Steroids like dexamethasone can cause muscles to shrink and weaken, a problem for people taking these medications long-term. Researchers discovered that a specific type of bacteria called Propionibacterium freudenreichii MJ2 might help prevent this muscle loss. In lab tests and rat studies, this bacteria helped maintain muscle size and strength even when steroids were being used. The bacteria worked by turning off genes that cause muscle breakdown and turning on processes that build muscle back up. While these results are promising, more research in humans is needed before this becomes a treatment option.

The Quick Take

  • What they studied: Whether a specific type of bacteria could prevent muscles from shrinking when people take steroids (specifically dexamethasone)
  • Who participated: Laboratory muscle cells and rats that were given steroids to cause muscle loss. The exact number of rats wasn’t specified in the abstract
  • Key finding: Both live and heat-killed versions of the bacteria helped rats maintain muscle mass and strength, and prevented muscle fiber shrinkage compared to rats that only received steroids
  • What it means for you: This research suggests a potential new way to protect muscles in people who must take steroids for medical reasons, but human studies are still needed. Don’t change your steroid use based on this—talk to your doctor first

The Research Details

The researchers used two different approaches to test their idea. First, they used laboratory-grown muscle cells and exposed them to steroids while also treating them with the bacteria. They measured whether the muscle cells stayed healthy and looked at which genes turned on and off. Second, they gave rats steroids to cause muscle loss, then treated some rats with the bacteria (both living and heat-killed versions) to see if it helped. They measured the rats’ grip strength, total muscle mass, and the size of individual muscle fibers.

The heat-killed bacteria is important because it means you wouldn’t need living bacteria—just the components from the bacteria might be enough to help. This makes it safer and easier to use as a potential medicine.

The researchers looked at specific genes and proteins involved in muscle breakdown and muscle building to understand how the bacteria was working at the cellular level.

This research matters because steroids are important medicines for treating inflammation, autoimmune diseases, and other serious conditions, but muscle loss is a major side effect that affects quality of life. Finding a way to prevent this side effect could help millions of people who need steroids. Using bacteria or bacterial components as medicine is a growing field, and this study shows it might work for muscle protection.

This study used both cell culture and animal models, which is good for understanding how something works. However, the abstract doesn’t specify how many rats were used, which makes it harder to judge the strength of the results. The study was published in a peer-reviewed journal, meaning other scientists reviewed it. The biggest limitation is that this hasn’t been tested in humans yet, so we don’t know if it will actually work in people

What the Results Show

In the laboratory muscle cells, the heat-killed bacteria prevented the muscle fibers from getting smaller when exposed to steroids. It also stopped the activation of genes that normally cause muscles to break down (MuRF-1 and Atrogin-1) and genes that cause cell death (Bax/Bcl-2). At the same time, the bacteria activated proteins that help build new muscle (p-Akt/Akt and p-mTOR/mTOR).

In the rats, both living and heat-killed versions of the bacteria improved the results. Rats treated with the bacteria had better grip strength (a measure of muscle function), more total muscle mass, and larger individual muscle fibers compared to rats that only received steroids without the bacteria treatment.

The fact that both living and heat-killed bacteria worked is significant because it suggests the beneficial parts of the bacteria can survive processing, making it potentially easier to develop as a medicine.

The study showed that the bacteria’s protective effect worked through multiple pathways—it didn’t just work one way. This suggests the bacteria has multiple mechanisms to help muscles, which could make it more effective than a single-target drug. The researchers also found that the bacteria could reduce markers of cell death in muscle tissue, suggesting it protects muscle cells from dying.

Previous research has shown that Propionibacterium freudenreichii has anti-inflammatory and anti-obesity properties. This study extends that knowledge by showing it also has muscle-protective properties. The specific genes and proteins the bacteria affects align with what scientists already know about how muscles grow and shrink, which makes the findings more believable. However, most previous work has been in animals or cells, not humans.

The biggest limitation is that this research was only done in rats and laboratory cells, not in humans. Rats don’t always respond the same way humans do to treatments. The abstract doesn’t specify how many rats were used or provide detailed statistical information about how confident we should be in the results. We also don’t know the optimal dose or how long the treatment would need to continue. The study used only one type of steroid (dexamethasone), so we don’t know if it would work with other steroids

The Bottom Line

This research is preliminary and promising but not ready for human use. Current recommendation: Continue taking steroids as prescribed by your doctor if medically necessary. Do not attempt to use this bacteria as a treatment without medical supervision. If you’re concerned about steroid-related muscle loss, talk to your doctor about exercise programs and nutrition strategies that are proven to help. Confidence level: Low for human application (animal studies only)

People who take steroids long-term for conditions like rheumatoid arthritis, lupus, or severe asthma should find this interesting. Older adults concerned about muscle loss might also benefit from future developments. People with normal muscle function who don’t take steroids don’t need to worry about this research right now

In the rat studies, the protective effects appeared to develop over the treatment period, but the exact timeline isn’t clear from the abstract. If this ever becomes a human treatment, it would likely take 5-10 years of additional research before it’s available

Want to Apply This Research?

  • Track grip strength weekly using a simple hand dynamometer (available inexpensively online) and log the results. Also track perceived muscle strength with simple tests like how many push-ups or squats you can do
  • If you take steroids, use the app to set reminders for resistance exercises (weight training or bodyweight exercises) 3-4 times per week, which is proven to help prevent steroid-related muscle loss. Log your exercise sessions and any muscle soreness
  • Create a monthly report comparing grip strength and exercise performance. Take progress photos monthly. If you’re on long-term steroids, discuss these tracking metrics with your doctor at each visit to monitor for muscle loss

This research is preliminary and has only been tested in animals and laboratory cells, not in humans. Do not use any bacterial supplements or change your steroid medication based on this study. If you take steroids and are concerned about muscle loss, consult your healthcare provider about safe, proven strategies like exercise and proper nutrition. Always talk to your doctor before starting any new supplement or treatment, especially if you have existing health conditions or take other medications. This information is for educational purposes only and should not replace professional medical advice.