Campaigners are claiming diets can play a key role in mental health problems.
One man speaks about how he feels cutting out certain foods made a world of difference to his life.
Brian Godfrey suffered from depression for 40 years
Brian Godfrey suffered from chronic depression for about 40 years.
He first started having trouble when he was a teenager and over the years tried everything from drugs to psychotherapy.
By the 1960s the situation had got so bad that he was thinking about suicide.
"It was terrible, I would wake up in the morning with a fuzzy head and just could not get going. I felt tired and depressed.
"Some days it would be so bad I would lay in bed crying."
Mr Godfrey said it was only when it became clear the advice doctors were giving him was not going to work that he decided to look for something else.
"I went to the library and found a book about food intolerance."
The 71-year-old then cut out wheat and dairy and within three weeks was feeling better.
"It was a miracle. I just woke up one morning and my problems had gone."
In time, Mr Godfrey, from London, also stopped eating grains, eggs, chocolate, coffee, tea and his favourite drink, Guinness.
"I used to love to have a drink of Guinness after a meal, but that had to go. It was hard.
"I am very careful what I eat now, especially when I go out for a meal. My main diet is meat, fish, vegetables and fruit and I only eat organic food."
And Mr Godfrey, who is now completely free of the severe depression which plagued him during the first half of his life, said other people should consider altering their diets if they are having problems.
"It is becoming clear food is linked to mental illness. I would say that the things you most like are what most cause you harm. It is worth trying to cut them out."