The World Health Organization estimates that over 1.4 billion adults and over 40 million children under the age of five are overweight or obese. Excess body weight can lead to type 2 diabetes, heart disease, infertility, cancer and neurodegenerative disease, and unhealthy weight is associated with one in five American deaths. However, new research has found that it could be possible to stimulate brown fat to burn calories or convert white fat to brown fat, reducing body weight. Thorsten Gnad of the University of Bonn in Germany is the lead author of the paper published in Nature.
There are two main types of adipose (fat) in mammals: brown and white. White fat is stored energy and is the fat that adds bulk to the body. Brown fat—which is more metabolically active—does the opposite, and uses energy in the body to generate heat and regulate body temperature. Brown fat is most plentiful in hibernating animals and newborns, but adults do have brown fat as well. White fat can make up a considerable portion of a healthy body weight (20% in males, 25% in females), but brown fat is much less bulky and represents 3-7.5% of an adult’s body weight. Brown fat levels can be boosted through exercise.
"Not all fat is equal," said senior author Alexander Pfeifer in a press release. “If we are able to activate brown fat cells or to convert white fat cells into brown ones, it might be possible to simply melt excess fat away.”
Researchers have known for years that the body is able to convert white fat into brown fat, and have been exploring mechanisms responsible for making the switch. For this study, the team explored an adenosine receptor in brown fat called A2A. Adenosine is released when the body is stressed, and then picked up by the brown fat, which then begins energy production.
"If adenosine binds to this receptor in brown fat cells, fat burning is significantly stimulated," Gnad explained.
White fat cells, on the other hand, lack this adenosine receptor. The team removed a gene for the A2A adenosine receptor from brown fat in mice and put it in the white fat cells. This effectively “browned” the white cells, allowing them to begin burning fat, creating energy.
Previous studies have attempted to use adenosine to activate the brown fat in rats and hamsters, but found that adenosine blocked brown fat activity instead of triggering it. It was then assumed that this pathway would never work. However, Gnad’s team learned that the brown fat found in mice and humans reacts differently.
Still, the knowledge gained in this study raised a number of questions and is a long way off from being used to create a clinical treatment for combating obesity and its associated diseases. The A2A receptor is not the only mechanism being explored to stimulate brown fat.
Earlier this month, a team from Yale Medical School published a paper in Cell in which they describe how they stimulated mouse brains into converting white fat into brown fat. They also found that the brain fears food deprivation more than it fears the body freezing to death, which is why more white fat isn’t naturally browned by the brain. However, now that modern life allows for minimum work for obtaining maximum calories, the brain could be retrained to let more of that white fat go.