You have probably experienced it without thinking twice about it. A heavy, greasy lunch that leaves you sluggish and irritable all afternoon. A nourishing breakfast that sets you up for a focused, productive morning. We instinctively know that food affects how we feel, but until recently, science could not fully explain why. That is changing rapidly, and the answers are coming from an unexpected place: your gut.
The emerging field of nutritional psychiatry is revealing that the connection between your digestive system and your brain is far more intimate, direct, and powerful than anyone previously imagined. Understanding this connection might be the single most important thing you can do for both your physical and mental health.
The Gut-Brain Axis: A Two-Way Highway
Your gut and brain are in constant communication through a network known as the gut-brain axis. The primary physical link is the vagus nerve, the longest cranial nerve in your body, which runs from your brainstem all the way down to your abdomen. Think of it as a high-speed data cable connecting your two most important organs.
But the communication is not one-directional. While your brain sends signals down to your gut (which is why stress can cause stomach problems), your gut sends an enormous volume of information back up to your brain. In fact, roughly 80 to 90 percent of the signals travelling along the vagus nerve go from the gut to the brain, not the other way around. Your gut is not just receiving instructions — it is actively shaping how you think and feel.
Your Gut: The Serotonin Factory
Here is a statistic that surprises nearly everyone who hears it: approximately 90 percent of your body's serotonin is produced in the gut, not the brain. Serotonin is the neurotransmitter most closely associated with feelings of wellbeing, happiness, and emotional stability. It also plays a critical role in regulating sleep, appetite, and pain perception.
The cells lining your gut produce serotonin in response to the food you eat and the signals from the bacteria living in your digestive tract. When your gut environment is healthy and well-nourished, serotonin production tends to be robust and well-regulated. When it is not, the effects ripple outward into your mood, your sleep, and your overall sense of wellbeing.
This is why the gut is often called the "second brain." It contains its own vast nervous system — the enteric nervous system — with over 500 million neurons. It operates with a degree of independence that no other organ system in the body can match.
The Microbiome: Trillions of Tiny Decision-Makers
Your gut is home to trillions of microorganisms collectively known as the gut microbiome. This ecosystem of bacteria, fungi, and other microbes weighs roughly two kilograms and contains more genetic material than your entire human genome. Far from being passive passengers, these organisms actively influence your health in profound ways.
Research has shown that the composition of your gut microbiome affects inflammation levels throughout your body, the production of neurotransmitters including serotonin and dopamine, your immune system function, how you metabolise food and extract nutrients, and even your stress response and resilience to anxiety. Studies in both animals and humans have demonstrated that transferring gut bacteria from an anxious individual to a calm one can actually transfer the anxious behaviour along with it. The microbiome is not just correlated with mental health — it appears to be causally involved.
Foods That Support Your Gut
The good news is that your gut microbiome is remarkably responsive to dietary changes. You can begin shifting its composition in a positive direction within days. Here are the food categories that research consistently shows support a healthy, diverse microbiome.
- Fermented foods like yoghurt, kefir, sauerkraut, kimchi, miso, and kombucha introduce beneficial live bacteria directly into your gut. Regular consumption of fermented foods has been linked to reduced inflammation and greater microbial diversity.
- High-fibre foods are the primary fuel source for beneficial gut bacteria. Vegetables, fruits, legumes, whole grains, nuts, and seeds all provide the prebiotic fibre that your microbiome needs to thrive. Aim for a wide variety rather than relying on a few favourites.
- Polyphenol-rich foods such as berries, dark chocolate, green tea, olive oil, and red cabbage provide plant compounds that beneficial gut bacteria love to feed on. Polyphenols also have direct anti-inflammatory effects.
- Omega-3 fatty acids found in oily fish like salmon, mackerel, and sardines help reduce gut inflammation and support the integrity of the gut lining, which is crucial for preventing harmful substances from leaking into the bloodstream.
Foods That Can Disrupt Gut Health
Just as certain foods nurture your microbiome, others can damage it. Understanding what to minimise is just as important as knowing what to eat more of.
- Ultra-processed foods — those with long ingredient lists full of additives, emulsifiers, and artificial sweeteners — have been shown to reduce microbial diversity and promote the growth of harmful bacterial strains. Emulsifiers in particular can damage the protective mucus layer lining your gut.
- Excess sugar feeds opportunistic bacteria and yeast at the expense of beneficial species. High sugar intake is associated with increased gut inflammation and a less diverse microbiome. This includes hidden sugars in sauces, cereals, and processed snacks.
- Excessive alcohol disrupts the gut barrier, promotes inflammation, and negatively alters the balance of gut bacteria. Even moderate drinking can have measurable effects on gut health.
Connecting Food to Feeling with Nourish
One of the most powerful things you can do for your gut-brain health is to start noticing the connection between what you eat and how you feel. The challenge is that these effects are often delayed by hours or even a day, making it difficult to spot patterns without a systematic approach.
This is where Nourish's health scoring system becomes genuinely valuable. By logging your meals through quick photo captures and rating your energy, mood, and digestion each day, Nourish builds a personalised picture of how your diet affects your wellbeing over time. You might discover that days with more fermented foods correlate with better mood scores, or that heavy processed food days are followed by poor sleep ratings.
These are not abstract scientific findings. They are patterns specific to your body, drawn from your data. That kind of personalised insight is what turns knowledge into lasting behaviour change.
Practical Steps to Improve Your Gut Health
You do not need to overhaul your entire diet overnight. Small, consistent changes compound remarkably over time. Here is where to start.
- Add one fermented food daily. A small pot of yoghurt with breakfast, a spoonful of sauerkraut with lunch, or a glass of kefir in the afternoon. Consistency matters more than quantity.
- Aim for 30 different plant foods per week. This includes fruits, vegetables, grains, legumes, nuts, seeds, herbs, and spices. Diversity in your diet drives diversity in your microbiome.
- Reduce ultra-processed food gradually. Swap one processed snack for a whole food alternative each week. Over a month, the cumulative effect is significant.
- Track the connection. Use Nourish to log your meals and rate how you feel. After two to three weeks, review your patterns. The insights might surprise you.
- Be patient. Your microbiome did not develop overnight and it will not transform overnight either. Give dietary changes at least four to six weeks before evaluating their impact on your mood and energy.
The Bigger Picture
The gut-brain connection represents a fundamental shift in how we understand mental health and wellbeing. It tells us that what we eat is not just about weight or physical health — it is about how we think, feel, and experience the world. Every meal is an opportunity to support or undermine that connection.
The science is clear, and it is only getting clearer. Taking care of your gut is one of the most effective things you can do for your mind. And with tools like Nourish that make it easy to see the connection in your own life, there has never been a better time to start paying attention to what is on your plate.