Yaël: Mmmm! Peach pie!

Don: Oooh! Can I have some?

Y: Don! You ate a huge lunch, how could you be hungry?!

D: Maybe my brain doesn't have enough leptin?

Y: What's leptin?

D: It's a hormone produced by fat cells. Leptin plays a key role in regulating appetite      and metabolism. When you eat, fat cells release leptin, which then binds to receptors      in a part of your brain called the hypothalamus. So, lots of food, lots of leptin, and      your hypothalamus signals you've had enough to eat, and you feel full.

Y: Don, you just ate! Your brain should have PLENTY of leptin!

D: But scientists at Cambridge University discovered that leptin also influences the so-      called "reward centers" of the brain, which control food cravings and the pleasure we      feel from eating. Their study looked at brain activity and cravings in two rare patients      who can't produce leptin.

     Researchers scanned the brains of these volunteers in their leptin-deficient condition.      The subjects were shown photos of both food and non-food items after they had      been fasting, and again after eating.

     In the absence of leptin, the brain regions responsible for cravings were activated by      food images, and volunteers described the food images as highly desirable, whether      or not they were full.

     The subjects were then treated with leptin for seven days, and the experiment was      repeated. This time the reward centers were most active, and food images were      reported as more desirable when the subjects had been fasting.

     So not only does leptin signal when we've had enough to eat, but may also regulate      the desire and craving for food, regardless of our actual needs.

Y: Well, unfortunately for you and your cravings, I ate all the pie!  

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