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‘Brown Fat’ Studies Provide New Medical Insights, Hope For Weight Loss

April 9, 2009 at 6:40 PM EDT
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New studies reveal that "brown fat," a type of fat scientists previously thought disappeared after infancy, can burn large amounts of calories if activated by cold temperatures. An author of one study explains the discovery and its possible medical applications.

JUDY WOODRUFF: Well, it may sound like an oxymoron, but our next story is about what you might call “good fat.” The fat in question is actually called “brown fat.” Its color comes from energy-burning cells containing iron. More importantly, though, those cells burn off calories.

For years, scientists knew babies had this kind of fat tissue, but thought it largely disappeared as infants grew older. Well, now a trio of studies published in the New England Journal of Medicine shows that brown fat is found — I think I need to take a break, and we’ll be right back.

JUDY WOODRUFF: I’m sorry about that. But the fat in question, as we said, is actually called “brown fat.” Its color comes from energy-burning cells containing iron. But the most important thing is those cells burn off calories.

Now, for years, scientists knew babies had this kind of fat tissue, but they thought it disappeared as infants grew older. But now a trio of studies published in the New England Journal of Medicine shows that brown fat is found among adults, as well.

There’s a lot of attention around the findings. And to help explain it, we turn to an author connected with one of the studies. He is Dr. Ronald Kahn. He’s with the Joslin Diabetes Center in Boston.

Dr. Kahn, thank you very much for being with us.

First of all, tell us, again, what is brown fat? It doesn’t really sound like fat if it’s doing good things.

DR. RONALD KAHN, Joslin Diabetes Center: Well, thank you, Judy. The issue is that the body is mostly filled with white fat. That’s the kind of fat that’s under our skins or inside our bellies or around our various organs. And that’s most of the fat we have.

But there is a small amount, probably just an ounce or two, of this brown fat. And it does, as you say, look actually brown because of these energy-burning mitochondria that’s a part of the cell that burns the energy. And that’s the part of fat that we were looking for in these studies.

Brown fat controls metabolism

JUDY WOODRUFF: And why were you just now able to identify it? As we said, for the longest time scientists thought it largely disappeared in adults.

DR. RONALD KAHN: Right. Well, we thought it might be there for two or three reasons. The first is that there are actually now more and more studies in animals, particularly in mice, showing that brown fat may be an important controller of metabolism.

For example, some mice that tend to gain weight versus others that tend not to gain so much weight on high-fat diet have less brown fat than the mice who are protected from the weight gain. And we thought that probably humans had it, but maybe we were looking in the wrong place.

JUDY WOODRUFF: Now, what's the significance of this? And why are scientists excited about this discovery?

DR. RONALD KAHN: The major reason that we're excited is not only that there is brown fat, but these studies -- at least two of the studies that you mentioned -- ours and one other -- show that this seems to correlate best with being lean so that younger, leaner people have more brown fat, older, heavier people have less brown fat.

And this would suggest that maybe having brown fat is one of the things that protects us from becoming obese, particularly maybe as we age. It also suggests that maybe this might be a new approach to both prevention and even treatment of obesity.

JUDY WOODRUFF: And so how would that work? Scientists are already thinking ahead to what might they be able to do.

DR. RONALD KAHN: Well, there are two possibilities. One would be to stimulate the activity of the brown fat, and this might be possible through hormonal treatment. For example, some hormones, like stress hormones, increase the activity of brown fat.

But it also may be possible to actually increase the amount of brown fat. We've been, for example, looking at a growth factor that stimulates brown fat to grow in culture -- that is, in a test tube -- and we're hoping to see if that will also stimulate the brown fat to grow in rodents and eventually maybe even people.

Research will take years

JUDY WOODRUFF: And for people who are listening closely to this -- because just about everybody at one point or another in their life has worried about or thought about their weight -- what are the practical implications? I mean, are we talking years, decades?

DR. RONALD KAHN: Well, I think that the type of research that we're looking at will certainly take years, because, after all, we always have to test any compounds both in cells and in animals before we go to humans. But I think that having this new method to measure the activity and the amount of brown fat will speed up the research, because now we have an end point to look for that we can measure actually in people in real time.

JUDY WOODRUFF: Is it understood, Dr. Kahn, why brown fat is there, what puts it there in the first place, and why it stays in some people and not in others?

DR. RONALD KAHN: Brown fat, at least in babies and rodents, like mice and rats, is there to partly generate heat, to increase the body temperature and keep them warn. And most people felt that maybe as adults had less need to stay warm by this approach, that their muscle and other tissues took over, that they didn't need brown fat.

But we think that actually it's there to help balance the overall energy. White fat stores the energy, and the brown fat burns some. And maybe controlling this balance will allow us to control how fat we are.

Cold stimulates brown fat

JUDY WOODRUFF: And so are -- do I hear you saying it's not understood yet or not known whether somebody could do something themselves to make their brown fat last longer?

DR. RONALD KAHN: Right. Well, we don't know for sure. We do know that people who work outside in cold climates, like Scandinavians working in the forests of Finland and so forth, these people do have more brown fat when people look for it.

And in some of the studies -- in our study and the other studies -- we showed that generally, for example, in the U.S., people have more brown fat in winter months than they do in summer months.

Two of the studies actually put people in the cold to help stimulate the amount of brown fat, or at least its activity.

JUDY WOODRUFF: And just quickly -- and you may have mentioned this a minute ago -- that women are known to have some more of it than men?

DR. RONALD KAHN: In our study, we found that women had brown fat that was detectable about twice as often as men, but in the other studies it didn't seem to be quite so different. And I think that's because in the other studies they were stimulating it, and we were looking just as people kind of walked in off the street.

JUDY WOODRUFF: Well, it's one more piece of scientific information that a lot of people are going to be paying very close attention to.

DR. RONALD KAHN: Thank you.

JUDY WOODRUFF: Dr. Ronald Kahn, thank you very much.

DR. RONALD KAHN: Thank you.