Obesity has received considerable attention as a major health hazard because of the increase in the prevalence of obesity not only in the United States but also in several other countries worldwide. Obesity is caused by an interaction of environmental factors, genetic predisposition, and human behavior, and is associated with an increased risk of numerous chronic diseases, from diabetes and cancers to many digestive diseases. The obesity epidemic exerts a heavy toll on the economy with its massive health care costs. This article describes some of the epidemiologic features of obesity, including global prevalence, secular trends, risk factors, and burden of illness related to obesity with special emphasis on obesity trends in the United States.
Obesity has received considerable attention as a major health hazard. This article describes some of the epidemiologic features of obesity, including global prevalence, secular trends, risk factors, and burden of illness related to obesity. Special emphasis is placed on obesity trends in the United States.
Definitions for overweight and obesity
The techniques that measure body composition include densitometry, single-cut imaging of the abdomen using computed tomography (CT) scan or magnetic resonance imaging (MRI), and dual-energy X-ray absorptiometry, but these methods are used mostly for research purposes. Body mass index (BMI), which is calculated as the weight in kilograms divided by the height in meters squared (kg/m 2 ), is the most widely used measure of obesity because of its low cost and simplicity. The World Health Organization (WHO) and the National Institutes of Health define a person to be overweight when he or she has a BMI between 25.0 and 29.9 kg/m 2 ; and a person to be obese when he or she has a BMI greater than 30.0 kg/m 2 . In the United States, the criteria for categorizing children as overweight are based on the 2000 US Centers for Disease Control and Prevention’s (CDC) BMI-for-age growth charts. According to these charts a person is considered to be overweight when he or she has a BMI at or above the age-specific 95% BMI percentile. At risk for overweight is a condition when the BMI falls between the 85th and 95th percentiles of the BMI-for-age growth charts.
However, increasing evidence suggests that abdominal obesity, rather than total body fat, is also a useful, independent predictor of several cardiovascular-related outcomes and cancer-related outcomes. Some of the commonly used measures of abdominal obesity are waist circumference, hip circumference, and waist-to-hip ratio.
Obesity trends in adults and children
Obesity Trends in Adults in the United States
A few important sources of epidemiologic data on obesity in the United States are discussed in this article.
The Behavioral Risk Factor Surveillance System (BRFSS) is a state-based cross-sectional random telephone survey of the population of United States of age greater than or equal to 18 years. At the time of the survey, BMI was calculated from self-reported weight and height. The 2008 BRFSS data showed considerable differences in the prevalence of obesity across states. Five states (Alabama, Mississippi, Oklahoma, Tennessee, and West Virginia) had a prevalence of obesity equal to or greater than 30%, and 32 states had a prevalence of obesity equal to or greater than 25%. For comparison, in 1990, no state had a prevalence of obesity greater than 15%; 10 states had a prevalence of obesity less than 10%, and the rest had an obesity prevalence of 10% to 15%.
The National Health and Nutrition Examination Survey (NHANES) is another cross-sectional, nationally representative series of surveys conducted by the National Center for Health Statistics of the US CDC. All surveys included a standardized physical examination, with the measurement of weight and height using standardized protocols that were conducted in a mobile examination center. According to NHANES data for the 2003 to 2004 period, 66.2% of the adults in the United States who were between the age of 20 and 74 years were either overweight or obese, 33.4% were overweight, and 32.9% were obese. Recent data from NHANES show no significant changes in the prevalence of obesity for either men or women between 2003 to 2004 and 2005 to 2006 ( Figs. 1 and 2 ). This possible stabilization in the obesity trends may be an early sign of a plateau in the obesity epidemic. The prevalence of obesity was relatively low and stable between 1960 and 1980, but more than doubled from 15% in 1980 to 34% in 2006.
Data from NHANES show large ethnic differences in the prevalence of obesity, but do not include an adequate number of minorities other than African Americans and Mexican Americans. Based on the data from NHANES for the period 2003 to 2004, African Americans had the highest prevalence of obesity at 45% for men and women between the age of 20 and 74 years; the obesity prevalence was 30.6% for Caucasians and 36.8% for Mexican Americans. The data from NHANES for the period 2005 to 2006 show large differences in obesity prevalence among women belonging to different ethnic groups and between the age of 40 and 59 years, but no significant differences among men belonging to the same ethnic groups. Approximately 53% of African-American women and 51% of Mexican-American women were obese, compared with 39% of Caucasian women.
Overweight Trends in Children in the United States
National estimates of overweight or obesity in children based on the NHANES data show that during the period 2003 to 2006, 31.9% of children aged 2 to 19 years had a BMI at or above the 85th percentile of the 2000 CDC BMI-for-age growth charts, and 16.3% had a BMI at or above the 95th percentile of that chart. Recent data from NHANES show no significant changes in the prevalence of obesity for children aged 2 to 19 years between 2003 to 2004 and 2005 to 2006. The overweight prevalence changed dramatically between 1980 and 2006 for children aged 2 to 19 years, increasing from 5.5% in 1980 to 16.3% in 2006.
Global Trends of Obesity
The current epidemic of obesity has been reported in several but not all regions globally. The highest rate of obesity has been reported in the Pacific Islands and the lowest rates have been seen in Asia. The rates in Europe and North America are generally high, whereas the rates in Africa and Middle Eastern countries are variable. The prevalence of obesity around the world is monitored by the WHO through the Global Database on BMI. The survey data included in the database are identified from the literature or from a wide network of collaborators. However, high-quality data from systematic nationally representative samples is sparse. As of November 2004, the database has compiled data covering approximately 86% of the adult population worldwide. The WHO estimates showed that in 2005, approximately 1.6 billion people worldwide were overweight and that at least 400 million adults were obese. The WHO further projects that by 2015, approximately 2.3 billion adults will be overweight and that at least 700 million will be obese. According to the data from the Global Database on BMI, there are wide variations in the prevalence of obesity throughout the world, ranging from India, where 1% or less of the population is obese, to the Pacific Islands, where the prevalence of obesity can reach up to 80% in some regions.
The change in adult obesity prevalence over time was calculated for 28 countries that have 2 or more nationally representative surveys recorded in the Global Database on BMI. Overall, most countries were found to have rising trends of obesity. Only 2 (Denmark and Saudi Arabia) of the 28 countries showed a falling trend in the prevalence of obesity in men, and 5 (Denmark, Ireland, Saudi Arabia, Finland, and Spain) of the 28 countries showed a falling trend in the prevalence of obesity in women.
Obesity trends in adults and children
Obesity Trends in Adults in the United States
A few important sources of epidemiologic data on obesity in the United States are discussed in this article.
The Behavioral Risk Factor Surveillance System (BRFSS) is a state-based cross-sectional random telephone survey of the population of United States of age greater than or equal to 18 years. At the time of the survey, BMI was calculated from self-reported weight and height. The 2008 BRFSS data showed considerable differences in the prevalence of obesity across states. Five states (Alabama, Mississippi, Oklahoma, Tennessee, and West Virginia) had a prevalence of obesity equal to or greater than 30%, and 32 states had a prevalence of obesity equal to or greater than 25%. For comparison, in 1990, no state had a prevalence of obesity greater than 15%; 10 states had a prevalence of obesity less than 10%, and the rest had an obesity prevalence of 10% to 15%.
The National Health and Nutrition Examination Survey (NHANES) is another cross-sectional, nationally representative series of surveys conducted by the National Center for Health Statistics of the US CDC. All surveys included a standardized physical examination, with the measurement of weight and height using standardized protocols that were conducted in a mobile examination center. According to NHANES data for the 2003 to 2004 period, 66.2% of the adults in the United States who were between the age of 20 and 74 years were either overweight or obese, 33.4% were overweight, and 32.9% were obese. Recent data from NHANES show no significant changes in the prevalence of obesity for either men or women between 2003 to 2004 and 2005 to 2006 ( Figs. 1 and 2 ). This possible stabilization in the obesity trends may be an early sign of a plateau in the obesity epidemic. The prevalence of obesity was relatively low and stable between 1960 and 1980, but more than doubled from 15% in 1980 to 34% in 2006.
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