foodconsumer.org: Your brain on fat -- mechanisms of overeating

Your brain on fat -- mechanisms of overeating
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admin on 09/15/2009 22:18:00
 
By Sheilah Downey sheilahd at foodconsumer dot org
There's a scientific reason it's almost impossible to put down that juicy
hamburger and opt for salad instead.
A specific kind of fat is suspected of zapping people's willpower and even
telling the brain to ignore signals of being full, says a study released today.
The high-fat molecules make their way to the brain and stop the
appetite-suppressing signals from leptin and insulin, hormones that regulate
weight, according to findings from UT Southwestern Medical Center in Dallas.
"Normally our body is primed to say when we've had enough, but that doesn't
always happen when we're eating something good," said senior author Dr. Deborah
Clegg, assistant professor of internal medicine.
Palmitic acid is the high-fat culprit, say researchers, a common saturated fatty
acid found in all the good stuff -- butter, cheese, milk and beef.
Once lured in by the fatty acid, the brain plays dead in a sense, ignoring the
"good" signals from leptin and insulin.
"What we've shown in this study is that someone's entire brain chemistry can
change in a very short period of time," said Clegg. "Our findings suggest that
when you eat something high in fat, your brain gets 'hit' with the fatty acids
and you become resistant to insulin and leptin. Since you're not being told by
the brain to stop eating, you overeat."
Clegg said the effects of the fat "high" last about three days, perhaps
explaining why people who overeat on weekends feel particularly hungry on
Monday.
Science has known for years that a high-fat diet can cause insulin resistance,
but have not pinpointed the mechanism that triggers it, or whether specific
types of fat are to blame.
Because the brain incorporates fat into its structure, Clegg and colleagues
isolated effects of fat on lab rodent's brains for the study. Three types of
fat, palmitic, oleic and monounsaturated, were injected into the rats three
times a day.
Though the results were shown in animals, said Clegg, it reinforces dietary
recommendations to limit saturated fats.
"It causes you to eat more," she said.
The study was published in the Journal of Clinical Investigation.