15 Minutes in the Cold Equal to an Hour on a Bike

Stepping out into the cold may not seem like the healthiest idea, but if you're trying to lose weight, going outside and shivering may actually be helpful, according to a small new study published in the journal Cell Metabolism. Researchers from the Garvan Institute of Medical Research in Australia found that not only can shivering help turn energy-storing white fat into energy-burning brown fat, shivering for 15 minutes is equivalent to riding an exercise bike for an hour.

So how does it work? It turns out that not all fat is equal. White fat stores energy in large fat droplets, whereas brown fat keeps energy in small, ready-to-burn droplets. Several studies have shown that higher levels of brown fat are associated with lower body weight, and can offer protection against diabetes, obesity, and other diseases.

"Brown fat is something that all newborns have," said Marie-Pierre St-Onge, MD, a researcher with the New York Obesity Nutrition Research Center at Mount Sinai St. Luke's Hospital in New York City. "It was thought that as you get older, you no longer had any, but several years ago, researchers found that people are still making quite a bit of brown, and that it's induced by cold exposure."

In this most recent study, researchers exposed 10 volunteers to temperatures between 12 and 18 degrees Fahrenheit to induce shivering, and drew blood to measure hormone levels. The researchers found that after shivering for 15 minutes, the participants released irisin and FGF21, hormones released by shivering muscle and brown fat, respectively. And when those same hormones were administered to white fat cells in a laboratory, the white fat started to emit heat - a hallmark of brown fat.

"There's no doubt that cold exposure could lead to benefits by activation of brown fats," said study author Paul Lee, MD, an endocrinologist with the Garvan Institute. "The hormones stimulated can turn ordinary fat into brown fat."

And when the volunteers were put on exercise bikes for an hour, the researchers found that shivering in the cold for 15 minutes was just as effective.

"The release of the hormones was similar during both," Dr. Lee said. "This shows that both moderate exercise and cold exposure could be an effective way to fight obesity."

So could frigid fitness be the kick-start you need to get into shape?

Celebrity nutritionist and fitness expert JJ Virgin said the findings show the benefits of getting out there and exercising - no matter the weather.

"You could increase the benefits of burst training [a type of high-intensity circuit training] by training outdoors in cold weather," Virgin said. "It's not for the timid, but bursting up a park hill, or any other way you do burst training outdoors, during the colder months could create even bigger benefits."

But even Dr. Lee said that you need to take precautions before going out in the cold.

"Cold exposure is like exercise, and it might require training," he said. "I wouldn't recommend someone who never ran before to run a marathon, and I wouldn't recommend someone who has never gone outside to go out and stand in the cold. But you could start by turning down the thermostat at night and building up your cold tolerance."

But others aren't so sure.

"Going out in the cold and shivering is not a practical treatment approach for weight loss," said Christopher Ochner, PhD, obesity expert and assistant professor in the departments of pediatrics and psychiatry at the Icahn School of Medicine at Mount Sinai in New York City. "Elevations in metabolism are almost 100 percent countered by inadvertent and usually unnoticed increases in caloric intake. People will likely just ingest more calories during the day to make up for the extra calories they burnt shivering and, therefore, would get very little practical benefit from it in terms of weight loss."

"Even if it were effective, nobody would do it because it's extremely uncomfortable," Dr. Ochner added.

Dr. Pierre-St. Onge said she's ultimately on the fence.

"The findings suggest that going out into the cold could be good for you," Dr. Pierre-St. Onge said. "Having more brown fat can improve weight regulation and help increase your energy expenditure. It's still unclear if exercising in the cold will do anything, but it's possible that if you go out and don't dress for the weather, it could help with weight loss."