'Brown fat', a wondrous tissue, can burn oodles of flab and help us stay slim and trim. Brown fat is present in most, if not all, adults mainly just behind the collarbone.
http://www.ummid.com/news/2011/September/07.09.2011/tissue_that_burns_oodles_of_flab.htm
http://www.ummid.com/news/2011/September/07.09.2011/tissue_that_burns_oodles_of_flab.htm