Oct. 22, 2014 -- Dropping extra pounds has long been a goal for people who want to improve their health and appearance. But a different type of fat -- called brown fat -- may help us lose weight.
Researchers recently found that cold temperatures may help us make more of this “good fat” that can boost our metabolism and burn calories.
We asked experts to weigh in on the potential benefits.
What is brown fat?
It's a type of body fat that creates heat. It's reddish-brown in color because it's packed full of the power producers in cells, called mitochondria, which give cells energy by turning calories into heat.
"Everyone is born with brown fat. Babies have an abundance of it. It helps keep them warm as they exit the womb," says Philipp Scherer, PhD. He's a professor of internal medicine and cell biology at UT Southwestern Medical Center, Dallas. "But people tend to lose brown fat as they get older." Why? Researchers haven't figured that part out yet, Scherer says.
Brown fat might make up a small amount of an adult's total body fat. But more and more studies are showing that some adults have higher levels of brown fat than expected.
It's sprinkled in between areas of white body fat, usually in the:
- Upper chest
How is it different from white fat?
- Brown fat burns calorie-loaded fats called lipids.
- White fat is a "bad" fat that stores those lipids, creating unhealthy belly fat and thicker thighs.
How do I know if I have brown fat?
There's no easy way to tell. You can't see it by just looking at your body. In the past, researchers have seen it when doing biopsies on babies and rats. But as body imaging methods have advanced, so has the ability to view brown fat.
"When radiologists started doing PET [imaging] scans, they started seeing areas in adults that they couldn't identify as cancer or inflammation," says Anastasia Kralli, PhD. "Those areas turned out to be brown, or beige, fat in adults." Kralli is an associate professor of chemical physiology and cell biology at the Scripps Research Institute in La Jolla, CA.
How can you gain brown fat?
Turn your thermostat down a few degrees, or possibly take a brisk walk in the winter. Evidence shows that as the temperature drops, the amount of calorie-burning brown fat goes up. But experts say there may not be a recommended temperature, and the impact of how long you stay in the cold isn't clear.
A small study earlier this year suggested that long-term exposure to cold may spur brown fat growth, while warmth appeared to suppress it. Researchers followed five men ages 19-23 for 4 months and set the temperature in the rooms where they slept.
Results showed that mild cold – about 66 F – boosted the men’s brown fat amount and calorie-burning activity by 30% to 40%. Mild warmth, meanwhile – about 80 F – lowered their amount of brown fat.
Researchers at UT Southwestern have studied whether cold temps simply turn white fat into brown fat, or if the body can actually make more brown fat cells.
"It is clear, at least in mice, that these are new brown fat cells, not simply cells that are changing," Scherer says.
When you're cold, nerve cells in brown fat release a certain hormone that boosts their calorie-burning ability. This can help with fat loss.
"Brown fat is the good fat -- it helps burn calories and can be used to get rid of excess calories," Kralli says. "But, we still need more understanding of how brown fat is activated. For instance, is it seasonal? Could how we heat our houses be a contributor to obesity?"
Research shows that home temperatures have gotten warmer over the past few decades in the U.S. and the United Kingdom, writes Paul Lee, MD. He's a research fellow at Australia’s Garvan Institute of Medical Research. He says it's tempting to speculate that this temperature shift could play a role -- along with unhealthy diets and not enough exercise -- in the rise in obesity.
In a small 2013 Japanese study, researchers asked 12 young men with lower-than-average amounts of brown fat that burned calories to sit in a 63-degree room for 2 hours a day for 6 weeks. At first, the men burned an average of 108 extra calories in the cold compared with normal indoor temperatures. After 6 weeks, they were burning an extra 289 calories in the cold.
Can brown fat help you lose weight?
Just how many calories you can burn by boosting brown fat is still up for debate.
"The best estimate is that you might burn 300-400 extra calories a day," Scherer says. "Now, that is substantial, but it's not necessarily going to melt the pounds away. However, in combination with lifestyle and diet changes, it could help people get to their target weight faster."
An October 2014 study says increasing the calorie-burning activity of brown fat is "a promising option for innovative weight-lowering therapies." Scientists involved in brown fat research hope their findings will lead to new medications that can trigger the development of these "good" fat cells.
"We're not quite there yet, so the most effective way to [gain brown fat] now is to expose yourself to the cold," Scherer says.
Besides weight loss, what else might brown fat do?
If the findings prove true in people, it could impact the ability to manage diabetes.
"I think we are going to see much more of this [research] in the next few years," Kralli says.