The Slimming Hormone

Dieters who persevere with exercise and diet may get help from the hormone leptin.

By Hara Estroff Marano, published on April 28, 2004 - last reviewed on November 20, 2015

We all know it takes motivation to keep focused on goals, such as
to eat better and get more exercise. The good news is that a little bit
of effort can boost motivation by setting big rewards in motion.

A study conducted at the University of Florida suggests that
dieters who persevere long enough to lose a few pounds may get help from
a hormone that's otherwise stifled by excess fat.

In the study, adult rats fattened on a
high-calorie diet returned to their original weights when scientists
delivered the "slimming hormone," called leptin, to the rodents' brains. According
to Dr. Satya Kalra, a professor of neuroscience, leptin is produced by
mammals, including you and me.

The findings suggest that some day, the hormone could eventually
provide better weight-control methods. For now they indicate that
unwanted pounds are best fought with persistence and prevention.

"The take-home message is it's very important that we
maintain a healthy lifestyle," says Kalra, "That includes a
lot of energy expenditure through exercise and tight control on calorie

Leptin, produced in our fat cells, helps regulate energy use by
signaling the brain to reduce appetite and burn more calories. But
there's a caloric Catch-22: Overweight animals produce excess leptin, so
much that it impairs the very mechanism that should eliminate excess

For reasons that are not clear yet, when leptin levels are
increased in the blood, leptin is ineffective in performing its normal
function. Scientists call this "leptin resistance." "It
increases more quickly if the animal consumes a diet that's very rich in
calories," says Kalra.

For several years, he and his colleagues have sought to get around
leptin resistance in animals by delivering leptin-producing genes to the
hypothalamus, an area of the brain that controls many basic body
functions. It's where the body's feeding center is located.
They focused on a tiny portion of the hypothalamus called the
paraventricular nucleus. That's where assorted brain chemicals act
to stimulate or inhibit appetite and it's the home of neural
circuits that increase energy expenditure.

In the study, a group of animals were made obese on a diet made up
of 45 percent fat. After 80 days, they weighed 20 percent more than a
group of animals fed a normal diet of 11 percent fat.

Then the obese animals were given a shot of leptin-producing gene
into the paraventricular nucleus. Fifty-six days later, those that
received the leptin gene were now only 3 percent heavier than they were when
the experiment began.

Kalra thinks that in the fat rats there's some kind of
insufficiency of leptin in the brain areas where leptin normally
works—just as there is in 95 percent of dieters. There's no magic
pill for easy weight loss, but exercise and good nutrition are as
reliable as ever, Kalra says. "It's important to emphasize

And you are definitely not alone. Currently, almost 59 million
Americans are considered obese, with a body mass index of 30 or more,
based on excess fat in relation to lean body mass.

So start the ball rolling—literally—and your leptin
will begin leaping to your defense.