Obesity can be simply defined as an excessive amount of body fat which increases the risk of medical illness and premature death. For clinical purposes, assessments that are routinely used to define obesity include body weight and body mass index (BMI)1. The BMI assessment represents the relationship between weight and height, and is derived by calculating either the weight (in kg) divided by the height (in meters squared), or the weight (in pounds) multiplied by 704 divided by the height in inches squared1. Using the BMI as the main criteria, classification of obesity into risk categories have been proposed (Table 3.1). The BMI classification is based on data that has been collected from large epidemiological studies that evaluated body weight and mortality2-4. This classification provides clinicians with a mechanism for identifying patients at high risk for complications associated with obesity. It has been well established that those individuals considered obese, i.e. BMI ≥ 30, are at much higher risk for cardiovascular mortality than those considered overweight, i.e. BMI between 25 and 29.91

(Figure 3.1). The prevalence of obesity has reached epidemic

proportions around the world and the rate continues to increase. According to the World Health Organization (WHO), it has been estimated that over 1 billion adults worldwide are overweight and at least 300 million are considered obese5. Many factors contribute to this rise, but among the major factors are sedentary lifestyles, consumption of high-fat caloric-dense diets, and increased urbanization. In the US alone, data from the National Health and Nutrition Examination Surveys obtained since l960 have suggested that over

64% of the US adult population is classified as either overweight or obese (BMI > 25)5. Whereas the prevalence of overweight adults has increased slightly, from approximately 30.5% to 34.0%, the prevalence of obesity (BMI ≥ 30) has more than doubled from approximately 13% in 1960 to over 30% in the year 20005. Furthermore, the prevalence of individuals with extreme obesity as defined by a BMI ≥ 40 has increased over 6-fold in the same 40-year period (0.8% vs. 4.7%)5. Most of the increase in body weight has occurred since 1980 and, unfortunately, this trend is not expected to change (Figure 3.26).Thus, we will have to address the economic, medical, and psychosocial consequences of this epidemic for years to come.