Researchers have identified hormones that help the body rev up heat during shivering.

Researchers at the Garvan Institute of Medical Research and colleagues found that hormones Irisin and FGF21 help muscles and fat communicate with each other when we shiver or do moderate exercises. This communication eventually leads to the conversion of white "energy-storing" fat into brown "energy-burning fat."

Calorie-burning brown fats help humans maintain core body temperatures in cold weather. Understanding the mechanism could lead to newer therapeutics that fight obesity, according to a news release from the Virginia Commonwealth University School of Medicine,

Hormones Irisin and FGF21

According to Dr Paul Lee, one of the study authors, cold exposure and moderate exercise lead to an increase in the levels of hormone irisin (produced by muscle) and FGF21 (produced by brown fat).

In their lab study, the rise in the level of irisin during 15-20 minutes of shivering was roughly equal to the rise in hormone seen after an hour of moderate exercise. Both hormones (irisin and FGF21) worked together to convert white fat into brown fat in about six days.

For the present study, researchers exposed volunteers to a cold environment of 18 to 12 degrees. They then obtained blood samples from participants and detected shivers using skin sensors.

"We identified two hormones that are stimulated by cold - irisin and FGF21 - released from shivering muscle and brown fat respectively. These hormones fired up the energy-burning rate of human white fat cells in the laboratory, and the treated fat cells began to emit heat - a hallmark of brown fat function," Lee said in a news release.

The Good Brown Fat

Previously, it was believed that brown fat, which helps maintain body temperature, was present only in babies. However, recent studies have shown that the calorie-burning fat can be found in some humans, especially lean people.

There has been a lot of research in understanding how brown fats burn energy and how these cells can be used to fight obesity. Back in 2010, Yu-Hua Tseng at Harvard Medical School and colleagues showed that it is possible to convert muscle cells and white fat cells into brown fat.

Recently, researchers from Netherlands showed how exposure to moderate cold could lead to weight loss.

"Excitement in the brown fat field has risen significantly over last few years because its energy-burning nature makes it a potential therapeutic target against obesity and diabetes," said Lee in a news release. "White fat transformation into brown fat could protect animals against diabetes, obesity and fatty liver. Glucose levels are lower in humans with more brown fat."

The study is published in the journal Cell Metabolism.