The main objective of this study is to observe the effects of anti-HIV medication lacking thymidine on mitochondrial metabolism and adipocyte apoptosis (fat cell death). Changes in mitochondrial metabolism and increases in adipocyte apoptosis are associated with lipoatrophy. Lipoatrophy is a common condition characterized by loss of subcutaneous fat and can be caused by many anti-HIV medications. This study will examine the metabolic consequences of the use of thymidine analogue-sparing treatment regimens.