Why Brown Fat Is No Obesity Cure… Yet

Jan 24, 2012 1:52pm

If you were asked to envision a dream solution for the obesity epidemic, you couldn’t do much better than the concept of calorie-burning fat — in other words, “good” fat in the body that essentially burns calories.

So it may come as little surprise that today’s headlines about brown fat are getting a fair bit of attention.

The bad news is that what we know at the moment is not going to help you get any slimmer — at least not in the foreseeable future.

True, brown fat sounds great as a concept. We know that it exists in the bodies of some mammals, and its main function is to produce heat in cold conditions. It’s a key survival mechanism for some animals living in colder environments that allows them to produce body heat without having to deplete precious energy stores, which happens when muscles shiver in the cold.

In order to produce this heat, brown fat burns calories. This differentiates it from the white fat with which all of us are familiar — and which tends to sit in unsightly lumps around our bellies, butts and thighs.

Until recently, brown fat was thought to play a metabolic role only in small mammals and infants; only in recent years has its presence and metabolic role in adult humans garnered serious interest.

So the excitement is understandable. After all, if more of us humans could somehow offset some of our white fat with brown fat, we might not have such a huge problem with obesity.

Unfortunately, it’s not that simple — and the study released today in the Journal of Clinical Investigation may not do much to advance what we know about how brown fat is relevant to humans.

In this study, Canadian researchers exposed healthy men ranging from 23 to 42 years of age, to cold temperatures. Researchers used medical scans to detect evidence of the activity of brown fat in the body. What they found was that the amount of calories the men burned while at rest did increase when they were exposed to cold. The men who were thought to have more brown fat actually shivered less — lending some credence to the idea that their brown fat was kicking in to burn calories.

This finding was tempered by the fact that the study only included six participants and that there was no control group with whom to compare the men who were exposed to the chilly temperatures. Additionally, the study was not designed to see the brown fat directly, only to measure its activity indirectly. So if you’re looking for proof of the existence of brown fat in humans, you might need to wait a little longer.

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

Katz admits, though, that current findings on brown fat are intriguing. And they paint a different picture of what experts thought about it even just a few years ago.

“Up until now, my inclination has been to say the role of brown fat [in weight loss] is very small,” he said. “If that role is not so modest, then that becomes an important topic. I don’t think we’re quite there yet, but this paper points intriguingly in that direction.”

Still, the current body of research does not offer us any suggestions of how brown fat might be used to prevent or treat obesity. Would people engage in some not-yet-developed form of reverse liposuction that would somehow pump brown fat in? Would we take a pill? Crank up the air conditioning to create arctic conditions in our homes? Don’t laugh; Katz said the body actually does burn calories to maintain body heat.

“We already know that people could lose weight by exercising and eating better,” Katz said. “So which is less fun: eating well and being physically active, or being cold all the time? Being cold isn’t a lot of fun.”

And then there are the ways scientists may come up with in the future to “cheat” the system. In one tantalizing study published last July, researchers were able to turn white fat into brown fat by blocking a natural chemical in the body, leading to weight loss, improved blood sugar levels and insulin tolerance. This, of course, was an experiment on mice; scientists said human applications were, in all likelihood, far down the road.

And they may not be without side effects, Katz noted – at least if past experience is any indication.

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

Safe or not, it will likely be years before such options are even available. Until then, the advice remains the same – exercise, control your calories, and avoid the other kind of brown fat… the kind that’s in that extra slice of chocolate cake.

Dr. Patrick Popa with the ABC News Medical Unit contributed to this report.

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