It has long been thought that adults have only one type of fat: the lumpy white/yellow fat that we always blame for our rolls. White fat stores any extra calorie you eat for your future energy needs, but if you have a lot of it, it’s also associated with health issues like insulin resistance and heart disease. Although, as it turns out, it is not the only type of fat in our body.
Humans also have brown fat located in deposits in the neck and around the clavicles. Although people have an abundance of this in childhood, we have much less in adulthood, and some of us have nothing.
Brown fat does not behave in the same way as white fat. Brown fat gets its color and name from its iron-rich mitochondria, and scientists describe its function more as a muscle than we had ever thought. For example, brown fat is a good insulator because it burns white fat for energy.