Can brown fat be used to ‘cure’ obesity? Or is it the new weight-loss buzzword, no less a fad than multivitamins and protein diets that end up causing more harm than good?
The answer to both questions is ‘maybe’ — based on the most current information scientists have at hand, including the results of two recent studies on brown fat.
Brown fat, the brown-colored fatty tissue found mainly in patches along the neck and between the shoulders of newborn mammals and in adults of hibernating animals, exists to warm the body.
Unlike ordinary fat cells that burn glucose to power various life processes, brown fat cells directly release as heat the energy they get, in a process known as “nonshivering thermogenesis.”
For a long time, scientists thought brown fat was found only in rodents that don’t shiver and need the heat-generating brown fat to keep warm.
A key survival mechanism for some animals living in cold environments — as well as newborn babies — brown fat allows the body to keep warm without depleting precious energy stores, which happens when muscles shiver in the cold.
Scientists thought that adult humans, who shiver and had no need for brown fat, did not have it.
But three years ago, three separate teams of researchers, working independently, found brown fat in adults. Brown fat showed up in scans of people wearing light clothes like hospital gowns in cold rooms.
Just a few ounces of brown fat in the upper back, on the side of the neck, in the dip between the collarbone and the shoulder, and along the spine showed up in scans detected brown fat absorbing glucose.
Now, a recent study from Canadian researchers shows that cold triggers one form of brown fat to burn calories like a furnace, sucking fat out of the rest of the body to fuel itself.
Another new study from Dana-Farber Cancer Institute, in Boston, Massachusetts finds that exercise can convert ordinary white fat into a second form of brown fat.
Brown fat burns calories
In the first study, researchers from Quebec, Canada’s University of Sherbrooke embarked on a study to find out if the brown fat detected in previous studies by scans in adult humans burned calories to raise body temperature — as it did in mice and hibernating animals.
Just because studies showed the brown fat in adults taking up glucose did not mean it burns calories, researchers of a previous Swedish study on brown fat note.
“We did not know what the glucose actually did: Glucose can be stored in our cells, but that does not mean that it can be combusted,” says Barbara Cannon, author of the earlier study.
Setting out to find answers to this questions, a team led by Dr. André Carpentier, an endocrinologist at Quebec, Canada’s University of Sherbrooke, recruited six healthy men ranging from 23 to 42 years old.
The men were then kept chilled by cold temperatures—but not to the point of shivering, which burns calories. Researchers then used a different kind of medical scan to show the metabolism of fat.
What Dr. Carpentier’s team found was that brown fat burns white fat to create heat. Their findings are published in late January in The Journal of Clinical Investigation.
Their study also showed that glucose is not a major source of fuel for brown fat cells — instead brown fat can burn ordinary fat and when brown fat cells run out of their own small repositories of fat, they suck fat out of the rest of the body.