Recent dietary guidelines recommend a low fat, high carbohydrate diet. However, data from a variety of sources indicate that diets containing carbohydrate primarily as simple sugars increase cardiovascular risk. The mechanisms of this increased risk are yet to be fully understood. The parent study of this proposal seeks to understand the metabolic consequences of consuming a diet with a low glycemic load versus a diet with a high glycemic load in overweight women. Our ancillary study will extend the parent project by examining some of the cardiovascular consequences of these diets and the mechanisms of the cardiovascular consequences in subjects who consume these diets. Our goals are first to determine if consuming a high glycemic load diet activates endothelium, platelets and monocytes. Second, we will examine mechanisms by which postprandial triglyceride-rich lipoproteins (TGRL) generated by these diets induce arterial injury. We expect that a high glycemic load diet with the accompanying increase in postprandial TGRL will increase platelet and monocyte activation and increase adherence of these cells to endothelium. Further, we expect that high levels of ongoing TGRL lipolysis will increase endothelial layer permeability. The increase in endothelial layer permeability will enable more and larger postprandial lipoproteins to enter the artery wall and localize on the endothelial cell luminal surface and in the subendothelial space. Contrasting sources of dietary carbohydrate may have distinctive influences on the fate of dietary fat. Eating a high carbohydrate, low glycemic load diet may improve fat metabolism, reduce cardiovascular risk factors, and suppress hunger in overweight women. Ultimately this type of diet may be a good alternative to restricting calories for weight management. We urgently need more information about the cardiovascular consequences of some of the commonly used diets in order to properly advise individuals and the public at-large about the long-term consequences of dieting.