Oily fish is increasingly missing from the diets of young people - and a leading nutritionist says this could harm their mental health.

The rates of mental illness and depression are increasing globally.

There is evidence that a chemical, Omega-3, found particularly in oily fish such as mackerel, herring, salmon and sardines has some effect on brain development.

And some believe that removing it from the diet could be partly contributing to the rise in mental problems.

Professor Michael Crawford, director of the Institute of Brain Chemistry and Human Nutrition at North London University, said: "We need to get back to feeding our minds as well as our bodies, otherwise the future of the nation is grim.

"We should all be eating oily fish at least once a week."

An NOP poll showed a particular decrease in fish consumption among the young.

Fish free

Three-quarters of 15 to 24-year-olds in the UK eat oily fish less than once a week.

Looking at all ages, almost a quarter never eat oily fish.

The average amount of fish eaten per person per week in the UK is thought to have halved over the past five decades.

Professor Crawford said: "A diet of fish containing Omega-3 was essential for the necessary cerebral expansion which transformed our predecessors into homo sapiens.

"Brain capacity expanded rapidly in our prehistoric ancestors living in east Africa near large freshwater lakes.

"Medical experts have long known of the benefits of oily fish in the fight against heart disease, but it is just as vital as brain food."

The National Institute of Medical Health in the US is currently sponsoring a study to examine the effectiveness of Omega-3 in treating a mental illness called bipolar disorder.

In the UK, attempted suicide has shown a sharp increase over the last decade.

Vegans and vegetarians get their Omega-3 from other sources, such as nuts and certain oils.