What hormonal signal is known to increase appetite?

Ghrelin is a hormone produced mainly in the stomach and is often referred to as the "hunger hormone." It plays a significant role in regulating appetite and energy balance. When the stomach is empty, ghrelin levels increase, signaling to the brain that it is time to eat. This hormone stimulates hunger and promotes food intake, making it a key player in appetite regulation.

In contrast, insulin and leptin generally work to reduce appetite; insulin is released from the pancreas in response to food intake and helps regulate glucose levels, while leptin is produced by adipose (fat) tissue and informs the brain about energy storage, usually reducing hunger when fat stores are adequate. Cortisol, a stress hormone, can also influence appetite, but its effects are more complex and can contribute to increased appetite under certain stress conditions rather than as a direct signal to eat. Thus, ghrelin stands out as the primary hormone that actively promotes the sensation of hunger.