Methods

The NHANES was designed to provide cross-sectional estimates of the prevalence of major diseases, nutritional disorders, and potential risk factors among the US population.³ We aggregated data from 2007–2008, 2009–2010, and 2011–2012 and included only adults who were 25 years or older (n = 15 208), excluding those who were pregnant at the time of examination (n = 125) or provided insufficient data regarding weight and height (n = 827). The NHANES obtained approval from the National Center for Health Statistics Research Ethics Review Board and participants provided written consent.

Weight and height were measured during the physical examination using standard procedures. Patients’ BMIs (calculated as weight in kilograms divided by height in meters squared) were classified according to the following categories: underweight (<18.5), normal weight (18.5–24.9), over-weight (25.0–29.9), obesity class 1 (30.0–34.9), obesity class 2 (35.0–39.9), and obesity class 3 (≥40).²

Data regarding patients’ age, sex, and race/ethnicity were collected. Age was classified as 25 to 54 years or 55 or more years. Self-reported race/ethnicity were categorized as Mexican American, non-Hispanic black, non-Hispanic white, or other.

We stratified the analyses by sex and calculated the weighted proportion estimates in each BMI category by race or ethnic group and age group. All statistical analyses were conducted in Stata, version 12.0 (StataCorp LP), using survey analysis procedures to account for the complex sampling design.

Results

Of the sample population, 39.96% (weighted n = 36325297) of men and 29.74% (weighted n = 28894630) of women were overweight and 35.04%(weighted n=31847198) of men and 36.84%(weighted n = 35792733) of women were obese. The weight status distribution was similar for both sexes across racial groups (Table), except for the proportion of non-Hispanic white women, which was higher in the normal-weight than the overweight category. Compared with 20 years ago, the greatest increase in the proportion of patients in the obesity class 3 category was among non-Hispanic black women.

Discussion

Compared with 1988–1994,² the distribution of the population’s weight status has increased in the past 20 years. The rising trends in overweight and obesity warrant timely attention from health-policy and health care–system decision makers. Clinical practice for the prevention and treatment of chronic conditions has mainly focused on screening high-risk populations. As a result, people in higher-weight categories are more likely to be diagnosed with the chronic diseases associated with excess weight² because of more frequent measurements, compared with people in the normal-weight category. This approach may ignore individuals with normal weight and their weight gain, which puts them at risk.

Population-based strategies helping to reduce modifiable risk factors such as physical environment interventions, enhancing primary care efforts to prevent and treat obesity, and altering societal norms of behavior are required.⁴ In 2012, the Institute of Medicine identified population-based obesity-prevention strategies that target physical activity, healthy diet, and models of healthy social norms and provided recommendations on setting specific implementations of those policy and environmental strategies to combat obesity.⁵ The Institute of Medicine⁶ also summarized specific key metrics to evaluate the progress of obesity-prevention strategies toward sustainable implementation. Delivering these strategies is a priority to counter the burden of obesity on contemporary and future generations.

Acknowledgments

Footnotes

References