Obesity has emerged as the most pressing nutritional problem facing the developed world. This trend has occurred over a relatively short period of time; in the United States, it appears to have begun in the last quarter of the 20th century. The epidemic in children followed shortly thereafter. The most recent data (1999–2000) from national surveys in the United States suggest that almost two thirds of the adult population is overweight, and almost one third is obese (Flegal et.al, 2002). In children, current estimates (1999–2000) put the prevalence of overweight at 15%, a threefold increase over the past 30 years (Ogden et.al, 2002, p. 32). Although this epidemic has spared no subgroup of the population and has been documented in individuals of all ages and racial/ethnic and socioeconomic subgroups, the problem is greatest in minority populations and among persons living in poverty. Obesity is a global public health problem, affecting virtually every region of the world with the exception of sub-Saharan Africa. .
The World Health Organization (WHO, 2000) defines obesity as a condition of abnormal or excess accumulation of adipose tissue (body fat) to an extent that an individual's health may be impaired. Because the precise measurement of adipose tissue requires invasive laboratory measures, in the population context, a simpler measure on which to base an obesity definition is required. Although imperfect, the Body Mass Index (BMI), defined as weight in kilograms divided by height in meters squared, has been adopted by consensus in the United States by the National Institutes of Health (NIH, 1998) and the Centers; for Disease Control and Prevention (CDC) and internationally by WHO (2000). .
Consensus definitions of overweight and obesity have been set at 25 (overweight) and 30 (obesity), with severity classes of obesity defined as follows: overweight, 25.