“Leptin is not our obesity hormone. Leptin is our starvation hormone,” says Robert H. Lustig, MD, professor of pediatrics at the University of California, San Francisco and a member of the Endocrine Society’s Obesity Task Force.
Leptin is a protein that’s made in the fat cells, circulates in the bloodstream, and goes to the brain. “Leptin is the way your fat cells tell your brain that your energy thermostat is set right,” Lustig says.
“Leptin tells your brain that you have enough energy stored in your fat cells to engage in normal, relatively expensive metabolic processes,” he says. “In other words, when leptin levels are at a certain threshold — for each person, it’s probably genetically set — when your leptin level is above that threshold, your brain senses that you have energy sufficiency, which means you can burn energy at a normal rate, eat food at a normal amount, engage in exercise at a normal rate, and you can engage in expensive processes, like puberty and pregnancy”.