To understand leptin resistance, you first have to understand the role the hormone leptin plays in your metabolism. When you’ve eaten a meal, the fat cells throughout your body release leptin, which travels to the hypothalamus which is the part of your brain that helps regulate appetite. While there, it switches off neuropeptide Y — a protein that tells your brain you’re hungry — and switches on appetite-suppressing signals. In other words, it gives your brain the message to stop being hungry and start burning calories.
You’d think, then, that low levels of leptin would be the cause of an unstoppable appetite, but that’s not necessarily the case. Some research indicates that many people who are overweight actually have very high levels of leptin. How could this be? Well, the more fat you have, the more leptin you produce. And when the body continually cranks out excess levels of leptin in response to overeating, the receptors for leptin in the hypothalamus can start to get worn out and no longer recognize it. People with leptin resistance have high circulating levels of leptin, but the receptors are “deaf” to it, so it can’t shut off appetite or stimulate your metabolism.
This vicious circle is similar to what happens when a person develops resistance to insulin, the hormone that allows your cells to use the glucose in your blood. (Insulin resistance can cause high blood glucose levels and eventually lead to diabetes.) In fact, the two conditions often go hand in hand, and research suggests that leptin resistance may be reversed in the same way that insulin resistance can be reversed — by exercising, eating right, and losing weight.