Researchers have found that exposure to cold temperatures
may prompt unhealthy fats to become healthy fats, but obesity and inflammation
may blunt the effect.
Cold temperatures may prompt unhealthy white fat in the
thighs and belly to turn into brown fat that burns calories for body heat, a
new study says.
But being obese appears to hinder this process, according to
researchers.
Most adult fat deposits are what's known as white fat, and
it was once believed that only babies have brown fat, which appears to help
keep them warm.
Previous research suggested, however, that adults also have
some brown fat. Then a study published in 2012 by researchers at Harvard
determined that the brown fat found in adults isn't the same as brown fat in
babies.
Brown fat in babies arises from muscle, but brown fat in
adults is actually a "beige" fat that occurs from the
"browning" of white fat, the Harvard team explained.
For the new study, a team of researchers led by Dr. Philip
Kern of the University of Kentucky School of Medicine compared belly fat taken
from 55 people during the summer and the winter. They also examined thigh fat
collected from 16 people after they held an ice pack on their skin for 30
minutes.
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Belly fat taken from people in the winter had higher levels
of two genetic markers for brown fat than belly fat collected in the summer,
the study found.
The thigh fat taken after people placed an ice pack on their
skin also had higher levels of three genetic markers linked with brown fat, the
researchers reported.
However, these brown fat-producing effects were blunted in
obese people, according to the study released Oct. 9 in the Journal of Clinical
Endocrinology & Metabolism online.
"We wanted to investigate whether human adults had the
ability to transform some white fat deposits into beige fat when they were
exposed to cold," Kern said in a journal news release.
"Browning fat tissue would be an excellent defense
against obesity. It would result in the body burning extra calories rather than
converting them into additional fat tissue," he added.
Kern said the findings "indicate inflammation can
hinder the conversion of white to beige fat."
Prior research has shown that brown fat prevents obesity in
rodents, according to the researchers. And several past studies have suggested
that cooler temperatures may help burn calories in humans, including one study
that suggested the effect might be linked to brown fat.
But for now, the research is preliminary and experts say
it's too soon to know if cold temperatures would have much of an effect on
weight in people.
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