Effect of Dietary Macronutrient Composition

Obesity is a major factor driving the increased prevalence of hepatic steatosis in the US. However, little is known regarding the relationship between dietary intake and hepatic fat deposition or about the factors that promote loss of hepatic steatosis. Here, the investigators will determine how differences in dietary composition affect the development and regression of fatty liver. The investigators hypothesize that Hispanic subjects with metabolic syndrome will have higher liver fat synthesis rates compared to African American subjects. Using detailed in vivo, serial measurements of fuel metabolism (GC/MS and NMR) fatty acid metabolism will be measured in the liver and periphery. This will be the first study in which these two methodologies are used together to assess both glucose and fatty acid metabolism in the same subjects. Subjects will be tested before and after a dietary weight-loss intervention producing 6% body weight loss over 5 months. The specific aims are as follows: AIM 1: Determine the contribution of peripheral and dietary fat to liver-TG in Hispanics and African Americans with metabolic syndrome. Hypothesis: De novo lipogenesis will contribute to liver-TG in greater quantities compared to African Americans. AIM 2: Determine the effects of low-CHO and low-fat diets on liver fat regression. Hypothesis: Compared to a low-fat diet, a low-CHO diet will markedly decrease markers of inflammation coincident with greater improvements in insulin sensitivity as assessed by an intravenous glucose tolerance test.