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    Brain Study Shows Fat Hormone Affects Desire for Certain Foods

    Aug. 9, 2007 -- A new British study shows that the fat hormone leptin may affect whether people desire, dismiss, and delight in certain foods.

    Leptin is a hormone that's mostly made by the body's fatty tissue. It plays a role in regulating weight and appetite.

    The new British study centers on two teens who have a rare genetic condition that blocks their body from making leptin. The researchers included I. Sadaf Farooqi, MD, PhD, and Paul Fletcher, MBBS, MRCPsych, PhD, of the University of Cambridge.

    First, the 14-year-old boy and 19-year-old girl got their brains scanned with functional magnetic resonance imaging (fMRI) after fasting and 30 minutes after eating a meal.

    During the brain scans, the teens saw a series of 150 pictures.

    The pictures included 100 pictures of foods, including cakes, ice cream, puddings "and other things that people generally report as being 'mouth-watering,'" as well as bland foods such as potatoes, plain noodles, and broccoli, Fletcher tells WebMD via email.

    The remaining 50 pictures showed trees, cars, boats, and other things that aren't foods.

    Yum or Yawn?

    The researchers displayed each picture for four seconds. When a food picture popped onto the screen, the teens rated how much they liked and wanted that food.

    Next, the teens got leptin to treat their leptin deficiency.

    One week later, the teens repeated the brain scans after fasting and after eating a meal. Once again, they rated their interest in the food images displayed during the brain scans.

    Before leptin treatment, the teens wanted the foods that they saw during the brain scans more than they did after leptin treatment.

    They also reported being less hungry after fasting and fuller after eating the meal following leptin treatment, compared to their hunger and fullness ratings before receiving leptin.

    The brain scans show that certain areas of the brain were particularly active when the teens saw pictures of foods before leptin treatment. Those brains were less active -- and more typical of people without leptin deficiency -- after leptin treatment.

    The type of food also made a difference. For instance, the brain scans showed a small area of brain activity when a picture of broccoli was displayed, and a bigger area of activity when a strawberry was shown.

    The scientists conclude that leptin affects brain areas involved in desiring and enjoying foods. In short, leptin may affect whether the brain says "Yes, please," or "No, thanks," to foods people see.

    The study appears in the journal Science's early online edition, called Science Express.

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