Gastroenterology

Gastroenterology

Volume 132, Issue 6, May 2007, Pages 2087-2102
Gastroenterology

The Epidemiology of Obesity

https://doi.org/10.1053/j.gastro.2007.03.052Get rights and content

In the United States, obesity among adults and overweight among children and adolescents have increased markedly since 1980. Among adults, obesity is defined as a body mass index of 30 or greater. Among children and adolescents, overweight is defined as a body mass index for age at or above the 95th percentile of a specified reference population. In 2003–2004, 32.9% of adults 20–74 years old were obese and more than 17% of teenagers (age, 12–19 y) were overweight. Obesity varies by age and sex, and by race-ethnic group among adult women. A higher body weight is associated with an increased incidence of a number of conditions, including diabetes mellitus, cardiovascular disease, and nonalcoholic fatty liver disease, and with an increased risk of disability. Obesity is associated with a modestly increased risk of all-cause mortality. However, the net effect of overweight and obesity on morbidity and mortality is difficult to quantify. It is likely that a gene-environment interaction, in which genetically susceptible individuals respond to an environment with increased availability of palatable energy-dense foods and reduced opportunities for energy expenditure, contributes to the current high prevalence of obesity. Evidence suggests that even without reaching an 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, have shown that maintenance of weight loss is difficult. The social and economic costs of obesity and of attempts to prevent or to treat obesity are high.

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.

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