strength, muscle size, protein synthesis, and gut bacteria changes). However, results in mice don’t always translate directly to humans, so more research is needed. The journal is a peer-reviewed scientific publication, which means other experts reviewed the work before publication.

What the Results Show

Mice that received the ATG-F4 bacteria showed significantly better preservation of muscle mass compared to mice without the bacteria, even though both groups had immobilized limbs. The treated mice also maintained better grip strength and muscle endurance. Inside the muscle cells, the bacteria activated a pathway called mTOR that helps build muscle proteins, while also reducing a factor called MuRF1 that normally breaks down muscle during disuse.

The bacteria also changed which types of bacteria lived in the mice’s guts. Specifically, it increased beneficial bacteria from the Muribaculaceae family while decreasing less helpful bacteria. This shift in the bacterial community led to increased production of short-chain fatty acids, particularly butyrate and acetate, which have anti-inflammatory properties and support muscle health.

The study found that the gut bacteria changes were connected to the muscle benefits. The increased short-chain fatty acids appear to be one way the bacteria helps muscles stay strong. These fatty acids are known to reduce inflammation throughout the body and support the immune system, which may indirectly help preserve muscle. The researchers suggest the bacteria works through multiple pathways: directly boosting muscle protein production, reducing muscle protein breakdown, and improving the overall gut-muscle communication system.

This research builds on growing evidence that gut bacteria influence muscle health and that probiotics may help prevent muscle loss. Previous studies have suggested connections between gut health and muscle strength, but this is one of the first to specifically test this particular bacteria strain. The findings align with other research showing that short-chain fatty acids support muscle function, adding another piece to the puzzle of how gut bacteria affect overall body health.

The biggest limitation is that this study was done in mice, not humans. Mice have different body systems and metabolisms than people, so results may not translate directly. The study doesn’t specify exactly how many mice were used, which makes it harder to assess the strength of the findings. Additionally, the study only looked at one type of muscle disuse (immobilization), so it’s unclear whether the bacteria would help with muscle loss from aging or disease. Finally, this is a single study, so the findings need to be confirmed by other independent research teams before drawing firm conclusions.

The Bottom Line

Based on this research, there is currently no recommendation to use this specific bacteria as a treatment, since it has only been tested in mice. However, the findings suggest it’s worth pursuing human studies. In the meantime, the best evidence-based approaches to prevent muscle loss remain regular physical activity, adequate protein intake, and maintaining overall health. If you’re concerned about muscle loss due to immobility or aging, talk to your doctor about proven strategies.

This research is most relevant to people concerned about muscle loss from bed rest, injury recovery, aging, or disease. It’s also important for researchers and doctors looking for new treatment approaches. However, until human studies are completed, this remains a laboratory finding rather than a practical treatment option. People should not seek out this specific bacteria strain based on this single animal study.

Since this is early-stage research in animals, it will likely take several years before human studies could begin, and several more years before any potential treatment might become available. Realistic expectations are that if this bacteria does work in humans, it would likely take months of consistent use to see meaningful effects on muscle preservation, similar to how other probiotics work.

Want to Apply This Research?

  • Users could track grip strength weekly using a simple hand dynamometer (a device that measures grip strength) and record measurements in the app, along with notes about activity level and any periods of reduced mobility
  • Users could set reminders to maintain regular physical activity and track daily movement minutes, while also monitoring their protein intake at meals—these proven strategies work alongside any future probiotic treatments
  • Create a long-term tracking dashboard that monitors grip strength trends, muscle-related symptoms (like fatigue or weakness), activity levels, and nutritional intake over months, allowing users to see patterns and share data with healthcare providers

This research was conducted in laboratory mice and has not been tested in humans. The findings are preliminary and should not be used as a basis for personal health decisions. Do not attempt to obtain or use this specific bacterial strain without medical supervision. If you are experiencing muscle loss, weakness, or immobility, consult with a healthcare provider about evidence-based treatment options. This article is for informational purposes only and does not constitute medical advice.