Dr. Sadaf Farooqi and Dr. Paul Fletcher of the University of Cambridge, England, discovered that the appetizing properties of food have strong effects on the same key brain regions responsible for rewarding emotions and desires.

Using functional magnetic resonance imaging, the researchers found parts of the brain "light up" when people deficient in leptin are shown images of food.

Leptin is made by fat cells and circulates in the blood to reach the brain, where it acts to reduce hunger and increase fullness.

The researchers studied patients who had a rare genetic disorder resulting in a complete lack of leptin who excessively like all types of food and develop severe obesity.

After leptin treatment, the study participants said their hunger reduced and they became more picky about food -- and they lost weight -- the researchers reported in the journal Science.