What Is the Gut-Muscle Axis?

Reviewed by SOMA HEALTH's Medical Research Team

The trillions of microbes living in your gut do more than digest food. A growing body of research suggests they also communicate with your muscles, influencing how muscle tissue is built, maintained, and fueled. Scientists call this two-way relationship the gut-muscle axis, and it is reshaping how we think about strength, aging, and nutrition.

What the gut-muscle axis actually means

The gut-muscle axis is the network of chemical signals that travels between the gut microbiome and skeletal muscle. It is not a single nerve or a single hormone but a collection of pathways: molecules the bacteria produce, nutrients they help unlock, immune signals they shape, and inflammatory tone they influence. The core idea is that the composition and activity of your gut bacteria can affect muscle mass, strength, and function, and that muscle activity and diet in turn shape the gut. It is a conversation, not a one-way broadcast.

Interest in this axis has grown alongside concern about sarcopenia, the age-related loss of muscle mass and strength that undermines mobility and independence in later life. Researchers have noticed that older adults with more robust, diverse microbiomes often have better muscle measures, which raised the question of whether the gut is a contributor rather than a bystander.

How gut bacteria may influence muscle

Short-chain fatty acids

When gut bacteria ferment dietary fiber, they produce short-chain fatty acids such as butyrate, acetate, and propionate. These molecules are more than waste products. They serve as an energy source, help regulate inflammation, and appear to influence muscle metabolism and insulin sensitivity. Diets low in fiber tend to produce fewer short-chain fatty acids, which is one proposed link between poor gut health and weaker muscle outcomes. Much of the detailed mechanism here still comes from laboratory and animal models, so it should be read as a promising mechanism rather than settled human fact.

Protein and nutrient handling

Muscle is built from amino acids, and the gut is where protein is broken down and absorbed. A healthy gut lining and microbial community may support how efficiently the body extracts and uses amino acids from food. Researchers have also explored the concept of anabolic resistance, the tendency of aging muscle to respond less strongly to dietary protein, and whether the microbiome plays a role in it.

Inflammation and the immune connection

A disrupted gut barrier can allow bacterial fragments to leak into circulation, nudging the immune system toward chronic low-grade inflammation. That inflammatory tone, sometimes called inflammaging, is associated with muscle breakdown. A well-functioning gut ecosystem may help keep this background inflammation in check, indirectly supporting muscle maintenance.

Where urolithin A fits in the axis

Urolithin A is one of the clearest real-world examples of the gut-muscle axis in action, because the compound itself is made by gut bacteria. When you eat ellagitannins, found in pomegranates, walnuts, and certain berries, specific gut microbes can convert them into urolithin A. Here is the catch that makes the axis so tangible: only some people carry the microbes needed to produce meaningful amounts. Two people can eat the same pomegranate and end up with very different urolithin A levels, purely because of who lives in their gut. That variability is a large part of why a standardized supplement exists.

Once produced, urolithin A is studied for supporting mitophagy, the process cells use to recycle worn-out mitochondria, the energy structures that muscle relies on heavily. So the pathway runs gut to postbiotic to muscle mitochondria, a concrete illustration of gut chemistry reaching muscle biology.

The human evidence, kept separate from animal work, is meaningful but focused. A first-in-human study by Andreux and colleagues (Nature Metabolism, 2019) found urolithin A safe and well tolerated up to 1,000 mg per day and produced a mitochondrial gene-expression signature. Singh and colleagues (Cell Reports Medicine, 2022) tested 500 mg and 1,000 mg daily in middle-aged adults over four months and reported effects on muscle strength and exercise performance. Liu and D'Amico and colleagues (JAMA Network Open, 2022) studied older adults over roughly four months and reported improvements in muscle endurance. An eight-week randomized trial in the Journal of the International Society of Sports Nutrition (2024) examined resistance-trained men, and a 2025 trial in distance runners added to the exercise literature.

The preclinical foundation should be labeled as such. Ryu and colleagues (Nature Medicine, 2016) demonstrated mitophagy activation and improved muscle measures in rodents, along with extended lifespan in the worm C. elegans. A systematic review in Ageing Research Reviews (2024) summarized the field honestly: the human evidence is still emerging. In short, urolithin A supports a muscle-relevant maintenance process, and the strongest human signals so far involve strength and endurance, not the broader microbiome claims that are still being studied.

Practical ways to support the gut-muscle axis

The everyday levers are refreshingly simple. Eat plenty of fiber from varied plants to feed the bacteria that make short-chain fatty acids. Include fermented foods such as yogurt, kefir, and sauerkraut to add microbial diversity. Get adequate high-quality protein spread across the day to give muscle the raw materials it needs. And, crucially, train your muscles, resistance exercise is itself a signal that supports both muscle and, some research suggests, a healthier gut environment. These habits reinforce one another. A postbiotic like urolithin A is a targeted addition on top of that foundation, not a replacement for fiber, protein, or training.

Honest limitations

The gut-muscle axis is an exciting and active area, but it is still maturing. Much of the mechanistic detail comes from animal and cell studies, human trials are smaller and shorter, and causation versus correlation is not always resolved. A stronger microbiome is associated with better muscle outcomes, but that does not prove one produces the other. Treat the axis as a useful framework for good habits, not as a set of guarantees. For more depth, see our urolithin A guide, our page on urolithin A for muscle, and our list of foods high in urolithin A; if you are shopping, our roundup of the best urolithin A gummies lays out the options. This article is educational and is not a treatment for sarcopenia or any other condition; if you have concerns about muscle loss or gut health, talk with your doctor.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This guide is educational and is not a substitute for advice from a qualified healthcare provider.