Shivering and exercise may stimulate the conversation of energy-storing 'white fat' into energy-burning 'brown fat', suggests study.
Around 50 g of white fat stores more than 300 kilocalories of energy. The same amount of brown fat could burn up to 300 kilocalories a day.
Endocrinologist Dr Paul Lee, from Sydney's Garvan Institute of Medical Research, recently undertook the study at the National Institutes of Health (NIH) in Washington*, funded as an NHMRC Early Career Research Fellow.
His work uncovered a way that fat and muscle communicate with each other through specific hormones - turning white fat cells into brown fat cells to protect us against cold.
Dr Lee showed that during cold exposure and exercise, levels of the hormone irisin (produced by muscle) and FGF21 (produced by brown fat) rose. Specifically, around 10-15 minutes of shivering resulted in equivalent rises in irisin as an hour of moderate exercise. In the laboratory, irisin and FGF21 turn human white fat cells into brown fat cells over a period of six days. The study is now published in Cell Metabolism
We are all born with supplies of brown fat around our necks, nature's way of helping to keep us warm as infants. Until only a few years ago, it was thought to vanish in early infancy, but we now know that brown fat is present in most, if not all, adults. Adults with more brown fat are slimmer than those without.
"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 Dr Lee.
"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."
In the current study, Lee set out to understand the mechanism underlying the activation of brown fat. It was already known that cold temperatures stimulate brown fat, but was unclear how the body signals that message to its cells.