The Epidemiology of Obesity
Section snippets
Definitions and Measurement of Overweight and Obesity
The human body contains essential lipids and also nonessential lipids in the form of triglycerides (triacylglycerols) stored in adipose tissue cells known as adipocytes. Obesity generally is defined as excess body fat. The definition of excess, however, is not clear-cut. Adiposity is a continuous trait not marked by a clear division into normal and abnormal. Moreover, it is difficult to measure body fat directly. Consequently, obesity often is defined as excess body weight rather than as excess
Prevalence and Trends
Prevalence estimates of obesity usually are derived from surveys or population studies because systematic data on obesity generally cannot be gathered from medical records or vital statistics. Virtually all data on prevalence and trends are based on measurements of weight and height using the classifications described earlier rather than on body fat because of the logistical difficulties involved in measuring body fat in population studies.
The NHANES program provides national estimates of
Morbidity in Children
Higher BMI among children is associated with higher levels of blood pressure and serum lipids,65 factors that in adults are associated with higher cardiovascular risk. The implications of a given level of BMI for a child’s future health, however, are unclear. In 2005, the Childhood Obesity Task Force of the US Preventive Services Task Force,66 put the issue succinctly: “We do not know the best way to identify children who are at risk for future adverse health outcomes due to obesity or
Mortality
Obesity has been shown repeatedly to be associated with a modestly increased risk of increased mortality. The magnitude of the association and the exact shape of the BMI-mortality relation, however, has been the subject of much discussion and controversy. A number of studies have suggested that there is a U- or J-shaped curve relating BMI to mortality, with the nadir of the curve around a BMI of 25 or even higher.113, 114, 115
Several studies have suggested that life expectancy is decreased
Determinants of Obesity
The human body can metabolize protein, carbohydrate, and fat to meet energy needs. The principal energy storage is in the form of fat, which, unlike protein or carbohydrate, can be stored in the body in relatively large amounts. This ability to store fat allows energy stores to be mobilized in times of famine or food deprivation. From a historical and evolutionary perspective, starvation is a greater danger than overabundance. Famine and starvation still occur in the world today, especially in
Preventive Efforts
Public health and clinical guidelines on treatment for obesity generally consider degree of overweight, health risk factors, and comorbid conditions in identifying the most appropriate treatment for an individual.5 Evidence suggests that even without reaching ideal weight, a moderate amount of weight loss can be beneficial in terms of reducing levels of some risk factors, such as blood pressure. Many studies of dietary and behavioral treatments, however, show that maintenance of weight loss is
Public Health Impact and Epidemiologic Issues
The net effect of overweight and obesity on morbidity and mortality is difficult to quantify. Higher body weight is associated with an increased incidence and prevalence of numerous conditions, including hypertension, diabetes mellitus, dyslipidemia, certain cancers, musculoskeletal disorders, and CVD, and with increased risk of disability.5 Higher body weights are associated with increased risks of cardiovascular mortality and morbidity.153 On the other hand, higher body weight also is
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The findings and conclusions in this report are those of the authors and not necessarily those of the Centers for Disease Control and Prevention or the National Institutes of Health.