Jason has a similar reaction to bread. He has always loved doorsteps smothered in butter for breakfast. But it gives him diarrhoea and a weird kind of depressed 'hangover'. This makes him crave the heroin that once put his life on the skids.

It may sound implausible, but a controversial theory is gathering momentum: that one explanation for crime may be found on our dinner plates. The premise is that the brain needs the right fuel to function properly - otherwise it will misbehave.

This week, the first clinic in Britain to tackle juvenile delinquency by studying what children eat, then treating them with nutritional medicine and psychotherapy, will open its doors. Its consultant will be Peter Bennett, a former officer with West Yorkshire police.

The Cactus Clinic, at Teesside University in Middlesbrough, sprang from the work of the late Professor Steve Baldwin, who died in the Selby rail disaster, and Janice Hill, who runs the Overload Network, an Edinburgh-based charity for children with behavioural disorders.

Disturbed by a lack of alternatives to the throw-away-the-key approach to delinquency and the over-prescription of psychiatric drugs for children, they forged ahead with their maverick idea. The nutritional approach was based on a wealth of global research into the effects of vitamins, minerals and other compounds such as amino acids on brain chemistry.

Last year a study in the British Journal of Psychiatry suggested that reoffending by juvenile delinquents could be slashed by a quarter if they improved their diets. Some 230 inmates at the young offenders' institution in Aylesbury, Bucks, were assessed over 18 months by researchers from Oxford University. Half were given pills containing vitamins, minerals and essential fatty acids, and the other half placebo capsules in a double-blind, randomised trial.

The first group committed 25 per cent fewer offences than the second. The greatest reduction was for serious offences, including violence, where there was a fall of nearly 40 per cent. There was no decline in reoffending for those taking dummy compounds.

But despite evidence that alternative treatments may work, society, mainstream medicine and the prison authorities remain unimpressed. 'It's a crazy notion that we can accept that 10 pints of beer - which, after all, is derived from wheat - can affect behaviour, but not other foodstuffs,' said Hill.

She said nutritional intervention was not a quick fix that promised a speedy improvement in mood, like the new generation of anti-depressants. It took weeks to build up a malnourished brain and programmes had to be tailor-made.

In many cases, it is difficult to pinpoint the offending food type. John, who became more aggressive after eating tomatoes, lacked an enzyme that detoxifies a compound found in tomatoes, consisting of salicylates. It is believed these caused a chemical reaction in his brain, which then affected his behaviour.

'The children we see have psychological problems linked to physical problems, often caused by nutritional deficiencies. Children should have access to basic tests that can quickly establish nutritional status rather than having their knuckles perpetually rapped,' said Hill.

Hill came across Peter Bennett when she saw a QED documentary about his work with young criminals in Yorkshire. They were assessed for nutritional shortfalls and food allergies and put on individual programmes to address their problems. Bennett was astonished by the changes he witnessed.

He stumbled upon the work of a number of nutritionists during a study sabbatical at Oxford University. Disappointed that the force did not take his findings more seriously, he quit his job and trained as a nutritionist. He continues to get remarkable results from his patients. 'One child has just been accepted back into mainstream school, which is significant because, once you are excluded, you are usually excluded for good,' he said.

Other possible explanations for violent outbursts that Bennett has investigated include blood sugar imbalances, often attributed to over-reliance on refined sugar. He has studied the effect of fluctuating blood sugar on women who have used the defence of PMT in murder trials. He says that, a few days before menstruation, the release of female hormones can wreak havoc with blood sugar.

'If women then eat something like a bar of chocolate or drink an alcoholic drink, it will boost them up very rapidly, but then they go crash because the blood sugar rush is quickly used up. This can provoke rage and violent outbursts.'

The problem is not confined to pre-menstrual women - teenagers of both sexes weaned on junk food diets whose hormones are just kicking in are prime candidates for hypoglycaemia (low blood sugar). Swapping simple sugars for more complex carbohydrates, such as bread, rice and pasta that don't spark the same glucose rush, offers a solution.

Hill, whose charity offers support to children with ADHD (attention deficit hyperactivity disorder) insists that many of their restless, agitated symptoms can be traced back to the foods they have eaten, and not just sugars and additives.

Her own daughter, Debbie, now 17, has suffered from ADHD since childhood and was both disruptive and aggressive. Hill swiftly identified the foods that knocked her off balance, which included apples and strawberries, and introduced a raft of supplements including high doses of vitamin C, B6 and zinc and essential fatty acids into her diet. She calmed down significantly.

Eat your way out of trouble

Zinc, found mainly in shellfish and green leafy vegetables, has a calming effect on the central nervous system. Deficiencies are common after the consumption of food and drinks containing tartrazine, a colouring known to disturb behaviour in some youngsters.

Essential fatty acids (EFAs) are well-known mood regulators and are especially calming for women with PMT. Their ability to balance hormones makes them particularly useful for teenagers.

B6 (pyridoxine) is important for normal brain function and is found in broccoli, lentils, bananas and nuts. Deficiency symptoms include hyper- irritability, depression, fatigue and learning difficulties.

Calcium and magnesium are natural tranquillisers. They help to relieve anxiety and nervousness, tantrums and depression and have been used to combat aggression. They are found in dairy foods, fish and green leafy vegetables.

B5 (pantothenic acid) is known as the anti-stress vitamin and is involved in the production of neurotransmitters in the brain that regulate mood. It is found in eggs, kidneys, mushrooms and pork.