Your appetite is regulated by a hormone called leptin, which is produced by fat cells.
Leptin actually drives your behavior. It is a messenger. It communicates with the hypothalamus in the brain to control appetite. Normal levels of leptin send the message to stop eating. Conversely, if you are starving, with low levels of leptin in your body, you will prioritize finding food to eat, and will feel hungry. This mechanism would have helped our ancestors to survive when food was scarce.
When the hormone was first discovered in the 1990s scientists thought it might be a cure for obesity. People were injected with extra leptin, but they did not lose weight. Why not? It seems that when our bodies produce excess leptin, or are given extra, they become resistant to it. Scientists do not yet know how we become resistant to the hormone. However, when people become obese (and have high leptin levels), they may become resistant to the hormone’s messages to the brain. They feel as though they are starving, driven to eat more in the same way as a person who has low levels of leptin due to starvation.
Leptin is involved in more than appetite control. Low levels of leptin, affect the body’s fertility, and ability to enter puberty. There is research showing leptin is also important in the proper functioning of the immune system.
Remember, you might feel that you are choosing all your behaviors, but there is also the chemistry of your body, your hormones, which drive your actions. If you are obese, you may be leptin resistant, and this could be affecting your appetite so you feel hungry even when you already have enough fuel on board.