This chapter looks at several aspects of metabolic and digestive diseases associated with obesity. Obesity is associated with a dual problem for these metabolic processes: excessive delivery of fat and carbohydrate to the liver and reduced effectiveness of insulin in regulating fat metabolism. It is now believed that type 2 diabetes (T2D) is a disease characterized by hepatic steatosis as well as dysregulation of glucose metabolism. Non-alcoholic steatohepatitis (NASH) is an inflammatory disease that results from hepatic steatosis. Insulin resistance is commonly associated with, but not unique to, obesity. The distribution of body fat has significant impact on the development of metabolic disease. Obesity is not an essential component of metabolic syndrome (MetS); however, there is a strong correlation between visceral fat deposits and MetS. Although there are no data implicating stress hyperglycemia and adverse outcomes in bariatric surgery, substantial data exists in other clinical and laboratory conditions.