Leptin resistance is a condition in which the body's cells do not respond properly to the hormone leptin. Leptin is produced by fat cells and plays a key role in regulating energy balance and body weight.

It works by sending signals to the brain to reduce food intake and increase energy expenditure when energy stores (such as fat) are sufficient. In individuals with leptin resistance, the brain does not receive these signals properly, leading to an imbalance in energy intake and expenditure and potentially resulting in weight gain.