Feeling guilty for having seconds even though you're full? Your urge to keep eating can be due to hormones and evolution, says a new study led by Gene-Wang, MD, professor of psychiatry at Mount Sinai School of Medicine in New York. Findings also suggest that women may have more trouble saying no to food than men.

In order to understand why some people continue eating even when they are no longer hungry, researchers asked 13 women and 10 men to name their favorite foods and then presented those foods to the participants after they fasted for 20 hours. The participants were told that they were not allowed to eat the food but could smell and taste it.

Then they were asked to try to control their desire to eat the food while positron emission tomography (PET) scans examined their brain activity. While both genders were successful in controlling their urge to eat, the scans suggested that the women's brains reacted as if they were hungry.

Wang speculates that a woman's need to eat for two when she is pregnant and the increased quantity of food modern society now consumes may be the reasons behind the research results.