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New research on ‘brown fat’ is interesting, but beware of the hype

Brown fat may help burn calories, but exercise is still important.

The New York Times ran an interesting article Tuesday that summarizes what scientists are learning about the small amounts of “brown fat” that scientists have recently recognized exist in the adult human body.

As Times reporter Gina Kolata points out, the heat-generating brown fat “burns calories like a furnace.” Until a few years ago, researchers believed this type of adipose tissue was found only in rodents and human infants, both of which are unable to shiver and, thus, need the brown fat to keep warm.

But, then, the stuff was discovered in human adults, albeit in small amounts. One form was found in small deposits under the collarbone and in the neck, spine and upper back, while a second form was found co-mingling with white fat elsewhere on the body.

Studies showed that the brown fat, at least that in the upper body, was absorbing glucose, but did that mean it was actually burning calories? A study published Tuesday in the Journal of Clinical Investigation suggests the answer may be “yes.”

The cold details
In the study, a team of Canadian researchers exposed six healthy men (23 to 42 years old) to cold temperatures, but not to the point of shivering. (Shivering itself burns calories.) Using a technique that involved a radioactive chemical and a special type of scanning device, the researchers watched what the brown fat did as the men’s bodies chilled.

The study found that the men’s metabolic rates — the amount of calories they burned — increased by about 80 percent. The brown fat burned, on average, about 250 extra calories during a three-hour period. Furthermore, the more brown fat a man had, the longer it took for him to begin to shiver.

Intriguing? Yes. Definitive? No. The study was very small and had no controls. And, as ABC reporter Dan Childs points out, the study measured the brown fat’s metabolic activity only indirectly.

“So if you’re looking for proof of the existence of brown fat in humans, you might need to wait a little longer,” he writes.

“The ultimate question is, ‘how big a factor is this when it comes to weight?’ ” Dr. David Katz, founding director of Yale University’s Prevention Research Center in New Haven, Conn., told Childs. “As best I can tell, we can’t answer that questions yet; we’re looking at studies that are very small.”

Other research — but only involving mice — has found that exercise appears to convert white fat into brown fat, which then burns extra calories. If something similar happens in humans (and that’s a big “if” at this point), it may explain, one researcher told Kolata, “why calories burned during exercise exceed the number actually used to do the work of exercising.”

A magic weight-loss pill?
All these findings have naturally ignited the interest of pharmaceutical companies, who, of course, wonder if a drug might be devised that could stimulate the human body to produce more brown fat and thus burn more calories.

But such applications are a long, long way off — and may, in the end, prove neither safe nor effective.

“The history of better weight management through pharmacology is obviously littered with unintended consequences,” Katz told Childs. “As we explore esoteric means of weight loss, we run into one debacle after another.”

One of the authors of Tuesday’s study is slightly less pessimistic. “There is still a lot of research to do before this strategy can be exploited clinically and safely,” Dr. André Carpentier told the Times’ Kolata.

In the meantime, we’d all do well to follow Childs’ advice: “Exercise, control your calories, and avoid the other kind of brown fat … the kind that’s in that extra slice of chocolate cake.”

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