An adaptation to a cold environment is a tendency to generate heat within our body. Some of this heat comes from our fat tissue. Although most fat tissue is "white fat", there are pockets deep within the body that are called "brown fat", which are specially adapted to burning fat and making heat. The investigator believes that our white fat, just underneath the surface of our skin, also has this property to burn fat and make heat, although not at the high level of brown fat. This study is to examine this fat-burning property of the white fat under the skin in response to seasons and to cold. Many such studies have been done in mice, but little has been done in humans.