Why We Continue to Eat When We're Full

Has this ever happened to you? You shovel the last bite of your delicious yet oversized meal into your mouth. As you loosen a notch on your belt buckle, wondering why you didn't wear stretchy pants, the waiter walks by and hands you the dessert menu. You know you are full. You know you should not get the triple-layer chocolate cake. But, you do. And, you eat the whole thing. Then you wonder why you just did that.

New research from the University of Texas Southwestern Medical Center suggests that ghrelin, the hormone that your body secretes when you are hungry, might also act on the brain influencing the hedonic aspects of eating behavior. The result is that we continue to eat "pleasurable" foods even when we are full.

Researchers Jeffrey Zigman, Mario Perello, and Michael Lutter suggest that ghrelin increases specific rewarding aspects of eating. Previous studies have linked ghrelin levels with the pleasurable feelings one gets from alcohol and cocaine.

Zigman explains that rewards give us sensory pleasure and motivate us to work to obtain them. Additionally, they facilitate the reorganization of our memory to remember how to obtain the rewards.

To study the effects of ghrelin on overeating, the researchers conducted two studies with mice. In the first study, the scientists observed whether mice that were satiated preferred a room where they previously found high-fat pellets versus a room that had regular bland food. When the mice were injected with ghrelin, they preferred the room with the fatty food. The mice without the ghrelin administration had no preference.

The researchers suggest that the mice with ghrelin pursue the fatty food because they remember how pleasurable it was. When researchers blocked the action of ghrelin, they found that the mice spent less time in the room that previously contained the high-fat pellets.

In the second study, the researchers measured how long the mice would continue to poke their heads into a hole to receive a pellet of high-fat food. They found that the mice that received ghrelin spent more time poking their heads in the hole, whereas the mice without ghrelin gave up sooner.The next time, you reach for the dessert menu, remember that just because your brain is telling you to get the triple-layer chocolate cake, ask yourself if it is really you wanting the cake or just ghrelin making you think that you do.