If you consume excess calories, your body stores them in the form of fat, specifically something called white adipose tissue. But lately you may have been hearing about another kind of body fat, called brown fat (or brown adipose tissue), which is more metabolically active than white fat.
Typically found in small patches in the neck area and along the spine and upper back, brown fat contains a high concentration of energy-producing mitochondria.
Rather than storing calories, it assists in calorie burning. Another type of brown fat, referred to as beige fat, is found marbled among white fat cells. This beige fat seems to have the ability to switch between energy storage and energy burning.
Research into brown fat has accelerated in recent years as scientists look for better ways to treat obesity. The hope is that stimulating brown fat—perhaps through drugs or environmental or nutritional changes—will increase calorie burning. But there are still many unknowns.
The body uses brown fat as a way to produce heat under cold conditions without shivering (shivering is another mechanism that burns calories). Not surprisingly, infants, who can’t shiver, have a lot of brown fat, which helps them maintain normal body temperature. It was thought that this fat vanishes with age, but recent studies have shown that, though it does diminish over time (especially in obese people, unfortunately for them), adults do retain varying amounts of brown fat, which can be activated to different degrees.
If brown fat does play a significant role in energy expenditure, it may help explain some of the differences in people’s tendencies to gain weight (or not), even if they eat and exercise the same amount and are the same height and weight.
Studies in animals, as well as a few in people, have linked increased brown fat to reduced obesity. Still, other factors—notably overeating, lack of exercise, and genetics—play far greater roles in obesity.
Can you boost your brown fat?
As hypothesized in a 2011 paper in Obesity Reviews, the rise in indoor home temperatures in developed countries, thanks to central heating, along with increased time spent indoors and in heated cars, may be contributing to the rise in obesity by causing a loss of brown fat and reduced energy expenditure.
Though biologically plausible, this is just an association and doesn’t prove that central heating causes obesity or that sitting in a cold house will make you lose weight. You’d likely compensate by wearing more clothing.
On the other hand, emerging research backs the idea that exposure to cold stimulates brown fat in some people. For example, a small Japanese study in Obesity in 2011 found that about half of men who sat for two hours in a cool chamber (66°F) in underwear and T-shirts, with their legs on an ice block, showed an increase in brown fat activity.
They also burned 28 percent more calories, equivalent to about 400 calories a day, which was not attributable to shivering. In comparison, men who did not show increased brown fat activity when cold burned only 40 extra calories. No effects were seen at warmer temperatures.
Bottom line: The research on brown fat is intriguing. But whether turning down your thermostat when it’s cold outside will have a significant and lasting effect on body weight has yet to be demonstrated (it will save on energy, though). No dietary supplements are proven to increase brown fat, either. Perhaps one day, drugs will be developed that stimulate it. Until then, however, your best bet for revving up your metabolism and burning more calories is to include some old-fashioned, high-intensity exercise in your workouts.