Research aiming to discover the reasons for overeating has increased rapidly in recent years as the incidence of obesity in the United States has picked up pace. In 1980, the average US obesity rate was 15 percent; now the average is 34.3 percent, and another 32.7 percent are overweight. In particular, the personal and public cost of obesity-related diseases, such as type-2 diabetes and cardiovascular disease, has propelled research in the area.
This latest study, to be published in Biological Psychiatry, looked at the influence of ghrelin, a hormone that the body releases when it is hungry, in an effort to determine “why someone who is stuffed from lunch still eats – and wants to eat – that high-calorie dessert.”
Dr. Jeffrey Zigman, assistant professor of internal medicine and psychiatry at UT Southwestern and co-senior author of the study, said: “What we show is that there may be situations where we are driven to seek out and eat very rewarding foods, even if we’re full, for no other reason than our brain tells us to.”
Method
The researchers carried out two behavioral tests with mice: The first was intended to ascertain whether fully sated mice showed preference for a room in which they had previously found high fat food over one in which they had found regular chow.
When the mice were administered ghrelin, they preferred the room in which they had found high fat food, even though the room was now empty, while mice that had not been given ghrelin showed no preference, they found.
Lead author of the study and postdoctoral researcher in internal medicine Dr. Mario Perello said: “We think the ghrelin prompted the mice to pursue the high-fat chow because they remembered how much they enjoyed it. It didn’t matter that the room was now empty; they still associated it with something pleasurable.”
The second test recorded how many times mice continued to poke their noses into a hole in order to receive a pellet of high fat food. They found that those that had been administered ghrelin persisted for longer than those that had not.
Implications
“The findings of a role for ghrelin in food reward will likely have important implications in our overall understanding of energy balance regulation in both lean and obese individuals,” the authors wrote.
They added that their results suggested that it could be possible to develop drugs to target the effect of ghrelin as a reason for overeating without affecting other eating behaviors.
The researchers acknowledged that further studies were needed to establish the way in which ghrelin works in the brain to increase the rewarding value of high fat foods.
Source: Biological Psychiatry
2009, published online ahead of print
“Ghrelin Increases the Rewarding Value of High-Fat Diet in an Orexin-Dependent Manner”
Authors: Mario Perello, Ichiro Sakata, Shari Birnbaum, Jen-Chieh Chuang, Sherri Osborne-Lawrence, Sherry A. Rovinsky, Jakub Woloszyn, Masashi Yanagisawa, Michael Lutter, and Jeffrey M. Zigman.