Why can you not stop eating until you scarf down a whole bag of Doritos?  Is it a special gene? Epigenetics, like your mom ate one when she was pregnant with you, or is Frito-Lay just fiendishly clever?

Ban-happy critics blame fat and carbohydrate content but a new study found that was not the case. If it were, we could just add ingredients to unpopular foods like Brussels sprouts and affect the rewards center in the brain positively so people eat more of those. 

At the ACS meeting in New Orleans, Tobias Hoch, Ph.D., tackled the causes of a condition (because everything is a condition with a label these days) called "hedonic hyperphagia" that plagues hundreds of millions of people around the world. Namely, they like to eat. So they don't just eat due to hunger, they eat for pleasure. 

The team at FAU Erlangen-Nuremberg, in Erlangen, Germany, probed the condition by allowing one group of laboratory rats to feast on potato chips. Another group got bland old rat chow. Scientists then used high-tech magnetic resonance imaging (MRI) devices to peer into the rats' brains, seeking differences in activity between the rats-on-chips and the rats-on-chow. In the study, even when rats were fed the same mixture of fat and carbohydrates found in the chips, the animals' brains reacted much more positively to the chips, even on a full stomach.  

"The effect of potato chips on brain activity, as well as feeding behavior, can only partially be explained by its fat and carbohydrate content," explained Hoch. "There must be something else in the chips that make them so desirable." 

In the study, rats were offered one out of three test foods in addition to their standard chow pellets: powdered standard animal chow, a mixture of fat and carbs, or potato chips. They ate similar amounts of the chow as well as the chips and the mixture, but the rats more actively pursued the potato chips, which can be explained only partly by the high energy content of this snack, he said. And, in fact, they were most active in general after eating the snack food.

Although carbohydrates and fats also were a source of high energy, the rats pursued the chips most actively and the standard chow least actively. This was further evidence that some ingredient in the chips was sparking more interest in the rats than the carbs and fats mixture, Hoch said.

Hoch explained that the team mapped the rats' brains using Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) to monitor brain activity. They found that the reward and addiction centers in the brain recorded the most activity. But the food intake, sleep, activity and motion areas also were stimulated significantly differently by eating the potato chips.

"By contrast, significant differences in the brain activity comparing the standard chow and the fat carbohydrate group only appeared to a minor degree and matched only partly with the significant differences in the brain activities of the standard chow and potato chips group," he added.

Since chips and other foods affect the reward center in the brain, an explanation of why some people do not like snacks is that "possibly, the extent to which the brain reward system is activated in different individuals can vary depending on individual taste preferences," according to Hoch. "In some cases maybe the reward signal from the food is not strong enough to overrule the individual taste." And some people may simply have more willpower than others in choosing not to eat large quantities of snacks, he suggested.

If scientists can pinpoint the molecular triggers in snacks that stimulate the reward center in the brain, it may be possible to develop drugs or nutrients to add to foods that will help block this attraction to snacks and sweets, he said. The next project for the team, he added, is to identify these triggers. He added that MRI studies with humans are on the research agenda for the group.