The Gut-Brain Axis: What It Actually Means

The gut and the brain are in constant conversation. They communicate through a network of nerves, hormones, and immune signals in what scientists call the gut-brain axis. This isn’t a metaphor. There is a literal two-way communication channel, most notably the vagus nerve, running between the digestive system and the brain. What happens in one affects the other, in both directions.

Here’s the fact that tends to stop people in their tracks: an estimated 90% of the body’s serotonin is produced in the gut, not in the brain. Serotonin is the neurotransmitter most associated with mood regulation, emotional stability, and that general sense of being okay. We think of it as a brain chemical, but the gut is its primary production site, and the bacteria living in the gut play a direct role in how much gets made.

This means the health of our gut microbiome, the trillions of bacteria, fungi and other microorganisms living in our digestive tract, is not just a digestion issue. It’s a mental health issue.

What Probiotics Have to Do With It

Probiotics are live bacteria that, when present in sufficient amounts, support the health of our gut microbiome. The bacteria most studied in relation to mood are from the Lactobacillus and Bifidobacterium families. These are the same strains found naturally in fermented dairy, including dahi.

Researchers at the University of Virginia have spent years studying exactly how Lactobacillus influences mental health. What they found is that this bacteria helps the body manage stress by regulating a metabolite called kynurenine, which, when elevated, has been directly linked to driving depression. When Lactobacillus levels in the gut dropped, kynurenine went up, and depression symptoms followed. When Lactobacillus was restored, mood improved.

A 2025 review published in Frontiers in Pharmacology found that probiotic supplementation significantly reduced depressive symptoms across multiple studies, with effects mediated through the regulation of serotonin, GABA (another calming neurotransmitter), and the body’s stress hormone system. A separate meta-analysis of 1,401 participants found that probiotics produced meaningful reductions in both depressive symptoms and anxiety.

These are not fringe findings. This research is happening at serious institutions and being published in peer-reviewed journals. The gut-mood connection is real, measurable, and growing in clinical relevance.

So What Makes Dahi Different from a Supplement?

A lot, actually.

First, dahi made at home is a living food. Each household’s culture is unique, shaped by the local environment, the water, the temperature, the starter passed down from a previous batch. As one food science researcher noted in a discussion of Indian fermented foods, every household’s curd has a distinct microbial fingerprint because of the specific conditions it’s made in. This diversity of bacterial strains may be more beneficial than a single-strain supplement precisely because the gut microbiome thrives on variety.

Second, dahi has been a daily food for most South Asian households across generations, not a therapeutic dose taken occasionally. The consistent, low-level intake of live bacteria through food is exactly the kind of sustained gut support that researchers say matters most. One bowl of dahi won’t rewire our microbiome. Years of eating it as part of a varied, fibre-rich diet very likely will.

Third, unlike many probiotic supplements, dahi comes bundled with protein, calcium, and fat, all of which support absorption and overall gut health in ways that an isolated capsule doesn’t replicate.

The Stress Connection for South Asian Communities

This is worth sitting with for a moment.

Research on the gut-brain axis shows that chronic psychological stress directly disrupts the gut microbiome. It reduces Lactobacillus levels, increases gut permeability, and triggers inflammatory responses that feed back into the brain and worsen mood. The gut and the mind spiral together.

South Asian communities carry particular stressors: the pressures of migration, intergenerational expectations, cultural identity navigation, the unspoken weight of family obligations, and communities where mental health struggles are still often absorbed quietly rather than addressed openly. Chronic stress is not incidental for many of us. It is structural.

What this means biologically is that our gut microbiomes may be more depleted than we realise, not because of poor diet, but because of the sustained stress load many of us carry. Supporting the gut through fermented food is not a cure for any of this. But it is a consistent, low-barrier form of care that works with the body’s own systems rather than against them.

A Few Things Worth Knowing

Store-bought vs homemade.

Commercial dahi is often heat-treated after fermentation to extend shelf life, which kills most of the live bacteria. Homemade dahi, set fresh with a live starter, retains far more active probiotics. If making it at home isn’t practical, look for labels that say “contains live and active cultures.”

Chaas and lassi count too.

Diluting dahi into chaas or lassi doesn’t destroy the bacteria. Both are excellent ways to get probiotic benefit, particularly chaas with a tadka of mustard seeds, curry leaves, and a pinch of hing, a combination that also supports digestion through its own properties.

Fermentation time matters.

Longer-fermented dahi (slightly more sour) generally contains a higher bacterial count. The mild, fresh dahi many of us prefer is still beneficial, just less potent than a longer-set batch.

Consistency over quantity.

A small amount of dahi daily, as part of a meal, is more meaningful for gut health than large amounts occasionally. This is, conveniently, exactly how South Asian food culture has always used it.

The Bigger Picture

There is something worth naming in all of this. For generations, South Asian families have been told, often implicitly, that our traditional food practices needed to be upgraded, that wellness looked like expensive supplements, green juices, and imported probiotics. The gut health industry is now worth billions globally, selling back to us, in capsule form, a fraction of what our dahi has contained all along.

None of this means dahi is a treatment for depression or anxiety. Mental health is complex, and food is one piece of a much larger picture that includes rest, relationships, reduced stigma, professional support, and the kinds of structural changes that allow people to actually feel safe and supported in their lives.

But it does mean that the bowl of dahi our nani placed on the table every day, made fresh, eaten with rice and pickle and a little love, was doing something real. And that’s worth knowing.

If we’re thinking about mental wellbeing in a more holistic way and want support that actually understands our cultural context, we’re at Sukoon Cares.