newe by www.mrchat.net
Want another reason why you shouldn't spend too much time at the
trough? Because consistently eating too much food over a period of
just a few weeks can screw up your brain, taking away your ability to
control your appetite.

That's the basic finding in a new study out of the University of
Wisconsin-Madison that could help explain why once you've put on those
extra pounds, it's really hard to take them off. The study is
published in the current issue of the journal Cell.

"We've discovered why the appetite doesn't shut down," said Dongsheng
Cai, assistant professor of physiology at UW-Madison, in a telephone
interview, even after a person has consumed enough food to maintain
the correct balance between calorie intake and energy expended.

The answer lies in a normally inactive "pathway" through a critical
part of the brain that springs to life after at least a couple of
months of "overnutrition," he said. A pathway is a course by which
brain cells transmit impulses from their origin to their destination.
But in this case, a normally dormant pathway is re-energized and
interferes with "signaling" that should tell the brain you've had
enough to eat.

"We're not talking about one day, or even a few days" of overeating,
Cai said. "It's not too long. Two or three months of overnutrition, a
diet high in fat and sugar," can wake up the pathway, he said.

Once the pathway is mobilized, he said, it can "lead to a number of
dysfunctions, including resistance to insulin and leptin." Leptin is a
fat hormone essential for appetite control. Insulin lowers blood sugar
by causing cells to extract it from the bloodstream. Both are critical
to maintaining the balance between caloric intake and energy
expenditures.

The good news is it may be possible to shut down that apparently
obsolete pathway in the brain, thus restoring an obese person's
ability to control his or her appetite. It's significant that the
activation of the pathway preceded obesity in lab mice, so it is
clearly part of the cause of weight gain, not just the result.

"These experiments and results indicate that oversupply of general
nutrients can acutely activate the hypothalamic [pathway] before the
onset of obesity," the study says.

Cai and his colleagues have focused their research on the
hypothalamus, the part of the brain that for the past 10 to 15 years
has been recognized as the brain's "headquarters" for maintaining an
energy balance. They used lab mice for their research, since it's not
practical to dissect human brains after an extended period of
overeating, but they are confident the findings will apply to humans
as well.

"Many pathways established in animals are exactly the same in humans,"
Cai said.

The same type of pathway actually plays a critical role throughout the
entire body's immune system, but it has no known function in the
hypothalamus. Cai speculates that it may be a remnant from an ancient
immune system that is no longer active.

In their paper, the researchers identify the pathway as "a master
switch and central regulator" of the body's immune system, so just
simply turning it off would be disastrous. The challenge is to come up
with a way, possibly medication or genetic engineering, to keep the
pathway alive for the immune system, but keep it dormant in the
hypothalamus, where apparently all it does is cause trouble. That
could take years, of course, even assuming the basic findings are born
out by further research.

The research indicates that the critical signaling function of two
hormones, insulin and leptin, is disrupted when the pathway in the
hypothalamus is activated.

"Insulin is a hormone secreted by the pancreas, and leptin is another
type of hormone secreted by fat tissue," Cai said. "When we have
obtained enough calories, these two hormones travel to the brain and
tell the hypothalamus it's time to stop eating, you have enough
calories.

"But these two message systems can be interrupted by the activation of
the pathway we've discovered, so the appetite doesn't shut down," he
said.

It's also likely that the message telling the brain to increase energy
expenditure is also shut down, Cai said. So, instead of going out and
walking off those excess calories, the dieter takes a nap.

That plunges the person into a downward spiral, eating more and more,
and putting on more and more pounds. The sentinels that are supposed
to maintain the correct balance between caloric consumption and energy
expenditure remain silent, deactivated by the reactivation of a part
of the brain that shouldn't be there.

"Our work marks an initial attempt to study whether inhibiting an
innate immune pathway in the hypothalamus could help to calibrate the
set point of nutritional balance and therefore aid in counteracting
energy imbalance and diseases induced by over-nutrition," the report
states.

In other words, maybe there's a way here to reset the appetite and
make it a lot easier to knock off those extra pounds. The research
also suggests that in some cases, there's more at work than simply a
lack of willpower when it comes to losing weight.

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