Can Brown Fat Make You Thin?

April 8, 2009 -- By activating the brown fat in your body, you could lose 9 pounds or more of bad white fat every year -- without having to eat less or exercise more.

Until recently, scientists thought adults didn't have brown fat. They thought it was there to help babies keep their bodies warm and went away as the body became more muscular.

But three new studies in the New England Journal of Medicine now show that more than half of adult men and women have enough brown fat in their bodies to burn off substantial amounts of white fat -- if the brown fat somehow is stimulated.

For example, Kirsi A. Virtanen, MD, PhD, of the University of Turku, Finland, and colleagues analyzed brown fat in five young men. One of the men had about 2.2 ounces of brown fat.

"If the brown [fat] in this example were fully activated, it would burn an amount of energy equivalent to approximately 4.1 kilograms [9 pounds]" of fat over the course of a year, the researchers calculate.

And that's a low estimate, as this assumes only 50% activation of the brown fat.

Brown Fat and Health

Scientists became aware of brown fat in adults because it's a problem for PET scans. Activated brown fat shines brightly in the scans, making it hard for doctors to see what they're looking for. Technicians have come up with several ways -- such as giving patients beta-blocker drugs -- to prevent brown fat activation.

As researchers looked into the mysteries of brown fat, they found that it is more closely related to muscle than to white fat. And recent studies suggested it might be possible to make the body produce more brown fat.

How does it work? Brown fat becomes activated when you're cold. Virtanen and colleagues took advantage of this in their study: The five volunteers underwent PET scans after spending two hours under-dressed in a cold room, with one foot soaking intermittently in a bucket of ice water.

Activated brown fat burns white fat as fuel. It's a very inefficient process that gives off heat -- and consumes a lot of fat.

New studies by Wouter D. van Marken Lichtenbelt, PhD, and colleagues at the University of Maastricht, Netherlands; and by Aaron M. Cypess, MD, PhD, of Beth Israel Deaconess Medical Center, Boston, and colleagues show that:

• Obese people have less brown fat than lean people do.
• Men have less brown fat than women do.
• Older people have less brown fat than younger people do.
• People with high blood sugar have less brown fat than people with normal blood sugar.

"In other words, they found a direct correlation between the activation of brown adipose tissue and metabolic measures that indicate the presence or absence of good health," NIH researcher Francesco S. Celi, MD, writes in an editorial accompanying the studies.