The Facts on Leptin: FAQ
The truth about the hormone leptin and obesity.
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.
The problem is that overweight people have large amounts of leptin, but
their brains aren't getting the important signal to stop eating.
"How come the brain doesn't get it? That phenomenon is called ‘leptin
resistance,'" says Lustig, who has done research on the subject. Leptin
resistance is similar to insulin resistance in type 2 diabetes, in which the
pancreas produces large amounts of insulin, but the body doesn't respond to it
Leptin levels can keep going higher as people get fatter. "We all have a
leptin floor; the problem is, we don't have a leptin ceiling," Lustig says.
"In leptin resistance, your leptin is high, which means you're fat, but
your brain can't see it. In other words, your brain is starved, while your body
is obese. And that's what obesity is: it's brain starvation."
Not only is leptin part of the hunger system, it's also part of the reward
system, Lustig says. "When your leptin levels are low, food is even more
rewarding. When your leptin levels are high, that's supposed to extinguish the
reward system so that you don't need to eat so much, and food doesn't look
nearly as good."
But in leptin-resistant people, the reward system doesn't cue a person to
stop eating when leptin levels rise, Lustig says. "The leptin is being made by
the fat cells, the fat cells are trying to tell the brain, ‘Hey, I don't need
to eat so much,' but the brain can't get the signal. You feel hungrier and the
reward doesn't get extinguished. It only gets fostered, and so you eat more and
you keep going and it becomes a vicious cycle. If your brain can't see the
leptin signal, you're going to get obese."
Q. Can leptin work as an obesity treatment?
That was the great hope after leptin's discovery in 1994, says Richard
Atkinson, MD, an endocrinologist, obesity expert, and clinical professor of
pathology at Virginia Commonwealth University.