The Fat-Loving Gene (long)

[Guest guest]

Hi all,

Just ran into this and thought it was worth sharing.

Kathy sen

BMI 58, 352.5 lbs

Surgery scheduled Nov 19th

Dr. Welker

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Article URL: http://www.cbshealthwatch.com/cx/viewarticle/404883

Article Level: Advanced

The Fat-Loving Gene

Nada Mangialetti, Medical Writer

Introduction

Ever wonder why, once you take that first mouthful of premium Rocky

Road ice cream, it's hard to stop until your spoon is scraping the

bottom of the half-gallon carton?

Despite what you've heard, it may not be simply because you're weak-

willed or suffering from some deep-seated psychological problem.

Scientists are finding that the roots of out-of-control eating may

have more to do with your genes and your body chemistry than with

your mind.

Scientists are finding that out-of-control eating may have more to do

with your genes and your body chemistry than with your mind.

Leibowitz, PhD, associate professor of behavioral neurobiology

at Rockefeller University in New York, has observed that when rats

eat fat-laden food, the resulting increased level of triglycerides in

their blood triggers the activation of certain genes. These genes

produce large amounts of a peptide, or protein, called galanin in the

nerve cells of the hypothalamus, a gland hidden deep in the brain.

According to Leibowitz, galanin, whether produced naturally by the

body or injected into particular areas of the hypothalamus,

stimulates feeding behaviors--specifically, eating fats.

In other words, the rats eat more and more of the very stuff that

causes them to eat more and more. Scientists call this a " positive

feedback loop. " Dieters call it " being out of control. "

Galanin's Gotcha

Galanin packs a quadruple-whammy punch. Besides increasing the amount

of fat you eat, it also seems to decrease the amount of energy your

body uses and lessens the activity of the sympathetic nervous system.

That's the part of your nervous system that, in the face of danger,

automatically makes you alert and ready for " fight or flight. " No

wonder you feel lazy after downing a half-gallon of ice cream!

Normally, the hypothalamus signals the brain when the stomach is

full. But galanin in the hypothalamus blocks that signal.

Galanin also dulls the sensation of satiety, or fullness. Normally,

the hypothalamus gland signals the brain when the stomach is full.

But galanin in the hypothalamus blocks that signal. It's not yet

known exactly how galanin does this. " That's what we're trying to

explore, " says Leibowitz.

The result is fewer calories burned while more calories are coming

in.

People seem to like full-fat dairy products, oil-soaked chips, and

fatty meats more than low-fat foods. Animals, however, do not

naturally prefer fat-laden food, nor do they ordinarily have access

to it. " There's not a lot of fat in the wild, " says

Leibowitz. " Animals don't normally get fat. "

So in order to study rats whose food preferences are more like those

of humans, Leibowitz sometimes uses rats that have been specially

bred to prefer fat-laden food. She finds that when these fat-loving

rats eat fatty foods, they produce more galanin than rats that don't

have that preference.

People who have a " fat tooth " may also be genetically predisposed to

prefer fat. Or, they may have learned to prefer fatty foods because

these foods are so much a part of the modern Western diet. " We don't

know, " says Leibowitz. It may be simply because, as she puts

it, " Fats just make foods taste better. " Whatever the reason for

preferring fatty food, people who do, like the fat-loving rats, may

be the very people who are most sensitive to it.

The Triglyceride Test

For normal-weight rats that are usually fed a low-fat diet, a blood

test after a single high-fat meal can determine which rats have the

highest levels of triglycerides in their blood. Those that do are

more likely to produce large amounts of galanin when they eat fat,

and, according to Leibowitz, are more likely to become obese. So far,

no one has conducted this test on humans. " It really should be done, "

says Leibowitz.

Some people may absorb fewer triglycerides from the fat that they eat

and thus have less active galanin-producing genes.

If Leibowitz's findings prove true, people who put their spoon down

after three little licks of ice cream, saying, " I just don't want any

more, " may not necessarily be exerting greater willpower or

displaying greater mental health than their bottom-of-the-carton-

scraping friends. They may simply be absorbing fewer triglycerides

from the fat that they eat and thus have less active galanin-

producing genes. With less galanin in the hypothalamus, eating a few

mouthfuls of fat will not result in an escalating positive feedback

loop and an empty ice cream carton.

In contrast, people who can't put their ice cream spoon down after

that first mouthful may be absorbing more triglycerides and so have

more active galanin-producing genes--thus the feeling of losing

control.

It was already known that triglycerides, which abound in fatty foods,

enhance the storage of fat in tissue and upset the delicate balance

of glucose metabolism in the muscles and liver. But only at the 2001

meeting of the American Association for the Advancement of Science

did Leibowitz first present her research about the additional

intermediary role of triglycerides in the production of galanin and

the resulting tendency to eat more fat. She is in the process of

preparing her findings for submission to a professional journal so

that her science colleagues can review it.

If Leibowitz's research can be confirmed by other scientists and

replicated in humans, you can stop blaming yourself for your " lack of

control " around fat-laden foods. In the future, you may be able to

take a blood test to find out whether you are especially fat-

sensitive.

Sidebar: The Skeptical View

Flier, MD, an endocrinologist and Harvard faculty dean for

academic affairs at Beth Israel Deaconess Medical Center, is

skeptical. " Dr. Leibowitz has been interested in galanin for a while

because of her suggestion that it induces a particular taste for

fat, " he says. " A lot of other people in the field are a lot more

reserved. "

Flier points out that scientists know of " at least ten to 15 " other

neuropeptides in the hypothalamus--any one of which, or perhaps some

combination--can cause changes in the eating behavior of animals when

injected into the brain. He says he doubts that the relation between

galanin and eating fat is as straightforward as Leibowitz's research

might indicate. And while it's simple to give food and then measure

triglycerides in the blood, he says that it is impossible to directly

observe what is going on in the hypothalamus--at least in humans.

Flier says that it's not yet clear that galanin is the culprit. " Many

other things are also changing that she's not measuring, " he says.

If a molecule could be designed that would cancel out the action of

galanin, and if that molecule also decreased a person's tendency to

eat fat, then, Flier acknowledges, Leibowitz's findings might be more

compelling. Indeed, pharmaceutical companies are trying to develop

exactly such types of drugs to act as " antagonists " to many

neuropeptides. Alternatively, Flier says that he might be convinced

of the role of galanin, triglycerides, and fat " if we find that

people who are fat or love to eat fat have mutations in their genes "

that cause them to produce more galanin than normal.

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Nada Mangialetti is a freelance science writer for CBS HealthWatch by

Medscape. She is also a licensed clinical psychologist.

Reviewer: Beth Israel Deaconess Medical Center. Reviewed for medical

accuracy by physicians at Beth Israel Deaconess Medical Center

(BIDMC), Harvard Medical School. BIDMC does not endorse any products

or services advertised on this Web site.