Dr Michael Mosley: how diet could conquer depression

In recent years we have seen a big rise in anxiety among teenagers, but that seems to be largely the result of rising exam pressure, not social pressure. My daughter told me recently that she had never experienced such a prolonged period of stress as in the run-up to her exams.

But teenagers aren’t the group who are most under the cosh. Surveys suggest that happiness and life satisfaction start to fall when you hit 35, and don’t really recover until you hit 60. It is people aged from 65 to 79 who report the highest levels of personal wellbeing and happiness. Little wonder then that one in five of us is now said to experience anxiety or depression, and there has been a dramatic increase in the use of drugs to combat this.

Last year British doctors wrote a record number of prescriptions for anti-depressants – around 70 million, double the levels they were prescribing ten years ago.

Is this too many? Sir Simon Wessely, professor of psychological medicine at the Institute of Psychiatry, tells me he thinks the real scandal is not that doctors are over-prescribing, but that so many people with depression are left untreated.

“We know from big studies that perhaps half the people who have depression are getting treatment. If that was the case in cancer, we would be absolutely appalled. The problem is that people still feel stigmatised, ashamed, reluctant to come and seek help.”

I can see the value of anti-depressants in the right circumstances, but I can’t imagine there are many, apart from the pharmaceutical companies, who want to see ever more prescribing.

So why aren’t we looking more seriously at other ways to prevent or treat mental health problems? I think there are important physical reasons for the rise in depression and anxiety, which often get overlooked when we go in search of psychological explanations.

Lack of sleep is one, but my personal obsession is the impact of food on mood. It seems obvious to me that what you eat and drink is going to affect your mental as well as your physical health, but there have been surprisingly few good-quality studies that have looked into this.

A recent exception was a study called “Smiles”, carried out in Australia. For this study they randomly allocated patients with moderate or severe depression – most of whom were on medication or having psychotherapy – either to get more social support or to go on a “Mediterranean” diet.

Those allocated to this diet were asked to cut back on sugary drinks and fast food, instead encouraged to eat more vegetables, nuts, unprocessed meat, fish and olive oil.

After 12 weeks there were striking differences between the two groups, with those on the Mediterranean diet achieving much lower scores for depression and anxiety. I realise that changing people’s eating habits is going to be a lot harder than prescribing pills, but for starters I would love to see medical students getting more nutritional training, so they are better prepared to offer advice when they become doctors.

I’m also keen to see what impact, if any, the new tax on sugary drinks has. It’s a modest first step, but an important one. With the average five-year-old in the UK consuming their own weight in sugar every year, we are storing up real problems for the future.

Trust Me, I’m a Doctor: Mental Health Special is on Wednesday at 9pm on BBC2