It is the phenomenon that explains why it can be so difficult to dip into a crisp packet without polishing off the entire contents. Likewise, a single bite of chocolate may prove waist-expandingly fatal. Some might call it greed, but another name for such behaviour is “hedonic hyperphagia”.
“That’s the scientific term for ‘eating to excess for pleasure rather than hunger’,” said Dr Tobias Hoch, who presented findings from a study on rats to the American Chemical Society in New Orleans.
“The chronic form is a key factor in the epidemic of overweight and obesity that in the United States threatens health problems for two out of every three people.” Dr Hoch and his team from the University of Erlangen- Nuremberg in Germany scanned the brains of rats as they ate crisps, a powdery mixture of fat and carbohydrates, or ordinary food pellets. The rats were far more keen on the crisps, despite the fat and carbs mixture containing the same number of calories. Standard pellets were the least popular food.
“The effect of potato chips [crisps] on brain activity, as well as feeding behaviour, can only partially be explained by its fat and carbohydrate content,” said Dr Hoch. “There must be something else in the chips that make them so desirable.” High levels of fat and carbohydrate had been thought to send pleasing messages to the brain, leading people to gorge on calorie-packed snacks. Magnetic resonance imaging scans showed that reward and addiction centres in the rats’ brains were most active when they ate crisps. Food intake, sleep and activity and motion areas were also stimulated differently by crisps compared with other food.
“Significant differences in the brain activity of the rats eating the standard food and the fat carbohydrate group only appeared to a minor degree. These differences matched only partly with the significant differences in the brain activities of the rats eating standard food and potato chips group,” Dr Hoch added.
Pinpointing the molecular triggers in snacks and sweets that stimulate the brain’s reward centres could lead to the development of new drugs or food additives that combat over-eating. Identifying the triggers is the German team’s next project.
Differing sensitivity to reward signals may explain why some individuals are more susceptible to moreishness than others, the scientists believe. “Possibly, the extent to which the brain reward system is activated in different individuals can vary depending on individual taste preferences,” said Dr Hoch.
“In some cases, maybe the reward signal from the food is not strong enough to overrule the individual taste.”