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.

The investigators will assess the effects of dietary induced weight loss in both the short and long term on the function of blood vessels and the heart, and the relationship of any changes with markers of inflammation that are present in obesity.

By understanding the factors that are important in reversing these abnormalities in obesity the investigators will be better to identify and reduce heart attack and stroke in obese individuals in the future.

Inclusion Criteria:

• Obese Caucasian men age 18-65 years, who are non smokers, and consuming 2 or fewer standard alcoholic drinks per day (on average over the past 5 years) will be recruited.
• Obesity, for the purposes of this study, is defined by a BMI > 30 and a waist circumference > 102 cm.
• Caucasian men only are enrolled because the cut-off points for the definition of obesity vary significantly by race.

Exclusion Criteria:

• Men are excluded if they have any previously diagnoses or symptomatic atherosclerotic disease, or are taking any cardiovascular medication.
• Men with known gallstones, history of gout, or any contraindication to MRI are also excluded.