Obesity is a growing epidemic and is associated with an increased risk of heart attack and stroke. The investigators know that obesity leads to abnormalities in how the blood vessels and the heart function and that these abnormalities are an important cause of this increased risk in obese individuals. While improvements in these abnormalities have been reported with marked weight reduction (eg surgery) and lifestyle changes including exercise training, it is not clear that these abnormalities can be substantially reversed with standard dietary interventions. Additional information is needed regarding the degree of weight loss required, the time course of these improvements, nor the mechanisms. All of these have major implications for the potential role of weight loss in the management of these patients.