Brown fat mitochondria contain uncoupling proteins that generate heat and reduce free radical production.

“What brown fat has a lot of is mitochondria. And within those mitochondria, they're actually quite different. They have high levels of proteins called UCPs, or uncoupling proteins, which insert into the membrane of the mitochondria and allow those protons that were built up to leak through; instead of going through that pump that makes the energy, they leak through.”