Answer: Ghrelin is made in the stomach. It stimulates hunger by entering the brain and acting on the neurons in the hypothalamus to increase the activity of the hunger-causing nerve cells and reducing the activity of hunger-inhibiting cells. As the stomach empties, the release of ghrelin increases. Our hunger is influenced not only by our physical state but also by our memory of when we last ate and our expectation of when we should eat again. And although we humans as a species prefer certain tastes (such as sweet and salty), we learn to satisfy those preferences with specific foods eaten in the context of our families and our culture. Some of our taste preferences, such as the avoidance of new foods or of foods that have made us ill, have survival value.
