Together, these physiological responses (along with other hormones and signals) help you feel full and know when to stop eating. Yet these still aren’t the complete picture, either. Your brain also drives your food consumption over time. What really matters to your weight and overall health, of course, is what you do consistently — i.e. what and how much you typically eat, day after day. Your body has a system for managing your long-term energy and nutrient needs. It’s called the leptin feedback loop.

Leptin is a hormone that’s released by fat tissue. Leptin tells the brain how much energy we’ve just consumed and how much excess energy we have stored up (as fat). The more body fat we have, the more leptin in our blood. The brain makes decisions based on leptin levels about hunger, calorie intake, nutrient absorption, and energy use and storage. Then, it cycles back to regulate leptin production in a loop that can help keep our energy (and body weight) balanced over time.