The study is designed as a prospective, blinded diet intervention study during which the participants consume either fructose- or HFCS-sweetened beverages (providing 10%, 17.5% or 25% of energy) with meals. In addition, there will be two control groups, with one group consuming 0% sugar beverages sweetened with sucralose and the other consuming glucose-sweetened beverages at 25% of energy requirement. Experimental procedures, including 24-hour serial blood sampling, post-heparin infusions, gluteal biopsies, Magnetic Resonance Imaging of the liver and the abdomen, and Oral Glucose Tolerance and Disposal Tests, are performed during baseline and at the end of a 2-week intervention period at the UC Davis Clinical and Translational Science Center (CTSC) Clinical Research Center (CCRC). During the inpatient periods, subjects are served energy balanced diets. The diets provide 15% of energy as protein, 30% as fat, and 55% as carbohydrate. During baseline testing, the carbohydrate content consists primarily of complex carbohydrate (>97%). During intervention the 55% carbohydrate will consist of 10% sugar/45% complex, 17.5% sugar/37.5% complex, or 25% sugar/30% complex depending on the diet group to which the subject is assigned. During the outpatient intervention periods, the subjects reside at home and are provided with fructose- or HFCS -sweetened beverages that are consumed with each meal along with a self-selected ad libitum (usual) diet.