Brown Fat: Burning Body Fat Instead of Storing It

How do animals stay warm in the winter?  I don’t know about you, but I personally like the southern migration solution – avoid the problem altogether.  For those animals that don’t (or, like most of us, simply can’t) head south for winter, other common solutions are to grow a thick fur coat and/or add a layer of fat to insulate the body.  Fat can indeed insulate the body, helping to keep it warm, but there are actually two types of fat, and only one of those types is good for insulation.

The cells most people think of when picturing fat cells are storage centers for fats, and they have one big blob of fat that takes up most of the space in the cell.  These are the pesky type of fat cell that most of us wish would disappear from our mid-sections.  Due to their storage of a large droplet of white-colored fat, these cells look white under a microscope, so they are called white fat cells.

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The other type of fat cell has a totally different role in the body, and it is also pretty important for staying warm in winter.  These are brown fat cells, and they burn fat instead of storing it.  That’s right: there are cells in your body that are capable of burning fat without you even needing to get off the couch and go for a run.  Unfortunately, scientists don’t fully understand how these cells are turned on, so don’t give up on your resolution to exercise just yet.

Now you may be wondering why cells that burn fat could help you stay warm in winter, since it seems counter to our belief that extra fat helps keep the body warm.  Brown fat cells actually do one better than mere insulation.  They burn fat to generate heat, thus enabling a body to stay warm even in winter.

I mentioned that white fat cells are white because of the huge fat droplet in the cells; brown fat cells look brown under a microscope.  This is because they have tons of mitochondria, which are brown in color, thus making the whole cell look brown.  Mitochondria are basically the power plants of our cells, churning out a molecule called ATP, which is the battery used to power everything your cell does.  It makes sense that a cell needing lots of energy would have lots of mitochondria, such as a muscle cell.  But why would a cell that generates heat need a lot of “batteries”?

The answer turns out to be unexpected: the cell isn’t using the mitochondria to make ATP.  Usually, mitochondria use the energy gleaned from breaking down fats, sugars, or carbohydrates to build ATP.  In brown fat cells, that energy is dissipated as heat instead.  When your body is cold, the brain activates brown fat cells to start burning heat, and it sends signals to the white fat cells to release some of their stored fat.

Due to their ability to burn fat, brown fat cells have huge promise for combatting obesity.  If researchers can figure out how to activate brown fat cells in a healthy, controllable manner, treatments could be developed to aid people with weight loss.  Also exciting is a series of discoveries about “beige” cells.  It may be possible to convert white fat cells into brown-like cells, thus decreasing the number of fat-storing cells while simultaneously increasing the number of cells that burn fat.

While it may be a few years before brown fat cell weight-loss programs are a reality, there is a silver lining: every time you head out into the polar vortex and lament how cold you are, you can be comforted by the fact that your brown fat cells are burning some fat to help keep you warm.

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