Prevention Conference VII: Obesity, a worldwide epidemic related to heart disease and stroke: Group I: worldwide demographics of obesity.

Current concerns about the increased risk of cardiovascular and other diseases induced by excessive weight gain in children and adults have been highlighted by the Surgeon General’s report on the problem of obesity in the United States.1 This call to action followed a global analysis of the problem of excess weight and how to define and combat it that was undertaken by the World Health Organization (WHO) in 19972 and an analogous National Institutes of Health (NIH) assessment and reclassification of US rates of overweight and obesity in 1998.3 It is generally accepted that body mass index (BMI), or weight in kilograms per square meter of height, is a convenient measure of an approximate height-independent index of both children and adults’ weight for height and provides a crude indication of the body’s fat content. It is becoming clear that different ethnic groups have different proportions of fat-to-lean tissues at equivalent BMIs4,5 and that the magnitude of the multiple comorbidities associated with higher BMIs also may differ among different ethnic groups for reasons that may reflect the impact of environmental–genetic interactions. Nevertheless, current international comparisons use a standard format and classification system. In all societies a spectrum of BMIs exists for children and adults of all ages. Individual positions within the percentile range tend to remain the same as children grow and adults steadily gain weight. As the average weight of children and adults increases, so does the spread of BMIs, with a marked progressive increase in the numbers with very high BMIs (see Figure 1). Thus, the escalation in obesity rates reflects the upward shift in body weights of the whole population in response to environmental changes. Adults with a BMI of 18.5 to 24.9 are categorized as being of normal weight, on the basis of international analyses of the health impact of different BMIs in men and women. In all societies with extensive cohort studies, however, the risk of comorbidities tends to rise beginning at a BMI of 20. Thus, the specifications of overweight (BMI 25) and obesity (BMI 30) are arbitrary. Asian expert groups are concerned about higher risk, so Indian physicians and Japanese authorities have set the clinically relevant cutoff points for greater risk of diabetes and cardiovascular disease at a BMI of 23 for overweight and a BMI of 25 for obesity.6,7 Chinese medical professionals have identified a BMI of 24 as overweight and a BMI of 28 as obese.8 On the basis of the standard WHO adult classification system, it is estimated that in the United States, overweight and obesity combined (BMI 25) affect 60% of the population; 27% of US adults are obese (BMI of 30). 9 This statistic reflects a marked increase since the late 1970s, when the combined prevalence of overweight and obesity was 47% and the prevalence of obesity was 15%. 9 This is a populationwide phenomenon, with relatively similar trends by ethnicity and socioeconomic status.10 Trends in diabetes in the US population reflect trends in obesity.11 The prevalence of obesity is somewhat lower in the western region of the United States as compared with the rest of the country and is lower in urban and particularly suburban areas as compared with rural areas.12 Nearly 30% of the US population is composed of diverse ethnic groups that are broadly categorized as black or African American, Hispanic or Latino (including primarily Mexican Americans, Puerto Ricans, Cuban Americans, and persons from Central America), Asians (including persons with ancestry from or who were born in any part of the Asian continent), Pacific Islanders, American Indians or Alaskan Natives, and Native Hawaiians. This proportion will increase