Could what you eat change your personality... and is the brain to blame for dictating our food choices - good and bad?

Is your evening meal having an effect on your personality? It might sound absurd, but the old idea, first popularised in the 19th century that 'you are what you eat' might be truer than we thought.

Psychologists and nutrition scientists are now piecing together evidence that our personalities may nudge us towards certain diets. And that what we eat could, in turn, be subtly shaping how we think, feel and interact.

We know that what you eat matters for brain health, so it stands to reason that your personality traits could be subtly shaped by your plate.

That evidence is still emerging – but what we do know now is that personality type can make healthy eating a breeze for some, and a battle for others.

A 2021 review in the journal Advances in Nutrition, which pulled together dozens of studies, showed there were clear links between personality and eating patterns.

Perhaps not surprisingly, people rated as more conscientious were most likely to eat healthily – with plenty of fruits, vegetables and wholegrains. Though if that conscientiousness slips into neuroticism (essentially, being more prone to anxiety, irritability or sadness), this was linked with emotional eating – and then consuming more sugary or high-fat foods.

Meanwhile, extroverts were found to eat more fruit and vegetables – but also more fast food and alcohol.

The researchers suggested this was because extroverts tend to be more sociable and sensation-seeking, so are often in situations where they eat a wider variety of foods – which could mean more fruit and veg at shared meals, but also more takeaways and alcohol when eating out or socialising.

It's thought that these patterns may be two-way, with what you eat also feeding back into the body, influencing the gut, your body's inflammation levels and even the brain.

And, in turn, emerging evidence suggests that this may affect your behaviour over time.

A striking example of this came from a 2002 study on prisoners, published in the British Journal of Psychiatry, where more than 230 young adult men were randomly given either a daily multivitamin and mineral supplement with omega-6 and omega-3 fatty acids, or a placebo.

Over the following five months, the number of disciplinary offences committed inside the prison by those taking the supplements was about 26 per cent lower.

The researchers thought this might be because the extra vitamins, minerals and fatty acids supported better brain function, helping with impulse control and decision-making. You could argue that we can't rely on the behaviour of prisoners to determine what would happen in the outside world, but other research now echoes such findings.

For example, people with lower levels of omega-3s (found in oily fish, such as salmon and mackerel, and walnuts) – especially a type called DHA – tend to show more signs of neuroticism and dwell more on their negative thoughts when feeling low, according to a 2018 study in the Journal of Psychosomatic Research.

So what is going on? One possible link is excess inflammation. Having a lot of low-grade inflammation in the body is linked with certain personality traits, according to a 2021 study in Brain, Behavior, and Immunity.

People who were more organised and disciplined (what psychologists call 'conscientious'), more curious and open to new ideas had lower levels of inflammation and did better on thinking and memory tests.

On the flip side, those who were more prone to worry or emotional ups and downs (traits linked with neuroticism) tended to have higher levels of inflammation and performed less well on these tests. We know that chronic inflammation can take its toll on how well the brain works.

A large UK study, published this year in the journal Nature, involving data from more than 160,000 people for over a decade, found that those who had more pro-inflammatory diets (with more ultra-processed food and less fruit and veg) had a higher risk of dementia, stroke, sleep disorders, anxiety and depression, while diets richer in fruit and vegetables (which are naturally anti-inflammatory) were linked with better brain health.

This is where the Mediterranean diet, for example – full of fruits, vegetables, wholegrains, nuts, seeds and oily fish (a good source of those omega fats) –could help, thanks to its anti-inflammatory effects.

Early research hints that our gut microbes could also be partly shaping our personality over time.

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People with a more diverse mix of gut bacteria – often a sign of a healthier gut microbiome – tended to have larger circles of friends, while people with less diverse microbiomes were more likely to feel stressed or anxious, according to research published in the Human Microbiome Journal in 2020.

Similarly, a study published in Brain, Behavior, and Immunity in 2018 found that people who were more open-minded and curious had more diverse gut microbiomes; people who were more prone to worry or less organised and disciplined had bacterial patterns that may be less healthy.

For now, it's hard to know if these differences in bacteria are simply consequences of having different diets, but research in mice hints that microbes may influence behaviour.

For example, a 2021 study of mice, published in the journal Nature, found that those with different gut bacteria behaved differently – some were more confident and others more anxious or withdrawn.

When the gut bacteria from the anxious mice were given to germ-free mice, those mice started acting anxiously, too. The anxious mice also had more inflammation in their body fat and changes in metabolism, which the researchers think may send signals to the brain and affect how they act.

Though in reality it will not be the bacteria directly, but their by-products that may nudge our mood and stress responses – and in doing so, perhaps make certain aspects of our personality more or less pronounced.

There is much that scientists have yet to understand in this area, but if diet can influence something as immediate as our mood, energy levels and focus, it's not too far a stretch to imagine that, over time, it also shapes how we feel and interact with the world.