Brown fat could explain why some stay toasty in the cold
Angela Mulholland, CTVNews.ca
Published Tuesday, January 24, 2012 1:32PM EST
Canadian researchers may have discovered why some people are able to stay warm in cold temperatures: more brown fat. And it's a finding that might one day be used a tool in the fight against obesity.
Brown fat is a kind of "good fat" that researchers are only just beginning to understand.
Unlike white or yellow fat, which gathers around our waists and thighs, brown fat seems to be concentrated around the front and back of the neck. While our white fat helps store excess calories, the brown kind appears to burn through calories, to generate heat.
Rodents and newborn humans have lots of brown fat, which explains why they don't shiver when they're cold. Overweight people, those with diabetes, and older people appear to have less of it.
So far, it's not known if it's possible to boost one's brown fat reserves. So instead, researchers have focused on how to "turn on" brown fat, to activate it so it burns fat. And the key seems to be cold.
In a new experiment, published in the Journal of Clinical Investigation, Quebec researchers discovered that when healthy adults were exposed to a little bit of cold, their brown fat revved into gear.
For the experiment, Dr. André C. Carpentier an endocrinologist from Universite de Sherbrooke helped recruit six younger healthy men, some of whom were of normal weight, some overweight and some obese.
The researchers measured how much brown fat the men had and then placed them into cooling suits. They lowered the temperature so that the men's skin temperature fell by 3.8 degrees Celsius, but their core temperature remained essentially the same.
"During this exposure, these patients were slightly shivering. They were at the threshold of shivering," Dr. Carpentier explained to CTV News.
They found that the more brown fat each man had, the colder he could get before he started to shiver. They also found that once the men were chilly, their brown fat was activated, helping to burn calories.
"During that period we measured how many calories their body was burning," said Carpentier. "And we found there were about 250 extra kilocalories burned over three hours."
That's about 1.8 times more calories than the men would have burned if they had simply been resting. It's also almost equivalent to the amount of calories they would have burned if they'd gone for a walk.
The researchers concede their study, which was funded by the Canadian Diabetes Association, was quite small.
"Despite this limitation, we are nonetheless confident that our findings apply to other populations, since they were very consistent between subjects," they write.
The finding is a major step, say the researchers, but what it might mean isn't clear.
"It remains to be demonstrated whether chronic and frequent bouts of cold exposure may contribute to increase (brown fat) capacity," the authors write.
Carpentier says there is still much research to be done on what this might mean for weight loss.
"We still don't know if activating it (brown fat) is a good idea or not and whether it will work to treat obese people or people with type 2 diabetes. "So it is still premature to use that as a therapeutic target for (obesity)," he said.
He also doesn't recommend people deliberately chill themselves in a bid to lose some weight.
"It is still too early to cool yourself in a suit and in the hope that you will lose weight because we don't know how the body adapts over the long run to this type of stimulation, whether these stimulations can increase appetite or change the metabolism of the body over time," he said.
With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip