Which hormone is primarily responsible for stimulating hunger?

Ghrelin is known as the "hunger hormone" because it plays a crucial role in stimulating appetite and promoting food intake. It is produced primarily in the stomach and is released into the bloodstream, particularly during times of fasting. When the stomach is empty, ghrelin levels rise, signaling to the brain that it's time to eat. This hormone stimulates the hypothalamus, which is the area of the brain that regulates hunger and energy balance.

In contrast, insulin is primarily involved in glucose metabolism and helps regulate blood sugar levels after eating, while leptin is produced by adipose (fat) tissue and signals satiety or fullness to the brain, effectively reducing hunger. Cortisol, often referred to as the stress hormone, can influence appetite but is more associated with the body's response to stress rather than directly stimulating hunger. Thus, ghrelin is distinctly recognized for its role in initiating the feeling of hunger, making it the correct choice in this context.