If someone had told me five years ago that the bacteria in my gut were influencing my mood, I’d have smiled politely and backed away slowly. It sounded like the kind of thing you’d hear at a wellness expo between the crystal healing booth and the raw cacao stand.

But the science has caught up, and it’s compelling. Australian researchers, in particular, are at the forefront of understanding the gut-brain axis — and what they’re finding is reshaping how we think about mental health treatment.

What Is the Gut-Brain Axis?

In simple terms, your gut and your brain are in constant two-way communication. They talk to each other via the vagus nerve, through immune system signalling, and through the chemicals produced by the trillions of microorganisms living in your digestive tract — your gut microbiome.

Those microorganisms produce neurotransmitters. Roughly 90% of your body’s serotonin — the neurotransmitter most associated with mood regulation — is produced in the gut, not the brain. Your gut bacteria also produce gamma-aminobutyric acid (GABA), dopamine, and other compounds that directly influence how you feel.

When the composition of your microbiome is disrupted — through poor diet, antibiotics, stress, or illness — it can affect these chemical signals. And increasingly, research is showing that this disruption is linked to conditions including depression, anxiety, and even cognitive decline.

The Australian Research Making Waves

Australia has become something of a global hub for gut-brain research, and a few studies stand out.

The SMILES Trial from Deakin University, led by Professor Felice Jacka, was one of the first randomised controlled trials to show that dietary improvement could treat depression. Participants with moderate to severe depression who followed a modified Mediterranean diet for 12 weeks showed significantly greater improvement than a control group receiving social support. About a third of the dietary group achieved remission.

That was published back in 2017, but it kicked off a wave of research that continues to produce results.

More recently, researchers at the University of Melbourne have been investigating specific bacterial strains and their relationship to depressive symptoms. Their 2025 paper in Molecular Psychiatry identified particular microbiome signatures that were consistently different in people with treatment-resistant depression compared to healthy controls.

CSIRO’s ongoing gut health research has also contributed valuable population-level data on Australian dietary patterns and microbiome diversity. Their findings suggest that Australians who eat fewer than 20 different plant foods per week have significantly less diverse microbiomes — and lower diversity is consistently associated with poorer mental health outcomes.

What This Means in Practical Terms

I want to be clear about something: this research doesn’t mean you can eat your way out of clinical depression. Mental health is complex, and diet is one factor among many, including genetics, life circumstances, trauma, sleep, and social connection.

But what the research does suggest is that what you eat matters more for your mental health than we previously appreciated. And for many people, dietary changes can be a meaningful part of a broader mental health strategy.

Here’s what the evidence supports:

Diversity is king. Aim for 30 different plant foods per week. That sounds like a lot, but it includes fruits, vegetables, nuts, seeds, legumes, whole grains, herbs, and spices. A stir-fry with five different vegetables, some cashews, and a few spices gets you halfway there in one meal.

Fibre feeds your good bacteria. Your beneficial gut bacteria thrive on dietary fibre — particularly prebiotic fibres found in foods like onions, garlic, leeks, asparagus, bananas, oats, and legumes. Most Australians eat well below the recommended 25-30 grams of fibre per day.

Fermented foods add beneficial microbes. Yoghurt, kefir, sauerkraut, kimchi, miso, and kombucha all contain live cultures that can support microbiome health. A Stanford study found that a diet high in fermented foods increased microbiome diversity and reduced markers of inflammation after just ten weeks.

Ultra-processed foods appear to do harm. A 2025 Lancet meta-analysis found consistent associations between high ultra-processed food consumption and increased risk of depression and anxiety. The mechanisms likely involve inflammation, blood sugar dysregulation, and negative effects on microbiome composition.

The Tech Angle

This is an area where technology is starting to play an interesting role. Several Australian startups are now offering microbiome testing — you send in a stool sample and receive a report on your bacterial composition along with dietary recommendations.

Some healthcare providers and workplace wellness programs are incorporating this kind of personalised data into their mental health offerings. Companies working with AI consultants Brisbane and similar firms are exploring how to use health data responsibly to inform employee wellbeing initiatives, including nutritional support.

It’s early days, and I’d encourage healthy scepticism about any test that claims to diagnose mental health conditions based on a stool sample alone. But as a tool for understanding your individual gut health and guiding dietary choices? The technology is getting genuinely useful.

My Personal Take

I started paying more attention to my gut health about 18 months ago, not because I was depressed, but because I was curious. I increased my plant diversity, added more fermented foods, and cut back on the ultra-processed stuff that had crept into my diet during a busy period.

Did I notice a difference? Honestly, yes. My energy was more stable. My mood felt less reactive. My digestion improved noticeably. But I also changed my sleep habits and exercise routine around the same time, so I can’t isolate the dietary effect.

That’s the messy reality of wellness: everything is connected. But the growing body of Australian research gives us good reason to take the food-mood connection seriously — not as a replacement for other mental health support, but as a foundation that makes everything else work a little better.

Your gut is talking to your brain. It’s worth making sure it has good things to say.

For evidence-based dietary guidance, consider seeing an Accredited Practising Dietitian. You can find one near you through the Dietitians Australia website.