Brown fat: Where it’s at

When it comes to the “good” fat, some people shoulder lots of it — literally.

The body makes two very different forms of fat. The energy-storage depots that weight-loss diets target are comprised of white cells. As they accumulate copious amounts of lipids, they turn unhealthy, spewing pro-inflammatory chemicals that have been linked with an increased risk of heart disease.

The less well known brown fat actually fosters the burning of energy. These dark cells derive their color from the dense concentrations of iron-rich mitochondria — essentially chemical furnaces that help power a cell’s activities, explains Aaron Cypess of the Joslin Diabetes Center and Beth Israel Deaconess Medical Center in Boston. Typically found in babies, brown fat has tended to be fairly elusive in adults. But preferentially encouraging its development over white fat could be a good thing in populations who are tipping the scales at unhealthy weights.

At the Endocrine Society meeting in Washington, D.C., this week, Cypess’ group will report finding that some people develop substantial stores of the somewhat preferable brown fat cells — but not where we’d usually expect to find fat. At least in adults, Cypess reports, brown fat develops predominantly around the neck, across the shoulder blades — and, if there’s enough of it, in a band that can spill down into the chest.

So far, his group has turned up 106 people — 5.4 percent of those screened — hosting “significant amounts” of brown fat. Women were twice as likely as men to fall into this group. Other characteristics of adults with substantial brown fat: being relatively young, lean and not taking beta-blocker drugs to manage high blood pressure.

Hosting 50 grams of metabolically active brown fat can burn 300 to 500 calories a day, Cypess told reporters at a briefing this afternoon. That’s the equivalent of jumping rope for a half hour or swimming for 45 minutes. Obviously, then, increasing stores of brown fat — or the activity of this fat — can help counter obesity, Cypess says.

He didn’t offer any suggestions on how to do that, but several Japanese research teams have been exploring this in animal studies for years. A decade ago, one of these groups showed that feeding animals diets enriched with sulfur-based compounds from garlic (such as alliin and diallyldisulfide) revved up heat production by the rodents’ stores of brown fat. More recently, another group showed that the purple pigments in some foods (in their case, corn) can diminish the amount of energy stored in white fat — with no loss, to speak of, of brown fat.

Hmmm. Sounds like the starting ingredients for a healthful salad dressing.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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