Leptin

Leptin is a protein hormone synthesized and secreted primarily by adipocytes (fat cells) that acts as a long-term regulator of energy balance. It is often referred to as the 'satiety hormone' because its primary role is to inform the hypothalamus about the status of the body's fat stores. When fat mass increases, leptin levels rise, signaling the brain to suppress appetite and increase energy expenditure. Conversely, when fat mass decreases, leptin levels drop, signaling the brain to increase hunger and conserve energy.

In many cases of obesity, a condition known as leptin resistance occurs, where the hypothalamus becomes desensitized to the hormone's signal. Despite having high levels of circulating leptin due to abundant fat stores, the brain perceives a state of starvation, leading to persistent hunger and a lowered metabolic rate. Restoring leptin sensitivity is a critical component of hypothalamic resetting, as it allows the body to accurately sense its energy reserves and exit the defensive survival shift.