The gut-brain connection | How what you eat shapes how you think and feel

Most people understand that food affects the body. Eat well and you have more energy. Eat poorly and you feel sluggish. But the relationship between what you eat and how you feel goes much deeper than energy levels. It reaches into mood, cognition, stress response, and the way the nervous system operates day to day. The gut is not simply a digestive organ. It is a communication system. And the signals it sends upward, to the brain, are constant, influential, and surprisingly easy to support or disrupt through the choices made at every meal.

The second brain

The gut contains what scientists refer to as the enteric nervous system - a vast network of around 500 million neurons lining the gastrointestinal tract. This network operates largely independently of the brain. It regulates digestion, responds to stress, and communicates bidirectionally with the central nervous system via the vagus nerve.

This connection is why the gut is sometimes called the second brain. Not as a metaphor, but as a description of function. The gut does not just receive instructions from the brain. It sends them. Estimates suggest that roughly 90% of the signals travelling along the vagus nerve move upward, from gut to brain, rather than the other direction. What this means in practice is that the state of the gut has a direct and ongoing influence on mood, cognition, and emotional regulation.

The microbiome and its role in how you feel

The gut microbiome, AKA the community of trillions of bacteria, fungi, and other microorganisms living in the digestive tract, plays a central role in this gut-brain dialogue.

A diverse, balanced microbiome supports the production of neurotransmitters and signalling molecules that influence how we feel. Serotonin is the most well-known example. Despite being associated primarily with mood and mental health, around 90% of the body's serotonin is produced in the gut, not the brain. The bacteria in the digestive tract contribute directly to this production.

GABA, the brain's primary calming neurotransmitter, is also produced in part by gut bacteria. Short-chain fatty acids, produced when gut bacteria ferment dietary fibre, influence inflammation levels, brain function, and even the integrity of the blood-brain barrier.

When the microbiome is disrupted, through poor diet, antibiotics, chronic stress, or lack of dietary diversity, these processes are affected. The downstream effects can include low mood, anxiety, brain fog, and increased stress reactivity. Often, the connection to the gut is not considered.

How stress disrupts the gut-brain connection, and the gut disrupts stress

The relationship between the gut and stress runs in both directions. Chronic stress alters gut motility, reduces the diversity of the microbiome, and increases intestinal permeability, sometimes referred to as leaky gut. This allows bacterial products to enter the bloodstream, triggering systemic inflammation that can affect brain function and mood.

At the same time, a disrupted gut amplifies the stress response. Inflammation in the gut signals threat to the brain. The nervous system responds accordingly, maintaining a higher baseline of activation than the external situation might warrant.

This loop is important to understand. It means that addressing gut health is not only about digestion. It is about creating conditions in which the nervous system can genuinely settle... something that is difficult to achieve if the signals arriving from the gut are consistently ones of disruption.

What supports a healthy gut-brain connection

The good news is that the microbiome is responsive. It shifts with dietary changes more quickly than most people expect. Meaningful changes in microbial diversity have been observed within days of dietary adjustment.

Prioritise fibre from varied sources. Gut bacteria feed on dietary fibre, and they are specific in their preferences. Different bacterial strains thrive on different types. A diet that includes a wide range of vegetables, legumes, wholegrains, nuts, and seeds provides the variety the microbiome needs. A useful rough target, though not a rule, is 30 different plant foods across the week.

Include fermented foods. Foods like natural yoghurt, kefir, sauerkraut, kimchi, miso, and kombucha introduce live bacteria to the gut. Research suggests that regular consumption of fermented foods increases microbial diversity and reduces markers of inflammation, including in the brain.

Reduce ultra-processed food. Highly processed foods tend to be low in fibre, high in emulsifiers and additives, and disruptive to gut lining integrity. Their regular consumption is associated with reduced microbiome diversity and increased inflammatory signalling. This does not require perfection or elimination. But reducing their frequency matters.

Manage stress as part of gut health. Because the relationship runs in both directions, practices that down-regulate the nervous system also support gut function. Breathwork, cold and heat exposure, adequate sleep, and time spent in genuinely restorative environments all reduce the stress signals that disrupt the gut-brain axis.

Eat with some regularity. The gut operates on rhythms aligned with the body's circadian system. Erratic meal timing, particularly eating late at night, disrupts these rhythms and affects both digestive function and the microbial community.

Stay hydrated. Water is fundamental to gut motility and the mucosal lining that protects the gut wall. Chronic mild dehydration is underestimated as a contributor to digestive sluggishness and the low-grade fatigue that follows.

The mood connection in practice

The influence of the gut on mood is not abstract. People who improve their diet consistently report not only physical changes but psychological ones. This means a steadier emotional baseline, reduced anxiety, improved focus, and a sense of ease that is difficult to attribute to any single factor.

This does not mean food is a substitute for mental health support where that is needed. But it does mean that the gut is a legitimate and often overlooked lever in how we feel from day to day.

When the microbiome is supported, serotonin production improves. Inflammation decreases. The vagus nerve carries steadier, less alarming signals upward. The nervous system has less to manage. Mood becomes more stable — not through intervention, but through removing a source of disruption that was present all along.

Wellness conversations often separate body and mind. Eat well for your body. Manage stress for your mind. But the gut-brain connection does not recognise that boundary. What you eat shapes the environment in which your nervous system operates. And a nervous system that is well supported, from the gut upward, is one that can respond to life's demands without being overwhelmed by them.

The food on your plate is not only fuel. It is information. And the gut is always listening.

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Speak soon,

The ISKA Team