Availability of blood samples and biopsies of omental and subcutaneous fat from each of the paired bariatric procedures in this protocol will provide a unique opportunity to study key issues in human obesity. This study tests the broad hypothesis that there are significant and as yet unrecognized differences between the pathobiology of obesity in man and rodents, the identification of which may lead to new therapeutic targets. Accordingly, to facilitate comparisons with aspects of obesity we have already investigated in animal models, we will 1. seek fat depot specific differences in Long Chain Fatty Acid (LCFA) disposition, macrophage infiltration and adipokine production in obesity and after surgery-induced weight loss in man, and correlate them with the presence/severity of the metabolic syndrome (MetSyn); and 2., quantify the relative significance and response to weight loss of different mechanisms contributing to hepatic steatosis and the elevated triglycerides (TG) and reduced High-Density Lipoprotein (HDL) typical of obesity and MetSyn.