BAT is one of two types of fat, (the other being white fat), which is found in humans and other mammals. In this study we aim to further our understanding of how BAT works in humans. Studies in animals show that in addition to cold exposure, BAT is also activated by ingestion of a meal, and to different amounts depending on the meal composition, and more importantly, total energy content. However we have only a very limited understanding of BAT function in response to meals in humans. Since BAT function is defective in obesity, and its activity and function are impacted by diet, here we will find out whether a single high energy meal composed entirely of lipid (fat) can increase BAT activity. In future these findings and those of subsequent studies may have important implications for the management of obesity and related diseases.