Most of us are familiar with the idea that food affects our physical health. We know that what we eat can influence our energy levels, our fitness, our heart health and our risk of developing conditions such as type 2 diabetes and certain cancers.
But what about our mental health? If food can affect our muscles, bones, blood vessels and immune system, why wouldn’t it affect our brain? After all, the brain is just another organ.
Over the past decade, scientists have become increasingly interested in a field known as nutritional psychiatry – the study of how diet influences mental health and wellbeing.
What began as an intriguing theory has developed into a rapidly growing area of research. Studies are now showing that what we eat may influence not only our physical health, but also how we think, feel and function day to day. One study found that people who ate more fruit and vegetables reported greater wellbeing and life satisfaction (1). Another found that participants following a Mediterranean-style dietary pattern experienced significant improvements in symptoms of depression, with benefits still present six months after the intervention ended (2).
Then came the landmark SMILES trial, the first randomised controlled trial to demonstrate a causal link between dietary improvement and depression (3). In the study, adults with major depression were randomly assigned to either receive dietary support or social support for 12 weeks. By the end of the trial, 32% of those in the dietary intervention group were no longer considered depressed, compared with just 8% of those receiving social support alone.
Since then, multiple reviews and meta-analyses have strengthened the evidence, suggesting that improving diet quality can help reduce symptoms of depression and support overall mental wellbeing (4).
But take note – this doesn’t mean that depression can be cured by eating more vegetables. Mental health is complex. Genetics, hormones, sleep, social support, life experiences, financial circumstances and physical health all play important roles.
But… nutrition appears to be one piece of the puzzle that we may have underestimated for far too long.
The relationship between food and mood is fascinating because there isn’t just one pathway involved.
The food we eat influences our brain through a network of systems involving our gut microbiome, immune system, hormones, blood vessels and nervous system. Scientists are still uncovering exactly how these systems interact, but several mechanisms have emerged as particularly important.
Perhaps the most exciting area of research is the gut-brain axis. This refers to the two-way communication system between your digestive system and your brain.
Inside your digestive tract live trillions of bacteria, fungi and other microbes collectively known as the gut microbiome. Far from simply helping us digest food, these microbes communicate with our brain through nerves, hormones, immune signals and chemical messengers. Researchers now recognise the gut microbiome as an important regulator of brain function and mental wellbeing (5). And one of the biggest influences on the gut microbiome?
The food we eat.
When beneficial gut bacteria ferment fibre from plant foods, they produce compounds known as short-chain fatty acids. These compounds help maintain the gut lining, support immune function, regulate inflammation and may influence brain health. Researchers are increasingly investigating their role in depression and other mental health conditions (5,6).
This is one reason why plant foods appear so consistently in studies of positive health outcomes. Vegetables, fruits, beans, lentils, peas, wholegrains, nuts and seeds all provide fibre that beneficial gut bacteria thrive on.
One of my favourite ways to think about fibre is that we’re not just feeding ourselves – we’re feeding the trillions of microbes that live alongside us.
Another important piece of the puzzle is inflammation.
Inflammation is a normal and essential part of the immune response. However, when inflammation becomes chronic and persistent, it may influence mood and brain function.
Researchers have observed higher levels of inflammatory markers in many people experiencing depression.
Plant-rich dietary patterns naturally provide antioxidants and anti-inflammatory compounds, including polyphenols found in colourful fruits, vegetables, herbs, spices, tea, coffee, cocoa, nuts and seeds.
The Mediterranean dietary pattern, which has shown some of the strongest evidence for supporting mental health, is thought to work partly through these anti-inflammatory effects (7).
Your brain is an energy-hungry organ. Although it makes up only around 2% of body weight, it uses roughly 20% of the body’s energy supply.
Meals rich in fibre, healthy fats and plant proteins help provide a slower, steadier release of energy compared with highly refined foods. Most of us have experienced the energy crash that can follow a meal that causes blood sugar to rise and fall rapidly.
Whilst blood sugar isn’t the sole driver of mood, maintaining more stable energy levels throughout the day may support concentration, resilience and emotional wellbeing.
One of the more intriguing areas of research suggests that our gut microbes may even influence food preferences and eating behaviours. Yes, really.
The science is still evolving, but some researchers believe that certain microbes may affect signalling pathways involved in appetite, cravings and reward.
Whilst there is still much to learn, it highlights just how interconnected our gut, brain and food choices really are.
Of course, humans are wonderfully complicated. The relationship between nutrition and mental health is rarely straightforward.
People living in more deprived communities often face greater barriers to accessing healthy food, including cost, availability, time and cooking facilities. These same communities frequently experience higher rates of poor physical and mental health. Mental health conditions themselves can also make shopping, cooking and eating well more difficult.
This means that diet both influences, and is influenced by, mental health.
This is one reason why conversations about food and mood should always be compassionate and realistic.
What I love about this research is that it doesn’t point us towards expensive supplements, detoxes or superfoods. Instead, many of the foods associated with better mental wellbeing are the same humble foods that support our physical health too.
If you’d like to experiment with some of the findings from nutritional psychiatry, here are a few evidence-based ideas:
One of the strongest predictors of a diverse gut microbiome is dietary diversity.
In the American Gut Project, people who ate more than 30 different plant foods each week had significantly more diverse gut microbiomes than those eating fewer than 10. Diversity matters because different microbes thrive on different fibres and plant compounds.
Remember that herbs, spices, beans, nuts, seeds and whole grains all count.
Legumes are among the richest sources of fermentable fibre, helping beneficial bacteria produce short-chain fatty acids.
A serving might look like:
Berries contain polyphenols, natural plant compounds that appear to benefit both gut microbes and brain health.
A handful (around 80g) of blueberries, blackberries, raspberries or mixed berries is enough to make a meaningful contribution.
Frozen berries work just as well.
Ground flaxseed provides fibre alongside plant omega-3 fats.
Omega-3 fatty acids have been studied extensively in relation to brain health and mood.
One tablespoon stirred into porridge, yoghurt or a smoothie is an easy starting point. Keep them in the fridge to preserve the healthy fats.
Many herbs and spices are surprisingly rich in polyphenols.
Rather than thinking of them as garnishes, use them generously.
Parsley, coriander, rosemary, mint, oregano, cinnamon and turmeric all contribute compounds that your gut microbes can use.
Tea, coffee and cocoa are among the largest sources of polyphenols in many diets.
For most people, moderate intakes can contribute positively to overall polyphenol intake.
You don’t need a perfect diet. Small changes repeated consistently often have the greatest impact.
The science is still evolving, but the message is becoming increasingly clear:
Food doesn’t just shape our physical health. It helps shape the environment in which our brain operates. And whilst no single meal will transform our mental health overnight, the choices we make day after day may be more powerful than we once realised.
If you have concerns regarding your mental health, always seek support from an appropriate healthcare professional. You could start by speaking to your GP, visiting a mental health charity such as Mind, or finding local support through organisations such as Hub of Hope.
Don’t forget to do something that makes you smile today.
Rosie x
Written by Rosemary Martin RD 2021. Updated 2026.
If you’re looking for more, why not join our very popular FREE Masterclass – The 3 Secrets to Banish Cravings and Lose Weight on a Plant-Based Diet. Just choose the next date and time that suits you and we will see you there!
You also can contact me directly at hello@rosemarynutrition.co.uk or follow me on Instagram at @plantdietitianrosie.
