Scientists in the US have claimed that fastfood such as hamburgers and fries could be physically addictive.

Dr John Hoebel and colleagues at Princeton University have found evidence to suggest that people can become over-dependent on the sugar and fat contained within fastfood.

The researchers found that rats fed a diet containing 25% sugar showed signs of stress when the sugar was removed. The rats suffered chattering teeth and shaking, similar to symptoms of nicotine or morphine withdrawal.

Hoebel said he believed that high-fat foods stimulate “pleasure chemicals”, or opoids, in the brain.

“The implication is that some animals – and by extension some people – can become overly dependent on sweet food,” he was quoted as saying by BBC Online.

Dr Jeane Randolph from the University of Toronto dismissed the theory, however, saying fastfood causes blood sugar to peak and then plunge, creating a natural desire for another snack.