The medical profession has taken a long time to accept that what we eat has a big impact not just on our bodies but also on our brains. In fact, one of the earliest studies looking at the impact of food on depression was carried out by Prof Felice Jacka, from the Food and Mood Centre in Melbourne, and she told me it was a real struggle to get patients and to get funding.


For Jacka’s study, 67 patients with moderate or severe depression were randomly allocated to either a Mediterranean-style diet or ‘social support’. Those allocated to the Mediterranean-style diet were asked to eat more vegetables, fruits, nuts, eggs, fish and olive oil. They cut back on sweets, refined cereals, fried food, fast food, processed meats and sugary drinks.

Despite the relatively small number of people in the trial, after 12 weeks they saw significant differences between the two groups, with 32 per cent of those on the Med diet going into remission (able to reduce medication and no longer considered ‘moderately depressed’) compared with 8 per cent in the control group.

Those who stuck closest to the Mediterranean diet enjoyed the biggest improvement in mood. Since then, several other groups have made similar findings.

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So what’s going on? Well, some of the components of the Med diet (such as oily fish and the olive oil) have a well-established anti-inflammatory effect, and there is mounting evidence that many cases of depression and anxiety may be linked to brain inflammation. But the foods that make up the Mediterranean diet also boost ‘good’ bacteria in your gut, and they, in turn, produce their own anti-inflammatory compounds. Foods which have a positive effect on our mood are called ‘psychobiotics’.

As part of a new podcast series I’ve made for the BBC called Just One Thing, I interviewed Dr Kirsten Berding Harold, a researcher from University College Cork, who is part of a team who first coined the word, ‘psychobiotics’.

In one of her most recent studies she asked a group of volunteers to eat what she calls, ‘microbiota-friendly food’, which included more wholegrains, fruits and vegetables, but also fermented foods like kefir (a form of fermented yoghurt), which are rich in probiotics.

Their mood and microbiota were tested at the beginning and end of the study, and there were some impressive changes. Not only did their microbiome change, but as Kirsten explained, “after four weeks on the diet they felt a lot less stressed and had an improved mood. So the preliminary results suggest that it really does help your mood and mental health to eat a diet that is microbiota friendly.”

Further support for this theory comes from another recent study by researchers from the University of Surrey. They asked 64 young women to consume either a daily placebo or a capsule containing a prebiotic, a fibre that encourages the growth of ‘good bacteria’, for a month. At the end of the trial it was those who got the prebiotic capsules who reported the biggest improvements in anxiety levels and who also had better gut health.

More good reasons to improve your diet!



Dr Michael Mosley is former medical doctor, health writer and BBC presenter. He’s best known as presenter of Trust Me I’m a Doctor on BBC Two but has also written a number of bestsellers about personal health and medicine, including The Fast Diet, Fast Asleep and Fast Exercise.