The study of NAFLD has been limited by several factors, including the difficulties associated with studying liver metabolism in vivo in humans. Our group has pioneered new methods that use nuclear magnetic resonance (NMR) to measure intermediary hepatic metabolism in humans with a goal of directly studying the pathophysiology of bland steatosis and NASH. In this study, these noninvasive methods will be used to characterize and compare the metabolic alterations that accompany bland steatosis and NASH and test the hypothesis that detects if hepatic mitochondrial metabolism contribute to both disorders. Such characterization is fundamental to establishing a rational approach to the prevention and treatment of NAFLD and may provide simple, non-invasive methods to differentiate benign and progressive forms of NAFLD.