Brown fat, also known as brown adipose tissue (BAT) is one of two types of fats found in humans, the other two being white or yellow fat. Hibernating mammals and newborns have especially high levels of brown fat. Its main function is to generate body heat in animals and newborns. White fat cells (adipocytes) contain a single lipid droplet, as opposed to brown adipocytes, which contain several smaller lipid droplets and a considerably higher number of iron-containing mitochondria. The high iron is said to give brown fat its brown color. There are more capillaries in brown fat than white fat, because its oxygen requirement is greater.
White fat accumulates around the waist and thighs, while brown fat appears to be concentrated in the front and back of the neck.
Experts say much remains to be known regarding brown fat, but the main differences between these two types appear to be:
Brown fat burns through calories in order to generate heat
White fat is a storage area for excess calories
Rats, mice and human newborns do not shiver when they are cold because they have higher levels of brown fat. Obese individuals, as well as those with diabetes type 2, have less brown fat than other people.
Scientists do not yet know how humans might be able to increase the amount of brown fat in their bodies. In this study, endocrinologist, Dr. André C. Carpentier, from Universite de Sherbrooke, and team set out to determine how humans might be able to switch on the brown fat so that it uses up fat. They found that exposure to cold temperatures seems to be the best trigger.
They found that when healthy adult volunteers were exposed to even slightly cold environments, their brown fat “turned on”.
The team enrolled six healthy young men, whose weights ranged from normal, overweight to obese. An obese person has a BMI (body mass index) of at least 30.
All the participants had their brown fat levels measured before the experiment began. They were then placed into cooling suits which lowered the temperature of their skin by 3.8 Celcius. However, their core body temperatures stayed pretty much the same.
In an interview with CTV News, Dr. Carpentier said:
“During this exposure, these patients were slightly shivering. They were at the threshold of shivering.”The researchers found a link between levels of brown fat and when people started to shiver from cold.