Nearly one in seven people worldwide lives with a mental health disorder. But while treatments like therapy and medication help many, they don’t work for everyone, and access remains a major challenge. Now, researchers say the gut may hold new clues to improving mental well-being.
A team from the University of South Australia reviewed dozens of studies exploring the gut-brain connection and found growing evidence that gut microbes can directly influence brain chemistry, stress responses and even mood-related behaviors. Their review, published in Nature Mental Health, offers the strongest support yet that changes in the gut microbiome can play a causal role in mental health.
Lead author Srinivas Kamath, a PhD candidate at the University of South Australia, said the findings help explain why diet and lifestyle factors can have such powerful effects on how people feel.
“The gut–brain connection is one of the most exciting frontiers in mental health research,” Kamath said. “We already know that the trillions of microbes in our digestive system talk to the brain through chemical and neural pathways, affecting our mood, stress levels and even cognition.”
The review found that disrupted gut patterns are common in people with depression, anxiety and schizophrenia. Early clinical trials show that approaches such as probiotics, diet changes or fecal microbiota transplants can improve mood and anxiety in some patients. It also found that psychiatric medications can alter the microbiome, further demonstrating a two-way relationship between gut bacteria and mental health.
Co-author Dr. Paul Joyce said the next step is understanding which changes in gut bacteria drive those effects and how to use that knowledge to develop targeted therapies.
“If we can prove that gut bacteria play a direct role in mental illness, it could transform how we diagnose, treat, and even prevent these conditions,” Joyce said. “Microbiome-based therapies such as probiotics, prebiotics or tailored diets may offer accessible, safer, low-cost and culturally adaptable options that complement existing care.”
Globally, nearly 970 million people are affected by mental health disorders, and up to one-third don’t respond to standard treatments. The researchers say better understanding of the gut–brain axis could lead to more personalized and effective approaches, especially for those who don’t benefit from traditional medications.
Future studies will need to follow people over time and include more diverse populations to see how diet, environment and culture shape the gut microbiome and influence mental health. Joyce said large, long-term clinical trials are critical to determining whether microbiome therapies can deliver lasting results.
“Mental health doesn’t start and end in the brain,” Joyce said. “It’s a whole-body issue — and the gut may be the missing piece of the puzzle.”
This research was supported by the Hospital Research Foundation Group, the National Health and Medical Research Council of Australia, and international partners including the U.S. Department of Defense, the National Institutes of Health and Science Foundation Ireland.