Nearly one in seven people live with a mental health disorder, making it one of the world's most pressing health challenges. Yet despite available treatments, most people still lack access to effective care.
Now, researchers from the University of South Australia are exploring the connections between the gut and the brain to decipher their role in mental health and wellbeing.
Examining the growing evidence that the gut and the brain are deeply connected, their review presents the strongest proof yet that changes in a person's gut microbiome can directly affect their brain chemistry.
The review found:
- Strong causal evidence that gut microbes can change brain chemistry, stress responses and behaviours in animal models.
- Disrupted gut patterns in conditions like depression and schizophrenia.
- Early trials of probiotics, diet changes, and faecal microbiota transplants improve mood and anxiety.
- Psychiatric medications can change the microbiome, demonstrating the gut-brain connection.
Lead author and PhD candidate, UniSA's Srinivas Kamath, says the gut could hold the key to improving mental health worldwide.
"The gut-brain connection is one of the most exciting frontiers in mental health research," says Kamath.
"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.
"But the big question is whether changes in gut bacteria actually drive mental illness or mirror what's happening elsewhere in the body."
Globally, mental health disorders affect nearly 970 million people, with depression and anxiety ranking among the leading causes of disability. Yet up to one-third of patients do not respond to current medications or therapies, highlighting the need for new and accessible treatments.
"There's a growing awareness that lifestyle factors such as diet, stress, and environment can shape both gut bacteria and mental wellbeing," says co-researcher Dr Paul Joyce.
"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.
"Microbiome-based therapies such as probiotics, prebiotics or tailored diets may offer accessible, safer, low-cost and culturally adaptable options that complement existing care."
The researchers say future studies must track gut changes over time and include more diverse, larger populations, to better understand how diet, environment and culture shape the gut-brain connection.
"Clinical trials should move beyond small, short-term studies and instead test whether microbiome-based therapies can deliver lasting benefits, especially when combined with existing treatments," Dr Joyce says.
"By unlocking the gut's role in mental health, we can develop practical, scalable tools for prevention and care, giving clinicians and patients new options to manage wellbeing.
"Mental health doesn't start and end in the brain. It's a whole-body issue - and the gut may be the missing piece of the puzzle."
