Researchers discovered that a specific type of helpful bacteria called Lacticaseibacillus paracasei EFEL6501 might prevent muscles from shrinking and getting weaker. In laboratory tests and mouse studies, this bacteria produced substances that protected muscle cells from breaking down and helped muscles stay strong. The bacteria also changed the mix of microorganisms in the gut, increasing good bacteria and producing a helpful compound called acetate. These findings suggest this probiotic could become a natural way to fight muscle loss, especially in people taking certain medications that cause muscles to weaken.

The Quick Take

  • What they studied: Whether a specific probiotic bacteria could prevent muscles from shrinking and becoming weaker when exposed to a steroid medication that normally causes muscle loss.
  • Who participated: Laboratory muscle cells and mice treated with dexamethasone (a steroid that causes muscle loss). The exact number of mice was not specified in the abstract.
  • Key finding: Mice that received the probiotic bacteria had noticeably stronger muscles—their grip strength improved by about 10%, muscle thickness increased by about 7%, and the muscle fiber size grew by about 15% compared to mice that didn’t receive the bacteria.
  • What it means for you: This research suggests that taking this specific probiotic might help protect muscles from shrinking, particularly for people taking steroids or dealing with muscle loss. However, this is early-stage research in animals and lab cells—human studies are needed before recommending it as a treatment.

The Research Details

This research combined two different approaches to test whether the probiotic bacteria could prevent muscle loss. First, scientists grew muscle cells in laboratory dishes and exposed them to a steroid medication known to cause muscle breakdown. They then added the probiotic bacteria (or substances it produces) to see if it protected the muscle cells. Second, they conducted the same experiment in living mice, measuring actual muscle strength and size changes over time. This combination of lab and animal testing helps researchers understand both how the bacteria works at the cellular level and whether those benefits translate to real-world muscle function.

Testing in both laboratory cells and living animals is important because it shows whether a treatment works at multiple levels. Lab tests reveal the basic mechanisms—how the bacteria protects muscle cells—while animal studies show whether these benefits actually improve muscle strength and function in a living body. This two-step approach gives scientists confidence that the findings are meaningful and might eventually work in humans.

The study was published in a peer-reviewed scientific journal, which means other experts reviewed the work before publication. The researchers measured multiple important outcomes (muscle strength, muscle size, and muscle fiber area) rather than just one, which strengthens their conclusions. However, the study was conducted in animals and laboratory cells, not humans, so results may not directly apply to people. The exact number of mice tested was not provided in the abstract, making it harder to assess the study’s statistical power.

What the Results Show

When mice received the probiotic bacteria, their muscles showed significant improvements compared to mice that only received the steroid medication. Grip strength—a measure of how hard the mice could squeeze—increased from 106.87 grams to 117.87 grams, an improvement of about 10%. The thickness of the gastrocnemius muscle (the main calf muscle) grew from 5.70 millimeters to 6.09 millimeters. Most impressively, the cross-sectional area of muscle fibers (essentially the size of individual muscle cells) increased from 29.79 to 34.11 square micrometers, representing a 15% increase in muscle cell size. These improvements suggest the probiotic bacteria actively protected muscles from the steroid’s damaging effects.

The research revealed that the probiotic bacteria worked through multiple mechanisms. In laboratory muscle cells, the bacteria produced substances that reduced the breakdown of muscle proteins and enhanced the creation of new muscle proteins. In the mice’s guts, the bacteria increased the abundance of other beneficial bacteria species, including Lactobacillus reuteri, Bifidobacterium choerinum, and others. The bacteria also increased levels of acetate, a short-chain fatty acid that appears to support muscle health, rising from 1.57 to 1.97 millimolar. These findings suggest the benefits came from both direct effects on muscle cells and indirect effects through improving overall gut health.

This research builds on growing evidence that gut bacteria influence muscle health and that probiotics may help prevent muscle loss. Previous studies have shown connections between gut microbiota composition and muscle strength, but this study is notable for identifying a specific bacterial strain and demonstrating its protective effects against steroid-induced muscle loss. The findings align with emerging research showing that short-chain fatty acids like acetate support muscle function, providing a plausible explanation for how the bacteria helps muscles.

This study has several important limitations. First, it was conducted in mice and laboratory cells, not humans, so the results may not directly apply to people. Second, the abstract doesn’t specify how many mice were used, making it impossible to assess whether the sample size was adequate. Third, the study only tested one specific probiotic strain, so results may not apply to other probiotics. Fourth, the research focused on steroid-induced muscle loss; benefits for other types of muscle loss (aging, inactivity, disease) are unknown. Finally, the study doesn’t provide information about optimal dosage, duration of treatment, or potential side effects in humans.

The Bottom Line

Based on this research, we cannot yet recommend this probiotic for human use (confidence level: low). The findings are promising and warrant human clinical trials, but evidence from animal studies doesn’t always translate to people. If you’re concerned about muscle loss—especially if taking steroids—discuss probiotic options with your doctor rather than self-treating. General probiotic use may have other benefits, but this specific strain hasn’t been tested in humans yet.

This research is most relevant to people taking steroid medications long-term, older adults concerned about age-related muscle loss, and researchers studying probiotics and muscle health. People with muscle-wasting diseases, cancer patients undergoing treatment, and those recovering from surgery might eventually benefit if human studies confirm these findings. However, until human trials are completed, this remains a research finding rather than a proven treatment.

In the mouse studies, improvements in muscle strength and size were measurable within the study period, but the exact duration wasn’t specified in the abstract. If this probiotic eventually proves effective in humans, realistic expectations would likely involve weeks to months of consistent use before noticeable improvements in muscle strength or size. Individual results would vary based on age, overall health, diet, and exercise habits.

Want to Apply This Research?

  • If you’re using a probiotic supplement, track weekly grip strength measurements (using a hand dynamometer if available) or simple strength tests like how many push-ups you can do. Also monitor subjective measures like energy levels and muscle soreness. Record any changes in digestion or gut health, as these may indicate the probiotic is working.
  • Start by adding a probiotic supplement containing this specific strain (once available for human use) to your daily routine at the same time each day, paired with a consistent meal. Combine this with adequate protein intake and regular resistance exercise, as probiotics work best alongside these lifestyle factors. Track consistency of taking the supplement to ensure you’re giving it adequate time to work.
  • Establish a baseline measurement of muscle strength and function before starting any new probiotic. Measure monthly using consistent methods (same time of day, same conditions). Keep a food and supplement diary to identify any correlations between probiotic use and changes in muscle strength, energy, or digestive health. Share results with your healthcare provider to determine if the supplement is beneficial for your specific situation.

This research describes findings from laboratory and animal studies only—not human trials. This probiotic strain has not been tested for safety or effectiveness in people and is not approved as a medical treatment. Do not use this information to self-treat muscle loss or to replace prescribed medications. If you’re experiencing muscle weakness or taking steroids long-term, consult your healthcare provider before starting any new supplements. This summary is for educational purposes only and should not be considered medical advice. Always speak with a doctor before making changes to your health regimen, especially if you have existing health conditions or take medications.