| Thursday, 30 January, 2003, 10:20 GMT
Fast food 'as addictive as heroin'
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Researchers in the United States have found evidence to suggest people can become overly dependent on the sugar and fat in fast food.
The controversial findings add weight to claims that over-eating is simply down to a lack of self-control.
It may also explain soaring rates of obesity in the western world.Dr John Hoebel and colleagues at Princeton University in New Jersey based their theory on a study of rats.
'Cold turkey'
They found that rats fed a diet containing 25% sugar are thrown into a state of anxiety when the sugar is removed.
Their symptoms included chattering teeth and the shakes - similar to those seen in people withdrawing from nicotine or morphine, according to researchers.
Dr Hoebel said he believed high-fat foods stimulate opioids or 'pleasure chemicals' in the brain.
"The implication is that some animals - and by extension some people - can become overly dependent on sweet food," he said.
Further studies published in New Scientist magazine back up this theory.
Ann Kelley, a neuroscientist at the University of Wisconsin Medical School, the behaviour of rats after the were given sweet, salty and fatty foods.
She found a link between the brain's pleasure chemicals and a craving for this type of food.
She stimulated the rats' brains with a synthetic version of the natural opioid enkephalin. This caused rats to eat up to six times their normal intake of fat.
In addition, Dr Kelley identified long-lasting changes in rats' brain chemistry - similar to those caused by extended use of morphine or heroin.
Dr Kelley said: "This says that mere exposure to pleasurable tasty foods is enough to change gene expression and that suggests that you could be addicted to food."
However, other experts expressed doubts over whether people can become addicted to food.
Michael Jacobson, executive director of the Center for Science in the Public Interest, a nutrition lobby group in Washington DC, said there was a lack of evidence.
"I think the burden is on advocates of the addiction argument to provide evidence of addiction," he said.
Dr Jeane Randolph, from the University of Toronto, dismissed the theory. She said fast food causes blood sugar to peak and then plunge, creating a natural desire for another snack.
"It's a set-up for a late-afternoon binge rather than addiction," she said.