Nonalcoholic fatty liver disease (NAFLD) is the most common type of liver disease in the United States. The incidence of NAFLD is very similar to that of obesity, type 2 diabetes, and the metabolic syndrome. The investigators hypothesize that there may be a relationship between over-nutrition, decreased physical activity and the development of fatty liver. The purpose of this study is to identify the types of fats and proteins, and the quantity of each, that are associated with increased severity of NAFLD.