Leptin is released by fat cells – not in response to any signal, it is just released. That means that the more fat you have, the more leptin there is in your blood. Leptin is the signal to tell the hypothalamus how much fat we are carrying; it’s like the petrol gauge in your car telling you how much further you can go, how much energy there is in the tank.
Read the next section to understand how leptin acts in under and over-eating conditions
