What is the primary function of the hormone leptin?

Leptin is primarily known for its role in suppressing hunger. It is a hormone produced by adipose (fat) tissue and plays a critical part in regulating energy balance within the body. When fat stores increase, leptin levels rise, signaling the brain to reduce appetite and increase energy expenditure. This process helps to maintain body weight by inhibiting feelings of hunger and promoting feelings of fullness or satiety after eating.

In contrast, circumstances that lead to decreased fat storage result in lower levels of leptin, thus prompting an increase in appetite. This feedback mechanism is essential for energy homeostasis and helps prevent excessive weight gain or loss. Other answer choices pertain to different physiological processes that leptin does not directly influence. For instance, while leptin does impact metabolism, its primary role is not to enhance glucose metabolism or regulate water retention, as these are managed by other hormones in the body, such as insulin and antidiuretic hormone (ADH).