Junk food really could be addictive and stimulate cravings in much the same way as an illicit drug, a brain scanning study has shown.
Scientists investigated how food intake is regulated by the brain's "pleasure centres" which are known to be linked to addiction.
Functional magnetic resonance imaging (fMRI) was used to observe the brain activity of overweight and obese volunteers for four hours after a meal.
This crucial period has been shown to influence behaviour the next time a meal is eaten.
Twelve men were given test meals designed as milk shakes that tasted the same and were matched for calories.
One milk shake contained rapidly digested high-glycaemic index (GI) carbohydrates, often found in junk food, while the other was made with low GI carbohydrates.
Consumption of the high GI drink was followed by an initial surge in blood sugar levels followed by a sharp crash four hours later.
The sudden decrease in blood sugar was associated with excessive hunger and intense activation of the nucleus accumbens, a brain region central to addictive behaviour.
Lead scientist Dr David Ludwig, director of the New Balance Foundation Obesity Prevention Centre in Boston, US, said: "Beyond reward and craving, this part of the brain is also linked to substance abuse and dependence, which raises the question as to whether certain foods might be addictive.
"These findings suggest that limiting high-glycaemic index carbohydrates like white bread and potatoes could help obese individuals reduce cravings and control the urge to over-eat."
The research is reported in the American Journal of Clinical Nutrition.