Most people assume that all body fat is made the same. We should have some of it, but not too much, and, as we enter adulthood, it basically just sits there storing energy (and building up in areas that we don’t want it to). But that’s only part of fat’s story. We actually have two completely different types of fat cells: Brown fat and white fat. And brown fat, as it turns out, has one incredibly cool—and useful—function. It can burn calories for you.
Scientists have known about these fat varieties for quite some time, but a discovery in 2009 changed our view of their function. Brown fat cells, unlike white, generate heat to keep us warm. That’s particularly useful if you are a baby and you can’t shiver to keep yourself from getting too cold. For that reason, scientists long assumed that only babies possessed those cells. But a series of 2009 studies published at the same time in the New England Journal of Medicine showed that adults have some as well.
Excerpted from Popular Science