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Color controls the fate of your fat

Up until last week, I thought fat was fat, fat was white and that was that – as Dr. Seuss might have phrased it.

But then I spoke with Brian Feldman, MD, PhD, a pediatric endocrinologist here at Stanford, about some new work of his and learned that fat comes in two colors – white and brown – and that the proportion of each can make all the difference when it comes to determining how much fat you cart around.

White fat cells are basically tiny little couch potatoes lolling around inside you, shunning active participation in your metabolism, while brown fat cells are torrid little burners of energy. So what causes one fat cell to be white and slothful and another brown and busy?

Feldman and his colleague, research scientist Peter Malloy, PhD, have discovered a protein that acts as a toggle switch, determining which fate a fat cell meets. Called the Vitamin D receptor, the protein binds with Vitamin D (which is actually a hormone, not a vitamin, but old misnomers die hard) and together they are thought to see that adequate calcium levels are maintained in the body, among other jobs.

But the researchers found that the receptor is also critical to determining whether a fat cell ends up white or brown. It all depends on whether the receptor binds to a certain segment of DNA, the details of which you can read about in our press release. If it binds, the fat cell will be white. Says Feldman:

When we first made this discovery, we were curious about whether the amount of vitamin D that people were taking might be decreasing how much brown fat they had. But so far our data show that this activity of the receptor is independent of vitamin D, so people’s ingestion or reserves of vitamin D are unlikely to be affecting this process.

Feldman and Malloy don’t know yet whether the receptor causes white fat cells to turn brown or if they influence things earlier in the process of cellular differentiation by affecting one of the precursor cells along the road to finally becoming a fat cell.

The researchers are now working on developing a therapy to somehow block the Vitamin D receptor from latching onto the pivotal piece of DNA, the result of which would be to turn a fat cell brown. If they can do it, it could be a powerful new weapon in the battle against obesity and the ailments that accompany it. But they caution that even with success, any such therapy would be years away from reaching the general public.

Louis Bergeron is a San Francisco-based science writer covering pediatrics for the medical school's Office of Communication and Public Affairs.

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