The Facts on Leptin: FAQ
The truth about the hormone leptin and obesity.
It's been called the "obesity hormone" or "fat hormone" -- but also the
"starvation hormone." When scientists discovered leptin in 1994, excitement
arose about its potential as a blockbuster weight loss treatment. Even today,
the Internet is loaded with sites that sell leptin supplements. Any truth to
those pitches? And what exactly is leptin?
WebMD asked two experts on leptin to discuss how this hormone affects weight
and appetite, as well as other aspects of health.
Q. What is leptin?
"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".
But when people diet, they eat less and their fat cells lose some fat, which
then decreases the amount of leptin produced.
"Let's say you starve, let's say you have decreased energy intake, let's say
you lose weight," Lustig says. "Now your leptin level goes below your personal
leptin threshold. When it does that, your brain senses starvation. That can
occur at any leptin level, depending on what your leptin threshold is."
"Your brain senses that and says, ‘Hey, I don't have the energy
onboard that I used to. I am now in a starvation state,'" Lustig says.
Then several processes begin within the body to drive leptin levels back up.
One includes stimulation of the vagus nerve, which runs between the brain and
"The vagus nerve is your energy storage nerve," Lustig says. "Now the vagus
nerve is turned on, so you get hungrier. Every single thing the vagus nerve
does…[is] designed to make you take up extra energy and store it in your fat.
Why? To generate more leptin so that your leptin can re-establish its personal
leptin threshold... It causes you to eat and it causes you to get your leptin
back to where it belongs."
Q. How does leptin affect weight
"Here's the question: If this thing works like a thermostat -- an adipostat
-- why do we keep gaining weight?" Lustig says.