Hunger signaling involves both mechanical and chemical mechanisms.

“For instance, you have neurons, nerve cells in your gut that signal how stretched or nonstretched the walls of your stomach are, how full or how empty your gut is, and send that information to the brain to make you feel to some extent hungry or not hungry. In addition, there are chemical signals that go from the gut to the brain. For instance, we have neurons in our gut that can detect the presence of amino acids from proteins that we eat, fatty acids from the foods that we eat, the lipids, and sugars, different forms of carbohydrate.”