A typical image shown to volunteers
Scientists have discovered why some people just can't resist food.
They used scans to show the reward centres in some people's brains are particularly sensitive to food advertising and product packaging.
Greater stimulation of this area by food images is likely to encourage over-eating, and obesity.
The study, published in the Journal of Neuroscience, was carried out by the Medical Research Council's Cognition and Brain Sciences Unit.
The researchers showed people pictures of highly appetizing foods (eg chocolate cakes), bland foods (eg broccoli), and disgusting foods (eg rotten meat).
At the same time, they measured brain activity using a sophisticated fMRI scanner.
After testing, the study participants completed a questionnaire that assessed their general desire to pursue rewarding items or goals.
The results showed that the participant's scores on the reward sensitivity questionnaire predicted the extent to which the appetizing food images activated their brain's reward network.
Lead researcher Dr John Beaver said: "Previous studies in this area have assumed that brain activation patterns are similar in all healthy individuals.
"But the new findings demonstrate that, even in healthy individuals, some people's brain reward centres are more sensitive to appetizing food cues.
"This helps explain why some individuals are more vulnerable to developing certain disorders like binge-eating.
"This is particularly pertinent in understanding the rapidly increasing prevalence of obesity, as people are constantly bombarded with images of appetizing food items in order to promote food intake through television advertising, vending machines, or product packaging."
According to Dr Beaver the findings may also have broader implications for understanding vulnerability to multiple forms of addiction and compulsive behaviours.
He said: "Research demonstrates that an individual's reward sensitivity may also relate to their vulnerability to substance abuse, and the brain network we have identified is hyper-responsive to drug cues in addicts."
Dr Ian Campbell, an expert in obesity from Nottingham and medical director of the charity Weight Concern, said appetite control was notoriously difficult and most dieters regularly fail to control their food intake.
"This research this shows that it's not simply explained by a loss of will power or greed. It's much more complicated.
"An involuntary exaggerated neurophysiological response to pictures of desirable food presented through clever advertising makes it incredibly difficult for some affected individuals to resist.
"The message is clear. While individuals must retain a responsibility to do their best to control their intake of high fat high sugar foods this responsibility must be shared by the food manufacturers and advertisers.
"We need to move away from a position of simply blaming patients to one of greater understanding, and support."