Cold helps body turn bad fat into good fat

WASHINGTON, Oct. 10 (UPI) -- Most mammals, including humans, have two types of fat -- white fat and brown fat, sometimes called bad fat and good fat, respectively. Understanding the differences between the two, new research suggests, could help people lose weight.

White fat acts as a thermal insulator, keeping body temperatures stable. It's the thin layer of blubber most obvious on the human belly and thighs. In healthy people, white fat makes up no more than 20 to 25 percent of the body's weight.

Brown fat, on the other hand, is less abundant and doesn't trap but creates heat, thus warming a cold body by burning energy, or calories. When white fat takes on brown fat characteristics, the process is called "browning" and the resulting fat is known as "beige fat." Babies and hibernating mammals typically possess more brown fat than do adults.

Because beige and brown fat are able to burn calories, they are a positive force for weight loss. An excess of white fat is associated not with weight loss but weight gain -- and with obesity. Now, researchers say something as simple as applying an ice pack to white fat deposits for 30 minutes could encourage the so-called browning process and help instigate weight loss.

"We wanted to investigate whether human adults had the ability to transform some white fat deposits into beige fat when they were exposed to cold," study author Dr. Philip A. Kern, a researcher of the University of Kentucky School of Medicine, said in a press release. "Browning fat tissue would be an excellent defense against obesity. It would result in the body burning extra calories rather than converting them into additional fat tissue."

In taking biopsies of patients' fat deposits, scientists found that belly and thigh fat in the winter showed greater signs of browning than did fat samples taken in the summer -- suggesting cold temperatures facilitate the transformation of white fat into beige. Applying ice packs to fat deposits had similar transformative effects.

Unfortunately, the positive fat-browning effects of the cold were diminished in obese patients when compared to healthier study participants.

"Our findings indicate inflammation can hinder the conversion of white to beige fat," Kern said. "When we analyzed tissue samples in the lab, we found that exposing white fat to macrophage cells from the immune system inhibited the transformation."

Still, increased exposure to the cold could help people keep the weight off and mitigate obesity issues. Researchers suggest more people try turning down their thermostats for a few hours each day during the winter. The new study was published this week in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.