Junk food may be as addictive as heroin and tobacco, a study has shown.
Obesity researchers found fatty and sugary snacks trigger the same 'pleasure centres' in the brain that drive people into drug addiction - making them binge on unhealthy food.
The findings could partly explain the soaring obesity rates in Britain and the success of fast food outlets.
Experts studied rats fed on cheesecake, bacon and sausages. Soon after the experiments began the animals began to bulk up and show signs of addiction.
'It presents the most thorough and compelling evidence that drug addiction and obesity are based on the same underlying neurobiological mechanisms,' Professor Paul Kenny said.
In the study, the animals completely lost control over their eating behaviour and continued to over-eat even when they anticipated receiving electric shocks, highlighting just how motivated they were to consume the palatable food.'
During the trial the animals were rewarded with a pleasurable electrical stimulation.
The rats could control how much of the stimulation they got by running on a wheel. Animals living on junk food ran far more - suggesting they needed more brain stimulation to feel good, the researchers found.
The scientists at the Scripps Research Institute in Jupiter, Florida, also gave rats electric shocks on their feet when they ate high-fat food.
Rats on a normal diet quickly learned to avoid the unhealthy food. But those used to junk food refused to let the shock get in their way of their high calorie food.
'They always went for the worst types of food,' said Professor Kenny, who published his findings in the journal Nature Neuroscience.
'When we removed the junk food and tried to put them on a nutritious diet they simply refused to eat.'
The researchers found junk food altered the chemical balance in the brain's 'reward circuits' - the parts of the brain that handle the feel-good chemical dopamine.
Identical changes happen in the brains of rats given cocaine or heroin and are thought to play a key role in drug addiction.
Britons are the world's biggest junk food addicts. At the same time, the average adult eats just over three portions of fruit and vegetables a day - the recommended number is five.
We will also get through 22,000 ready meals, sandwiches and sweet snacks in a lifetime - just under one a day.