Eat it up and be a good boy

SUPPLEMENTS are all the rage: evening primrose oil; St John's wort; fish oils; glucosamine; selenium; zinc; iron; molybdenum; probiotics. And don't forget those old standbys, multivitamin tablets. It is hard to walk through a pharmacy without seeing a promise of clearer skin, a stronger immune system or less squeaky joints. But what about a pill or potion to make you better behaved?

That is exactly the intention of a study led by John Stein, a professor of neuroscience at Oxford University, that is about to start in three British prisons. Not only is there a growing body of evidence that good nutrition can improve behaviour, there is also a theoretical basis for supposing that a lack of essential nutrients has an impact on the way the brain works.

Dr Stein believes that the proper functioning of nerve-cell membranes and signalling molecules depends on adequate supplies of minerals, vitamins and fatty acids. To test the idea, his team will recruit 1,000 prisoners. Half of them will receive these supplements, while the others receive a placebo. Neither prisoners nor experimenters will know who got what until the trial is over.

The trial will replicate, on a larger scale, a study carried out by Natural Justice, a British charity, and published in the British Journal of Psychiatry in 2002. Then, 231 volunteers were given either capsules containing their official daily requirements of vitamins, minerals and essential fatty acids (such as omega-3s) or placebos. The trial lasted for nine months and during that time the number of offences committed by each prisoner was recorded. Those who received the extra nutrients committed an average of 26.3% fewer offences than those who got the placebo. For violent offences, the reduction was 37%.

Two years later a study in the Netherlands reached similar conclusions. Indeed, the number of disciplinary offences fell by almost half. Supplements were deemed so cost-effective that they would allow prison services to be improved at the same time as saving money.

Dr Stein's study will attempt to find out more details about how the supplements work. Blood samples will be taken and the levels of nutrients in these samples correlated with prisoners' “impulsivity” and the variability of their heart rates. Heart-rate variability, says Dr Stein, is a good index of the degree of control an individual has over his autonomic nervous system (which controls many of the internal organs). This in turn is a predictor of anti-social behaviour.

Although nobody is suggesting that diet is the only factor that determines whether someone will behave badly in prison, it is increasingly clear that a poor diet can make behaviour worse. Although nutritionists are often a little sniffy about dietary supplements, pointing out instead how important it is to eat the right food in the first place, there are corners of society in which people lack either the knowledge or the means to do so, or simply choose to eat poorly.

In British prisons, serving time in jail used to be known as “doing porridge”, because a bowl of oatmeal was an inmate's regulation breakfast. These days British prisoners have access to a far wider range of foods but nevertheless often make poor choices and consume diets that are far from ideal. So although prisoners, like anyone else, are well advised to choose a balanced diet, they may not pay much heed. Unless, of course, being forced to eat your greens becomes a standard part of a custodial sentence.