If you’ve spent any time on wellness social media lately, you’ve probably seen the claims. Your gut is your second brain. Fix your gut and you’ll fix your anxiety. Probiotics are the new antidepressants.

Some of this is grounded in real science. Some of it is marketing. And telling the difference matters, because people are making real health decisions based on what they see in a 60-second reel.

So let’s sort through what we actually know about the gut-brain connection — and where the evidence gets thin.

The Basics: What Is the Gut-Brain Axis?

Your gut and your brain communicate constantly through a network of nerves, hormones, and immune signals. The main highway is the vagus nerve, which runs from your brainstem to your abdomen and carries information in both directions.

Your gut also houses a huge population of microorganisms — collectively called the gut microbiome — that influence everything from digestion to immune function. There are roughly 38 trillion bacteria in your gut, and the composition of that community affects how your body works.

This isn’t new science. Researchers have been studying the gut-brain axis for decades. What’s changed in the past 10 years is our ability to map the microbiome in detail and study how it interacts with brain function.

What the Evidence Supports

Gut health affects mood. There’s solid evidence that the gut microbiome influences the production of neurotransmitters like serotonin. In fact, about 95 percent of your body’s serotonin is produced in the gut, not the brain. Changes in gut bacteria composition have been linked to changes in mood and anxiety levels in both animal and human studies.

Diet affects your microbiome. What you eat directly shapes the diversity and composition of your gut bacteria. Diets high in fibre, fermented foods, and varied plant foods tend to support a more diverse microbiome. Diets high in ultra-processed foods tend to reduce diversity. A landmark study from researchers at Deakin University here in Australia — the SMILES trial — found that a Mediterranean-style diet significantly reduced depression symptoms compared to a social support control group.

Stress affects your gut. Chronic stress can alter gut permeability (sometimes called “leaky gut”), change the composition of gut bacteria, and increase inflammation. If you’ve ever felt nauseous before a stressful event or had digestive issues during a difficult period, that’s the gut-brain axis at work.

Where the Hype Outpaces the Science

Specific probiotic strains for specific mental health conditions. This is where the marketing gets ahead of the research. While some studies have shown modest benefits from certain probiotics for anxiety and depression, the results are inconsistent across trials. We don’t yet have enough evidence to say “take this specific strain and your anxiety will improve.” Most probiotic supplements on the shelf haven’t been tested for mental health outcomes at all.

Gut health as a cure for mental illness. The gut-brain connection is real, but it’s one factor among many. Depression, anxiety, and other mental health conditions have genetic, social, psychological, and neurological components. Suggesting that someone can eat their way out of clinical depression is oversimplified and potentially harmful.

Microbiome testing kits. Several companies now offer at-home microbiome tests with personalised dietary recommendations. The problem is that we don’t yet know enough about what an “optimal” microbiome looks like. The science of microbiome testing is still in its early stages, and many researchers have expressed concern that these products over-promise and under-deliver.

What You Can Actually Do

If you want to support your gut health — and by extension, your mental wellbeing — the advice is honestly pretty straightforward:

Eat a variety of plant foods. Aim for 30 different plant foods per week. That includes fruits, vegetables, wholegrains, legumes, nuts, seeds, herbs, and spices. Diversity feeds diversity in your microbiome.

Include fermented foods. Yoghurt, kefir, kimchi, sauerkraut, miso, and kombucha all introduce beneficial bacteria. A Stanford study found that a diet high in fermented foods increased microbiome diversity and reduced markers of inflammation.

Reduce ultra-processed foods. You don’t need to eliminate them entirely, but making them a smaller portion of your overall diet supports better gut health. Think of it as crowding them out with whole foods rather than cutting them out with willpower.

Manage stress. Easier said than done, I know. But stress management isn’t separate from gut health — it’s part of it. Regular movement, adequate sleep, and practices like mindfulness or breathing exercises all support the gut-brain axis.

Be sceptical of expensive supplements. If someone is selling you a $90 probiotic with claims about curing your anxiety, ask for the evidence. Specifically, ask for peer-reviewed human trials. Not testimonials. Not animal studies. Human trials.

The Bottom Line

The gut-brain connection is real, fascinating, and worth paying attention to. But it’s not a magic fix, and anyone who tells you otherwise is probably selling something.

The best things you can do for your gut are the same things that are good for the rest of you: eat well, sleep enough, move your body, and manage your stress. Not glamorous advice, but it’s what the evidence supports.

And that’s always going to be more reliable than a trending supplement.