Does television cause crime? The idea that people copy the violence they watch is debated endlessly by criminologists. But this column concerns an odder and perhaps more interesting idea: if crime leaps out of the box, it is not the programmes that are responsible as much as the material in between. It proposes that violence emerges from those blissful images of family life, purged of all darkness, that we see in the advertisements.

Let me begin, in constructing this strange argument, with a paper published in the latest edition of Archives of Pediatrics and Adolescent Medicine. It provides empirical support for the contention that children who watch more television eat more of the foods it advertises. "Each hour increase in television viewing," it found, "was associated with an additional 167 kilocalories per day." Most of these extra calories were contained in junk foods: fizzy drinks, crisps, biscuits, sweets, burgers and chicken nuggets. Watching television, the paper reported, "is also inversely associated with intake of fruit and vegetables".

There is no longer any serious debate about what a TV diet does to your body. A government survey published last month shows that the proportion of children in English secondary schools who are clinically obese has almost doubled in 10 years. Today, 27% of girls and 24% of boys between 11 and 15 years old suffer from this condition, which means they are far more likely to contract diabetes and to die before the age of 50. But the more interesting question is what this diet might do to your mind. There are now scores of studies suggesting that it hurts the brain as much as it hurts the heart and the pancreas. Among the many proposed associations is a link between bad food and violent or antisocial behaviour.

The most spectacular results were those reported in the Journal of Nutritional and Environmental Medicine in 1997. The researchers had conducted a double-blind, controlled experiment in a jail for chronic offenders aged between 13 and 17. Many of the boys there were deficient in certain nutrients. They consumed, on average, only 63% of the iron, 42% of the magnesium, 39% of the zinc, 39% of the vitamin B12 and 34% of the folate in the US government's recommended daily allowance. The researchers treated half the inmates with capsules containing the missing nutrients, and half with placebos. They also counselled all the prisoners in the trial about improving their diets. The number of violent incidents caused by inmates in the control group (those taking the placebos) fell by 56%, and in the experimental group by 80%. But among the inmates in the placebo group who refused to improve their diets, there was no reduction. The researchers also wired their subjects to an electroencephalograph to record brainwave patterns, and found a major decrease in abnormalities after 13 weeks on supplements.

A similar paper, published in 2002 in the British Journal of Psychiatry, found that among young adult prisoners given supplements of the vitamins, minerals and fatty acids in which they were deficient, disciplinary offences fell by 26% in the experimental group, and not at all in the control group. Researchers in Finland found that all 68 of the violent offenders they tested during another study suffered from reactive hypoglycaemia: an abnormal tolerance of glucose caused by an excessive consumption of sugar, carbohydrates and stimulants such as caffeine.

In March this year the lead author of the 2002 report, Bernard Gesch, told the Ecologist magazine that "having a bad diet is now a better predictor of future violence than past violent behaviour ... Likewise, a diagnosis of psychopathy, generally perceived as being a better predictor than a criminal past, is still miles behind what you can predict just from looking at what a person eats."

Why should a link between diet and behaviour be surprising? Quite aside from the physiological effects of eating too much sugar (apparent to anyone who has attended a children's party), the brain, whose function depends on precise biochemical processes, can't work properly with insufficient raw materials. The most important of these appear to be unsaturated fatty acids (especially the omega 3 types), zinc, magnesium, iron, folate and the B vitamins, which happen to be those in which the prisoners in the 1997 study were most deficient.

A report published at the end of last year by the pressure group Sustain explained what appear to be clear links between deteriorating diets and the growth of depression, behavioural problems, Alzheimer's and other forms of mental illness. Sixty per cent of the dry weight of the brain is fat, which is "unique in the body for being predominantly composed of highly unsaturated fatty acids". Zinc and magnesium affect both its metabolism of lipids and its production of neurotransmitters - the chemicals which permit the nerve cells to communicate with each other.

The more junk you eat, the less room you have for foods which contain the chemicals the brain needs. This is not to suggest that food advertisers are solely responsible for the decline in the nutrients we consume. As Graham Harvey's new book We Want Real Food shows, industrial farming, dependent on artificial fertilisers, has greatly reduced the mineral content of vegetables, while the quality of meat and milk has also declined. Nor do these findings suggest that a poor diet is the sole cause of crime and antisocial behaviour. But the studies I have read suggest that any government that claims to take crime seriously should start hitting the advertisers.

Instead, our government sits back while the television regulator, Ofcom, canoodles with the food industry. While drawing up its plans to control junk food adverts, Ofcom held 29 meetings with food producers and advertisers and just four with health and consumer groups. The results can be seen in the consultation document it published. It proposes to do nothing about adverts among programmes made for children over nine and nothing about the adverts the younger children watch most often. Which? reports that the most popular ITV programmes among two- to nine-year-olds are Dancing on Ice, Coronation Street and Emmerdale, but Ofcom plans to regulate only the programmes made specifically for the under-nines. It claims that tougher rules would cost the industry too much. To sustain the share values of the commercial broadcasters, Ofcom is prepared to sacrifice the physical and psychological wellbeing of our children.

At the European level, the collusion is even more obvious. Last week, Viviane Reding, the European media commissioner, spoke to a group of broadcasters about her plans to allow product placement in European TV programmes (this means that the advertisers would be allowed to promote their wares during, rather than just between, the programmes). She complained that her proposal had been attacked by the European parliament. "You have to fight if you want to keep it," she told the TV executives. "I would like to make it very clear that I need your support in this."

I spent much of last week trying to discover whether the Home Office is taking the research into the links between diet and crime seriously. In the past, it has insisted that further studies are needed, while failing to fund them. First my request was met with incredulity, then I was stonewalled. Tough on crime. To hell with the causes of crime.

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