It is quiet, yet it never falls silent. BORAY has spent a long time learning to listen to this channel — science calls it the gut-brain axis. We would like to explain it clearly, and honestly.
A two-way channel between gut and brain, with both ends always answering the other.
The gut-brain axis is an ongoing, two-way network of communication between the gut and the central nervous system. What the brain feels reaches the gut, and the gut's own signals travel back up to the brain. This conversation unfolds through several routes at once — nerves, hormones, the immune system, metabolism — like parallel lines that echo one another.
In recent years, research has paid growing attention to the vast community of microbes living in the gut, the gut microbiome, and its part in all of this — which is why the field often prefers the fuller name, the microbiota-gut-brain axis. In fairness, this remains an unfolding area of science: many mechanisms are clearer in animal studies, while in humans the evidence is still largely one of association and early findings. It cannot stand in for the diagnosis or treatment of any condition.
The vagus nerve is the main neural channel connecting gut and brain. Roughly eighty percent of its fibres carry information upward, from the gut to the brain, which is how the mind can sense the gut's state. Research suggests it also takes part in regulating local inflammation and gut permeability — and that stress may quiet its activity.
As gut bacteria ferment dietary fibre, they produce metabolites such as short-chain fatty acids. Research suggests these molecules are associated with immune regulation, the gut barrier, and signalling linked to the blood-brain barrier — a kind of chemical language the microbiome uses to reach the wider body. Their precise cause and meaning are still being studied.
Most of the body's serotonin — often cited at around 90–95% — is made not in the brain but in the gut, where it helps regulate the gut's own functions. One important boundary of the science: gut-derived serotonin largely cannot cross the blood-brain barrier. Gut and brain are, in truth, two relatively separate pools, and cannot simply be equated.
The HPA axis is the body's central stress-response system, regulating how we answer pressure through hormones such as cortisol. Research suggests the state of the gut microbiome is associated with this axis; in one small study of healthy adults, a specific strain was associated with lower cortisol after stress — an early finding, not a general conclusion.
Research suggests the state of the gut microbiome may be associated with mood; some dietary or probiotic approaches have shown positive shifts in mood measures within certain human trials. Yet the evidence as a whole remains limited and inconsistent, and effects often vary by strain and by person. We say only that research suggests a possible link — and promise nothing.
Sleep, the gut microbiome and the stress axis are interrelated. In the small study mentioned above, participants reported an improvement in how their sleep felt, while objectively measured sleep showed no significant difference. We prefer to keep these two honest and apart — what is felt, and what is measured, are not the same thing.
The link between the gut-brain axis and cognition is an active area of research, touching metabolites, immunity and the blood-brain barrier. For now, most of it rests on association and mechanism rather than proof. We would rather put it plainly — the field is still exploring a potential connection.
Some things are reasonably established: the gut and brain do speak both ways, and the vagus nerve, immunity, hormones and microbial metabolites are real physiological pathways. Much remains under study: in healthy people, how far and by which route changing the microbiome can steadily shape mood, sleep and focus — the causal evidence is still thin. We believe that something making sense in principle is not the same as being shown in people, and that naming that distance openly earns more trust than overstating it. So we choose words like research suggests, is associated with, is being explored — and we say them slowly, and carefully.
If this conversation between gut and mind leaves you curious, we would be glad to share more — about the way we research, and about how we work.