The phrase ‘You are what you eat’ derives from a pioneering French food critic who, 200 years ago, published a bestseller titled The Physiology Of Taste.
Jean Anthelme Brillat-Savarin, who was a gourmet, scientist and politician, famously declared in 1825: ‘Tell me what you eat and I will tell you who you are.’
Now researchers are developing Brillat-Savarin’s idea into a potentially life-changing science based on the belief that our food actually drives our mood – this pioneering approach, called nutritional psychiatry, aims to offer effective new dietary-based treatments for conditions such as depression, anxiety and bipolar disorder.
Two British scientists are leading the research into this area after finding that changing their diets improved their own mental health conditions.
At the University of Oxford, Ally Houston, a psychology doctorate student, says dietary change has helped him manage his ADHD and depression, while at the University of Edinburgh, Dr Iain Campbell, a research fellow in metabolic psychiatry, has used dietary changes to help control his bipolar disorder (more of which later).
Such is the interest in this new field that a unique multi-million-pound science hub to examine how food affects us psychologically, from improving our moods to helping to treat severe mental illnesses, was opened at the University of Edinburgh last September, funded by the Medical Research Council.
As Danny Smith, a professor of psychiatry at the university, and principal investigator at the hub, explains: ‘We think the Mediterranean diet [rich in fruit and veg, wholegrains, seafood, beans, nuts and olive oil] is a good idea, but we don’t have deep detail on this in research terms. We are going into unexplored territory.’
In fact, a pioneering researcher in Australia, who has done nearly 20 years of work in this area, believes the case is already extremely strong for the mental health benefits of the Mediterranean diets and similar natural food regimens.
Ally Houston says changing his diet has helped control his ADHD and depression
When Professor Felice Jacka began studying food’s effect on brain health as a PhD student in the early 2000s, she endured scepticism and disbelief.
‘Back then, psychiatry was only about what happens above the neck,’ she told Good Health. ‘No one was looking at how gut health affects mental health. Trialling healthy diet as a way of actually treating – rather than preventing – mental illness was really going where angels feared to tread. People thought we were naïve, if not bonkers.’
Now she is a professor of nutritional psychiatry and director of the Food and Mood Centre at Deakin University in Geelong, Australia, the world’s first research facility focusing on nutritional psychiatry.
Professor Jacka founded the centre in 2017, the year she published a pioneering study in the journal BMC Medicine, for which 33 people with major, drug-resistant depression were put on Mediterranean diets for three months and compared with 34 people with the same condition who continued on their usual diets. The Mediterranean diet group experienced ‘significantly greater improvement’ in symptoms than the control group.
And a large-scale study Professor Jacka co-authored last year showed Mediterranean diets may prevent depression as well as treat it.
Data from 3,000 adults showed that, after six years, those who followed Mediterranean diet principles had a 16 per cent lower risk of developing depression than people who didn’t.
These results were echoed in a review of previous studies, involving more than 1,500 adults, which showed that Mediterranean diets ‘appear to have substantial potential for alleviating depressive symptoms in people experiencing major or mild depression’, reported the journal Nutrition Reviews.
Professor Jacka says she is convinced that a significant depression-lowering component of the Mediterranean diet – and similar diets rich in whole foods – is the high levels of fibre from fruits, vegetables, beans, pulses and grains.
Fibre, she says, richly supports a healthy gut microbiome – the population of bacteria, viruses and fungi that live in our digestive tract. ‘Where mental health is concerned, our gut microbes are running us,’ says Professor Jacka.
Fibre’s mood benefits have been demonstrated in a review of 18 previous studies, published in the journal Nutritional Neuroscience in 2023. The researchers at the University of Adelaide found that, for people at risk of depression because of previous low mood symptoms, each additional 5g of fibre they added to their diet was associated with a 5 per cent reduction of their risk in developing symptoms.
The researchers speculated that fibre may encourage the growth of ‘friendly’ bacteria that produce precursors to chemicals in the body such as serotonin and tryptophan which can act as mood-lifting ‘feelgood’ brain hormones.
Dr Iain Campbell has altered what he eats to manage his bipolar disorder
Nutritional psychiatry is not only about beneficial foods, it also studies the dark side of our diets, specifically the damaging effects on mental health that appear to result from diets high in ultra-processed foods (UPFs). A simple definition of UPFs is packaged foods made using industrial processes with ingredients you would not find in your kitchen.
Professor Jacka co-authored a study in the journal Clinical Nutrition which studied data from more than 16,000 adults and concluded that a person’s risk of depressive symptoms goes up by 10 per cent for each additional 10 per cent of their diet that comprises UPFs.
‘If you do just one thing to improve your mental health through diet, completely cut out soft drinks, ice cream and crisps,’ Professor Jacka told Good Health.
While the exact cause is not clear, one theory is that a poor diet, such as one high in UPFs, is linked to chronic inflammation, which in turn is linked to poorer mental health.
Meanwhile, researchers are focusing on one particularly stringent diet regimen as a candidate for alleviating serious mental illnesses such as bipolar disorder, schizophrenia and major depression.
This regimen, the ‘keto’ diet (short for ketogenic), involves drastically reducing intake of energy-giving carbs such as bread and rice. These are replaced by large amounts of fats such as olive oil and butter. Instead of being able to use carbs for energy, the liver breaks down these fats into compounds called ketones, which can then be used for fuel, a process called ketosis.
Since the 1920s, keto diets have been used in mainstream medicine to help treat a major neurological condition – epilepsy.
A 2020 research review by the highly respected Cochrane organisation, found that ketogenic diets completely stopped seizures in up to 55 per cent of children with drug-resistant epilepsy and reduced the frequency of seizures in a significant proportion of others.
In adults with drug-resistant epilepsy, the report said it was unclear if ketogenic diets reduced seizure frequency or prevented them altogether due to the limited number of studies. It is still not fully understood why keto can be effective in this way, though it is thought that changing how the brain gets its energy can effectively stabilise it.
Now, Professor Smith and colleagues at the Edinburgh Hub for Metabolic Psychiatry plan to investigate keto diets.
He told Good Health: ‘The general idea is that using ketones as energy is a more efficient way for the brain to function. It may be closer to a more ancient evolutionary path, from times when humans consumed far fewer carbs.’
This science is still in its ‘early days’ he says. ‘On diet, the evidence is currently weak, especially in terms of treating severe mental illness. We’ve already done preliminary work with keto diet and bipolar disorder, which established that around nine out of ten patients can stick to the diet – now we’re looking to design studies that evaluate diet through randomised clinical trials [the gold standard for research, where a therapy is compared against a placebo or no treatment].’
He adds: ‘We plan to use diets as one part of lifestyle change that can help people to stay mentally well, along with healthy rhythms of sleep, exercise, social interaction and managing stress.’
Professor Smith’s keto investigations are supported by £400,000 funding from the Baszucki Group, a US philanthropic organisation established by the billionaire chief of the videogame giant Roblox, David Baszucki, and his wife Jan.
As Good Health has previously reported, the group has donated £1.6 million for research to investigate the keto diet for bipolar, schizophrenia and depression. This follows the experience of their son, Matt, 27, who has bipolar disorder.
Going on the diet freed him from severe illness, while also reducing his medication. (No one with severe mental illness should swap their medication for a diet without prior medical approval and supervision.)
Since the 1920s, keto diets have been used in mainstream medicine to help treat a major neurological condition epilepsy
Professor Smith emphasises that the case for keto is far from proven and says: ‘There have been lots of false dawns in psychiatry and we have to be rigorous and cautious with our research.’ Indeed, Professor Jacka is cautious about claims for a keto diet.
‘Scientific evidence is just not there to support it at the moment,’ she says. ‘It is good that people are studying this, but there is the problem that keto regimens can often be the opposite of what’s best for the brain, as they tend to be very low in fibre and thus starve our gut microbiome.’
At the University of Oxford, Ally Houston is about to lead a research study to see if keto can help to treat ADHD and depression. He told Good Health he was inspired by his own experiences.
‘Back in 2016 as a physics student, I was really struggling mentally – I felt debilitatingly anxious, depressed and distracted. I got diagnosed as having ADHD. I tried the conventional approach, taking Ritalin [a drug that is meant to increase focus and reduce impulsivity], but with no success.’
His scientific supervisor told him that he’d suffered from mental problems with chronic fatigue syndrome but going on a ketogenic diet had transformed him.
Ally Houston tried it. ‘Within weeks my ADHD symptoms quietened to almost zero,’ he says.
One working theory in nutritional psychiatry is that problems such as ADHD, depression and bipolar may often be caused by problems with the mitochondria – the ‘batteries’ of our cells that provide them with energy. It may be that by fuelling brain cells via fats rather than carbs, these mitochondria may work properly again.
While he says he’s had no problem sticking with a keto regimen, a review of previous studies, published in the journal Nutrition last year, found that others can struggle with trying to keep tempting carbs off their plate.
Aside from drop-out rates, keto diets potentially have their own particular risks for health, a report in the journal Frontiers In Nutrition warned in 2021.
It said study evidence on keto diets shows that cutting high-carb foods such as fruit, veg and grains, ‘increases the risk of vitamin and mineral deficiencies’.
The paper, written by US advocacy group, the Physicians Committee for Responsible Medicine, further warned that high-fat diets heavy in processed meat and saturated fat ‘are associated with increased inflammation and risk of developing conditions such as diabetes, cardiovascular disease, some cancers, and Alzheimer’s’.
Nevertheless, like Ally Houston, Dr Iain Campbell is convinced that the diet regimen helped him manage his bipolar disorder, a condition that affects 1.3 million in the UK.
He told Good Health: ‘The depression I experience from this is much less like feeling sad and much more like being deprived of the oxygen of life. I experienced periods of sheer desperation: I couldn’t move, I couldn’t think or function. I piled on weight.’
Dr Campbell tried numerous diets to lose weight but without success. ‘Then I started a strict version of the Atkins diet [a form of keto],’ he says. ‘I lost weight easily. But what surprised me was that I also had periods of remission from my bipolar depression.’
He read of the keto diet’s use with epilepsy. ‘The treatment for bipolar is often also anticonvulsant epilepsy drugs, so I thought that if keto worked for epilepsy, it might also work for bipolar. By tracking my condition I could see a correlation between keto and my psychiatric symptoms.
‘Eight years ago I published my first paper on this in the British Journal of Psychology, but no one seemed interested,’ he says.
This changed when the Baszucki Group began to fund research on keto diets. Now Dr Campbell is working with Professor Smith.
Dr Campbell says: ‘Keto is the most effective treatment I have tried in my life. It is not a miracle cure, but it allows me to live a normal life, which I’d otherwise not been able to do.’
Dark chocolate lifts mood and slows brain decline
A feelgood food showing scientific potential for mental wellbeing is, perhaps surprisingly, chocolate.
In 2022, for example, a study in the Journal of Nutritional Biochemistry of 48 volunteers found those eating high-cocoa dark chocolate felt significantly fewer negative emotions such as anxiety, depression, stress, sadness and worry.
The researchers, from Seoul National University, South Korea, said the benefits came only from high-cocoa chocolate – 85 per cent and above.
A feelgood food showing scientific potential for mental wellbeing is, perhaps surprisingly, chocolate
Why might it have this effect? Those eating chocolate that was high in cocoa (85 per cent or more) experienced a significant rise in levels of a bacterium called Blautia obeum, thought to be linked to mood.
The scientists said previous studies have reported that patients with major depressive disorder have low levels of Blautia obeum in their gut.
And further good news about chocolate comes from a 2022 review of 19 previous studies into brain ageing and diet. It concluded that cocoa contains substances that appear to slow the rate of cognitive decline in older people.
However, the researchers, writing in the journal Antioxidants, added that, at present, ‘the molecular mechanisms of cocoa action on the central nervous system are not completely understood’.
