The brain and the gut
The brain and the gut
Medically reviewed by:
Dr John Freeman
The brain and the gut are in constant communication, and scientific understanding of this relationship continues to grow rapidly. This two-way communication system is known as the gut–brain axis, and it plays a critical role in both mental and physical health.
The gut–brain connection and mental health
Many mood disorders, including anxiety and depression, are now well established to have links with functional gastrointestinal disturbances. Research also shows that diet and the gut microbiome can influence cognitive function, mood, and behaviour.
Animal studies illustrate this powerfully. In laboratory experiments, researchers have been able to make inactive, anxious rats more active and resilient simply by altering their gut bacteria. Conversely, transferring gut bacteria from depressed rats into healthy ones can induce low-mood and withdrawn behaviours. These findings highlight the profound influence gut microbes can have on brain function.
How the gut talks to the brain
The gut–brain axis transmits information primarily through the vagus nerve, a major nerve connecting the digestive system to the brain. This pathway helps translate what happens in the gut into signals that affect mood, motivation, and stress responses.
After food is eaten and digested, nutrients enter the small intestine, which is lined with millions of tiny finger-like structures called villi. Each villus is covered by a single layer of cells known as the epithelium. These cells perform specialised functions such as absorption, immune defence, and communication.
Enteroendocrine cells: the gut’s sensory messengers
Among these cells are enteroendocrine cells, which act as sensors within the gut. Traditionally, these cells were thought to communicate only through hormones. However, recent discoveries have shown that some enteroendocrine cells also form direct synapse-like connections with nerves, including the vagus nerve. These specialised cells are known as neuropod cells.
Neuropod cells can detect mechanical, thermal, and chemical signals—such as nutrients and bacterial by-products—within the gut lumen. They convert this information into tiny electrical signals.
From gut to brain in seconds
These electrical impulses are transmitted via synapses onto neurons of the vagus nerve. The vagal neurons then carry this sensory information directly to the brainstem, effectively linking events in the small intestine to brain activity.
Remarkably, this pathway allows food-related signals from the gut to influence brain function within seconds, not minutes or hours as previously believed.
Implications for health and disease
While this rapid communication system helps regulate appetite, mood, and stress, it may also provide a pathway through which gut inflammation or pathogenic signals can influence brain function. This is particularly relevant in conditions involving gut dysbiosis, such as IBS or SIBO.
Why this matters
Understanding the gut–brain axis provides a foundation for developing new therapies aimed at disorders involving altered gut–brain signalling. These insights are reshaping how we approach conditions ranging from digestive disorders to anxiety, depression, and cognitive health.
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