April 9, 2009

Cold-Activated ‘Brown Fat’ May Aid In Weight Loss

Three studies published Thursday find that the thinly-spread, so-called brown fat that helps keep newborns warm is more common in adults than previously believed. 

Once cold temperatures activate the brown fat, it burns calories faster than regular fat -- a discovery that could lead to improved weight-loss treatments, researchers said on Wednesday.

Since brown fat is typically so dormant in adults, scientists have long debated whether it was even present at all. 

But the three studies, published in Thursday's New England Journal of Medicine, found that brown fat is indeed present in most adults and can be detected by exposing it to cold temperatures.   In some cases, adults with more active areas of brown fat were thinner, the studies found.

Scientists hope that people could burn off extra calories without exercise if a way can be found to activate this brown fat and get the body to make better use of it.

"Fifty grams of maximally activated brown fat accounts for 20 percent of your resting energy expenditure," Dr. Aaron Cypress of the Joslin Diabetes Center in Boston, one of the study's leaders, told Reuters.

"If you add that up, that's 400 or 500 calories per day."

"Practically speaking, we have a great potential to have a new treatment in our armamentarium against diabetes and obesity."

Dr. Kirsi Virtanen of the University of Turku in Finland and his team used positron emission tomography, or PET scans, to identify active brown fat deposits in five study participants, and obtained tiny samples of both types of fat.

They found that the brown fat became more active when the participants were cold.

"If the brown adipose tissue in this example were fully activated, it would burn an amount of energy equivalent to approximately 4.1 kg (9 pounds) of adipose tissue over the course of a year," the researchers wrote in a report about the study.

Meanwhile, a team of researchers at Maastricht University Medical Center in the Netherlands discovered that obese men had less brown fat than lean men.

"Taken together, these studies point to a potential 'natural' intervention to stimulate energy expenditure: turn down the heat and burn calories (and reduce the carbon footprint in the process)," wrote Dr. Francesco Celi of the National Institute of Diabetes and Digestive and Kidney Disease in a commentary.

However, he cautioned that the conclusion might be oversimplified.

Cypress said experts must first find a way to activate the brown fat and maybe even persuade the body to make better use of it. 

The current research did not directly examine whether activating this fat would make people lose weight, and further research may find that even if the brown fat is activated, the body may compensate by eating more, he said.

"If you think about it, if you eat three donuts, you hit that calorie count right there," Cypress told Reuters.

"Using brown fat to treat obesity has been talked about for 30 or 40 years," he said.

"But people essentially gave up on it. Many said it didn't exist in adult human beings and many said it didn't have any connection to obesity and weight at all. What these studies show is that virtually every adult human being has functional brown fat in them."

The three studies were published in Thursday's New England Journal of Medicine.


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