Giving leptin to rodents boosts the production of a specific protein in their fat tissue that helps generate heat. This happens because the nervous system acts like a messenger, carrying leptin's signals from the brain to the body's tissues to control how they burn energy and convert thyroid hormones.

Giving leptin directly to the brain of mice or rats tells their fat cells to produce more of a specific enzyme that converts thyroid hormones. This shows that signals from the brain can directly control how fat tissue processes hormones.

In Chinese adults, the gene that makes the hunger-controlling hormone leptin is less active in fat stored around the organs inside the belly compared to fat stored under the skin, whether someone is lean or obese.