Can fat-melting 'hot pants' help you lose weight?

How's this for a hot fitness trend: Fat melting tights that help you burn off 11 percent more calories while you exercise and 13 percent more calories even after you stop. Sound too good to be true? Maybe.

Dessi Bell, a 28-year-old investment banker told ABC News she invented the tights, called Zaggora HotPants, to drop a few pounds for her wedding.


They're so effective at melting off fat, she says, because they make you sweat and sweatburns excess calories. As proof, she cited a study performed by the Chelsea School at Brighton University in England, but the study has yet to be published in a peer-reviewed journal, the company says.

And Dr. Aaron Cypess, an obesity researcher at Harvard's Joslin Diabetes Center in Boston, was skeptical. According to Cypess, science has shown for decades that turning down the thermostat—not up—is the better way to burn extra calories.

"It's not clear to me from a physiological perspective why heating someone up would cause them to burn more calories because the body does not burn many more calories when you get hotter," says Cypess. "When you're colder your body needs to generate more heat to keep you warm. That takes energy in the form of calories."

As Cypess explains it, cool temperatures seems to spur the calorie-burning capability of muscle tissue, and of a special, metabolically active type of body tissue known as brown fat. Adults have small amounts of brown fat, mainly concentrated in the abdomen and neck.

Studies have shown that if you cool a room down to the mid-sixties and lounge around all day in a tee-shirt and shorts, you can burn an impressive 100-300 extra calories per day.

But don't rush to work out in an ice-cold room or get apparel like Cool Shapes just yet. (These are the fitness-fad opposite of HotPants; you basically pack ice into your workout pants to spot reduce your body's trouble zones).

Cypess says a lot more research needs to be done on how colder temperature might affect weight loss. Ironically, he says we already know that cooler temperatures are the least likely to benefit obese people because they have greater insulation in the form of fat.

"What we don't know yet is the best way to cool the body down or whether cold will stimulate hunger. In this era of readily available calories, a person might simply eat more to compensate for the extra calories they burn off," Cypess says.

Cypess says HotPants seems to be a new variation of older weight-loss fads, such as the plastic sauna suits people used to wear back in the 1970s. Any weight loss they help you register on the scale, he says, is probably a temporary loss of water weight you'll gain back as soon as you take a drink.

But the company begs to differ.

"Clinical tests on HotPants have shown that they are effective at increasing the user's metabolic rate during exercise in comparison to standard exercise clothing," the company said in an email. "Our customers have reported to us that when using HotPants in conjunction with an active lifestyle and a healthy diet, they have helped them get to their desired figure, and feel and look fantastic!"

Women need to wear them while doing at least 30 minutes of exercise to feel the benefits, they say, "what they ARE designed and proven to do is to help women maximize the results of the exercise they are able to fit into their lives."

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