Unlike more recognizable white fat, which stores surplus energy, brown fat burns energy to generate heat.
Newborn babies have brown fat -- presumably to help regulate their body temperature -- but adults are believed to have little.
Researchers have studied brown fat for several decades in the hope that unlocking the mysteries of the unique fat could result in treatments to speed up metabolism and promote weight loss .
Two new studies to be published tomorrow in Nature may bring them closer to that goal.
"I really do believe that promoting brown fat growth is a plausible approach to weight control," researcher Bruce Spiegelman, PhD, of Harvard University's Dana-Farber Cancer Institute, tells WebMD. "To me it is attractive because of its simplicity. If more of our fat were brown fat, the mouse studies suggest that we would be leaner and better able to resist obesity."
Brown Fat Derived From Muscle
In earlier research, Spiegelman and colleagues identified what he calls a "master switch" in mice, which promotes the production of brown fat.
In their latest animal studies, the researchers showed that the molecular switch, known as PRDM16, regulates the creation of brown fat from immature cells and that knocking out PRDM16 turned them into muscle cells.
"We showed that brown fat and white fat have completely different origins," he says. "Brown fat is derived from muscle. That was a huge surprise."
In the second study, researchers from Harvard's Joslin Diabetes Center described a different trigger for brown fat.
Yu-Hua Tseng, PhD, and colleagues identified the protein BMP-7, which is known for promoting bone growth, as a growth factor for brown fat.
In mouse studies, the researchers found that mice genetically altered to have no BMP-7 protein had less brown fat as they developed than non-altered mice.
And developing mice treated with BMP-7 ended up with more brown fat than untreated mice and had greater energy expenditures.
Tseng tells WebMD that her lab is now studying the impact of long-term BMP-7 induction on body composition of mice.
"The hope is that this research will lead to better ways to treat obesity, especially for people who are overweight because of their genes," Tseng says. "Right now, there are not many good options for these people."
Brown Fat: Unanswered Questions
In an editorial accompanying the two studies, obesity researcher Barbara Cannon, PhD, of Stockholm University, noted that while the two studies answer some questions about the production of brown fat, they raise others about the role of BMP-7 and PRDM16 in obesity and weight control.
"Answers to these questions would take us a step closer to the ultimate goal of promoting the brown fat lineage as a potential way of counteracting obesity."
Spiegelman tells WebMD that he believes obesity treatments that promote the production of brown fat could be a reality in as little as a decade.
"We know that we can stimulate the production of brown fat in mice," he says. "It is not unreasonable to think that we can also do this in humans."
By Salynn Boyles
Reviewed by Louise Chang
©2005-2008 WebMD, LLC. All rights reserved