Why Do We Get Hungry ?

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Why do we get hungry? Why do we get hungry? And when we eat a meal, why at some point do we feel full? Until recently, we had no idea. Scientific research in the past 25 years has taught us that the stomach and small intestine send signals to the brain. Different signals turn our appetite up or down. Some of the signals are digestive hormones: chemicals that are made in the stomach and small intestine and travel through the blood to the brain. Other signals are hormones made by cells that store fat. Still other signals travel up nerves, particularly the vagus nerve, running from the stomach to the brain. When it’s been three to four hours since your last meal, your stomach makes a hormone called ghrelin (pronounced GRAY-lin) that travel in the blood to the brain. The brain responds by feeling hungry. When you’re eating a meal, your stomach and intestine make hormones that tell the brain to start feeling full. One hormone is called leptin, another is cholecystokinin (CCK). Stretch receptors in the stomach also are activated as the stomach fills with food or water. These receptors send signals up the vagus nerve to the brain, which tell the brain to feel full. It takes time for the various “full” signals to get their message through to our brain. In most of us, the signals don’t start getting their message through for 15 to 20 minutes after we start eating. And then it takes still more time before our brain says “Enough”. Let’s say you’re just sitting down for a meal. Your plate is full – 2,500 to 3,000 calories on it. Suppose, based on the amount of calories you’ve already burned that day, all you need from this meal to keep in energy balance is 1,500 calories. But you have no way of knowing that. All you know is that you are hungry, so you start to eat. If you eat slowly, your brain will start to feel full after about 15 minutes. A few

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