Researchers in the US used functional magnetic resonance imaging (fMRI) to reveal that during food craving episodes, craving-specific activation was seen in three regions of the brain: the hippocampus, insula, and caudate. These same three areas have also been reported to be involved in drug craving.
"We need to know more about food cravings in pathological conditions such as obesity, alcoholism, cocaine addiction, and so on. If all these excesses of desire share common brain mechanisms, then it might be possible to use motivational trades-off to treat cravings for harmful substances by substituting craving for something healthier, such as good food," said the study author Marcia Levin Pelchat, at the Monell Chemical Senses Center.
Almost one third of people living in the European Union are overweight and more than one in ten is now obese, according to European Association for the Study of Obesity. And the numbers of children who are overweight is set to rise from 20 per cent to 25 per cent by 2008, according to Datamonitor.
Consumer groups have singled out the food industry as a key player in this obesity epidemic of today that affects some 300 million people worldwide, and a further 750 million overweight people.
"Identifying the brain regions involved can tell us a great deal about the normal and pathological neurochemistry of craving, and in turn, lead us to better pharmacological treatments for obesity," continued Pelchat.
For the study, published in the December 2004 issue of NeuroImage, ten healthy volunteers were not permitted to consume anything other than a vanilla nutritional supplement beverage for the one-and-a-half days before the imaging session.
The researchers used the monotonous diet to increase the probability of cravings during fMRI sessions. Previous findings had shown that consuming a monotonous diet leads to large increases in the number of food cravings.
Subjects received enough of the beverage to provide sufficient calories and nutrients. A control group was allowed to eat whatever they wanted, along with several servings of the vanilla supplement.
Each subject provided names of two foods that they 'really like'. To trigger cravings during the fMRI scan, names of the liked foods and the liquid diet were alternated on a screen.
Subjects were then instructed to think about the food listed on the screen, along with its taste, smell, and texture. The researchers decided to use words as cues - rather than pictures - so each subject could imagine their own most desirable version of the liked food.
After the session subjects reported whether they had experienced any food cravings. As expected, the monotonous diet increased the likelihood of food craving when imagining the liked foods. All monotonous diet participants reported food craving while imagining the liked foods, but not while visualising the monotonous food.
Food cravings are very common, say the researchers, with surveys estimating that almost 100 per cent of young women and nearly 70 per cent of young men report having experienced cravings during the past year. The high prevalence of craving behaviour increases its potential nutritional impact, as cravings have been linked to snacking behaviour and diet compliance, both related to obesity.
Pelchat notes the significance of activation of memory structures: "During a craving we have a sensory memory or template for the food that will satisfy the craving. The food we eat has to match that template for the craving to be satisfied. It's as if our brain is saying, 'It has to be chocolate ice cream, lemon pie just won't do'."
"Cravings are also like habits. We often reach for a craved food without thinking of it," she adds.
J. Daniel Ragland at the department of psychiatry, University of Pennsylvania school of medicine, and responsible for the imaging part of the study continued: "The pattern of fMRI results suggests that memory areas of the brain responsible for associating a food with a reward are more important to food craving than are the actual reward centers."