Vitamins and minerals found in fresh vegetables may help to keep Britain's overcrowded jails out of crisis, it was claimed today.

A study by researchers at the Aylesbury young offenders' institution in Buckinghamshire found that adding the nutrients to the inmates' diet "remarkably" reduced anti-social behaviour in the unit.

In what is claimed to be one of the first projects in the world to demonstrate scientifically what causes offending it is hoped that its findings might help prevent crime and lead to a fall in the prison population.

Bernard Gesch, lead author of the study at Surrey university, said: "In the future we may have a choice where we continue to lock up even more of our children, or we nourish them properly.

"The study did take place in a prison regime, but since every one of us needs these nutrients regardless of being in prison, there is every reason to think it may also reduce offending in the community when poor diets are consumed."

Half of the 230 inmates in the Home Office-backed study were given a supplement containing vitamins, minerals and fatty acids while the rest received dummy pills.

Organisers recorded the number and type of offences each of the prisoners committed nine months before the trial began and then for nine months with the food supplement.

The inmates taking the extra nutrients committed a quarter fewer offences than the other group. The major implication being that boosting diet can be a cheap and effective way to prevent offending.

Researchers said the greatest reduction was for serious offences including violence, where there was a drop of nearly 40%, while there was no reduction among those on the dummy pills.

Although reasonable food was available in jail most inmates plumped for the least healthy option, they added.

An estimate by Natural Justice, the charity that commissioned the report, suggested it would cost £3.5m a year to give all prisoners the nutrient supplements at the cost of less than a £1 a day per inmate where healthy fresh food was not available.

It at present costs £80 a day to keep someone in a young offenders' institution, the report's authors said.

The pills contain nutrients crucial to the biochemical processes that produces brain neurotransmitters like serotonin and dopamine, which are known to affect mood.

Mr Gesch said the approach needs to be re-tested but appeared to be a cheap and humane method to combat re-offending.

"We tend to forget that humans are physical as well as psychological beings and putting poor fuel into the brain seems significantly to affect social behaviour.

"Since humans are as much physical as social, it should not come as a surprise then that behaviour is governed by a combination of volition, social and physical determinants.

Natural Justice said it planned to repeat the study on a much larger scale at three young offenders institutions with a team of independent scientists.

It then hopes to draw up a diet that could cut the risk of offending in prison and outside.

The charity's chairman, Bishop Hugh Montefiore, said the research showed that lack of proper nutrition was a previously unknown major contributor to anti-social behaviour.

"We all know that proper nutrition is necessary for physical health. There is now increasing interest in its importance for mental well-being," he said.

The former chief inspector of prisons, Sir David Ramsbotham, urged the Prison Service to examine the results carefully.

"If healthy eating is part of a healthy lifestyle, and a healthy lifestyle is a crime free lifestyle, I hope that they will look seriously at exploiting the evidence presented to them today," he said.

The young offenders who took part were all volunteers serving average sentences of four years. None of the inmates knew who was taking the supplements or who else was in their group.