Some of Britain's most challenging young prisoners are to be given food supplements in a study aimed at curbing violent behaviour.
Scientists from Oxford University say the effect of nutrition on behaviour has been underestimated. They say increases in consumption of "junk" food over the past 50 years have contributed to a rise in violence.
The university will lead the £1.4m study in which 1,000 males aged 16 to 21 from three young offenders' institutions in England and Scotland will be randomly allocated either the vitamin-and-mineral supplements or a placebo, and followed over 12 months.
In a pilot study of 231 prisoners by the same researchers, published in 2002, violent incidents while in custody were cut by a more than a third among those given the supplements. Overall, offences recorded by the prison authorities fell by a quarter.
John Stein, professor of physiology at Oxford University, said: "If you could extrapolate from those results you would see a reduction of a quarter to a third in violent offences in prison. You could reduce violent offences in the community by a third. That would have a huge economic benefit."
"Our initial findings indicated that improving what people eat could lead them to behave more sociably as well as improving their health. This is not an area currently considered in standards of dietary adequacy. We are not saying nutrition is the only influence on behaviour but we seem to have seriously underestimated its importance."
Mark Walport, head of the Wellcome Trust, which is funding the three-year study, said: "If this study shows that nutritional supplementation affects behaviour it could have profound significance for nutritional guidelines, not only within the criminal justice system but in the wider community – in schools, for example. We are all used to nutritional guidelines for our physical health but this study could lead to revisions taking account of our mental health."
The theory behind the trial is that when the brain is starved of essential nutrients, especially omega-3 fatty acids, which are a central building block of brain neurons, it loses "flexibility". This shortens attention spans and undermines self-control. Even though prison food is nutritious, prisoners tend to make unhealthy choices and need supplements, the researchers say.
Bernard Gesch, a senior research scientist in the department of physiology and the director of Natural Justice, a charity that investigates the causes of offending, said the prisoners would be given the supplement containing 100 per cent of the recommended daily amount of more than 30 vitamins and minerals plus three fish-oil capsules totalling 2.25g on top of their normal diet.
"We are trying to rehabilitate the brain to criminal justice. The law assumes crime is a matter of free will. But you can't exercise free will without involving your brain and the brain can't function properly without an adequate nutrient supply. It may have an important influence on behaviour."
"This is a positive approach to preventing the problems of antisocial and criminal behaviour. It is simple, it seems to be highly effective and the only "risk" from a better diet is better health. It is a rare win-win situation in criminal justice."
The Ministry of Justice is backing the three-year study, which will start in May. David Hanson, the Prisons minister, said he hoped it would shed further light on the links between nutrition and behaviour.
The Food Standards Agency says there is not enough evidence to show harm from additives or benefit from fish-oil supplements.
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