Brown Fat and Weight Loss
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Brown Fat and Weight Loss

It sounds crazy, but it's now well-documented: Subjecting your body to cold temperatures may actually help you drop pounds. Several recent studies show that forcing the body to work hard to stay warm may be a secret ticket to weight loss.

Just a few years ago, scientists discovered that, along with the jiggly white fat that piles up on our midsections, we also have brown fat, which exists primarily to keep us warm. Experts have always known babies have brown fat, but they thought it naturally disappeared over time. It turns out adults have it too, and lean people tend to have more than heavier folks.

Unlike white fat, which stores excess calories, brown fat burns calories. It works like a furnace, pulling sugars from the blood and from white fat stores to generate heat. This process is called non-shivering thermogenesis. Basically, it means that when exposed to chilly temps, well before you feel uncomfortably cold and start to shiver, your body is already hard at work trying to keep you warm. But brown fat can only do so much. When it can no longer beat the chill on its own, your muscles start to contract – or shiver – to churn up heat.

Still, experts have found that non-shivering thermogenesis burns a surprisingly huge amount of energy. It can account for up to 30 percent of the body's energy budget, according to a new paper published in Trends in Endocrinology & Metabolism. This means that lower temperatures can significantly affect the amount of energy a person expends overall, according to the paper's authors, a team of researchers from the Netherlands who've been studying brown fat for a decade.

In fact, these scientists say that sitting around in our cozy-warm homes and offices all day and not forcing our brown fat to generate heat may partially explain why so many Americans are overweight. We spend about 90 percent of our time indoors in ambient temperatures, they write, and if we just turned down the thermostat, we could shed some flab. They reference a Japanese study that found a decrease in overall body fat in people who spent two hours a day in 63 degrees for six weeks.

The Netherlands team also claims that people get used to colder temps after regular exposure, which means their brown fat is being put to work and, as a result, is converting white fat into more brown fat. In one of their studies, they found that after spending six hours a day in 59 degrees for 10 days, people shivered less and their brown fat stores increased. But this is the part that has left experts puzzled. They understand non-shivering thermogenesis, but once brown fat has done all it can to warm you up and your body starts shivering, how and why do brown fat stores keep increasing?

Another new study has finally answered this question. "Shivering stimulates the release of irisin, a hormone that can transform ordinary white fat into healthy brown fat," says Dr. Paul Lee, an endocrinologist at the Garvan Institute of Medical Research in Sydney. "In the laboratory, we found that stimulating human white fat cells with this hormone transforms them into brown fat cells. So, in theory, humans can indeed transform white fat into brown fat."

Exercise also prompts the muscles to release irisin, helping to turn even more white fat to brown. This seems odd since exercise generates heat, not cold, but Lee thinks working out mimics shivering, so it essentially tricks the body into converting white fat to brown. This may be another reason why thinner people, who also tend to exercise more, have more brown fat than heavy men and women. "Brown fat is more abundant in leaner people," says Lee.

Lee's research shows that shivering produces just as much irisin as exercise. In fact, he found that just 10 to 15 minutes of shivering resulted in equivalent rises in irisin as one hour of moderate exercise. That means cold exposure may be just as effective as hitting the treadmill in converting white fat to brown. But can that translate to actual weight loss? "Whether cold exposure can lead to long-term weight loss through brown fat activation requires further study," says Lee.