Eating a Mediterranean diet with plenty of fish, fruit, vegetables and nuts lowers a person’s risk of depression.
A review of dozens of studies found pescatarians who eat lots of plant-based foods are a third less likely to develop the mental-health condition.
Researchers today described the evidence to show there is a relationship between the quality of diet and mental health as ‘compelling’.
Mediterranean diets, also rich in olive oil, lentils and even red wine, are thought to lower inflammation, which may benefit a person’s mental health.
The University College London researchers analysed 41 studies that investigated the link between a person’s diet and their risk of depression.
Four of the studies specifically assessed the association between a traditional Mediterranean diet and depression in a total of 36,556 adults.
Results suggest those who most strictly follow a Mediterranean diet are 33 per cent less likely to suffer from depression than those who adhere to it the least.
‘There is compelling evidence to show that there is a relationship between the quality of your diet and your mental health,’ Dr Lassale said.
‘This relationship goes beyond the effect of diet on your body size or other aspects of health that can in turn affect your mood.’
The scientists also looked at five studies investigating the link between a poor diet and depression in 32,908 adults from France, Australia, Spain, the US and the UK.
Their study, published today in the journal Molecular Psychiatry, found eating lots of saturated fat, sugar and processed food increases a person’s depression risk.
Dr Lassale and colleagues now recommend people avoid inflammatory foods in favour of fruits, vegetables, lentils, chickpeas, fish, olive oil and nuts.
‘A pro-inflammatory diet can induce systemic inflammation, and this can directly increase the risk for depression,’ she said.
‘There is also emerging evidence that shows that the relationship between the gut and brain plays a key role in mental health and that this axis is modulated by gastrointestinal bacteria, which can be modified by our diet.’
The scientists also believe their findings support depression sufferers making changes to their diets, rather than immediately opting for antidepressants.
Co-author Dr Tasnime Akbaraly added: ‘Our study findings support routine dietary counselling as part of a doctor’s office visit, especially with mental health practitioners.
‘This is of importance at a patient’s level, but also at public health level, especially in a context where poor diet is now recognised to be the leading cause of early death across middle and high-income countries and at the same time mental disorders as the leading cause of disability.’
But Professor Naveed Sattar, from the University of Glasgow, argued people with depression may choose unhealthy foods, rather than their poor diet being the cause of their mental-health condition.
‘We really need large, well powered, intervention trials to test this to give this idea any credibility,’ he said.
‘Also the link to inflammation as a plausible mechanism to explain a link between diet and mind health is highly tenuous.
‘Thus, whilst eating healthier is good for many reasons, we need more evidence before we can say plant rich diets can improve mental health.’
The UCL scientists also stress further research is required to determine how dietary changes could affect a person’s mental health.
Around one in 10 people in the UK suffer from depression at some point in their lives. In the US, the condition affects around 6.7 million adults every year.
This comes after research released earlier this year suggested stopping exercise can worsen depression in as little as three days.
Six studies found patients’ symptoms reappear almost immediately after they stop being active, according to a review by the University of Adelaide.