Are you hungry right now? It could be because your brain doesn't have enough leptin.
Leptin is a hormone produced by fat cells that 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. When you eat food, leptin is created, and your hypothalamus signals you've had enough to eat, causing you to feel full.
However, 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.
Therefore, leptin not only signals when we've had enough to eat, but may also regulate the desire and craving for food, regardless of our actual needs.