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Article title: NIDDK _ Statistics Related to Overweight and Obesity: NIDDK
To understand the significance of statistics related to overweight and obesity, it is important to know how overweight and obesity are defined and measured. This fact sheet discusses these terms and their measures, and explains why statistics may differ when obtained from diverse sources. It then presents statistics related to overweight and obesity in the United States.
A number of methods are used to determine if an individual is overweight or obese. Some of them are based on mathematical calculations of the relation between height and weight--others are based on measurements of body fat. These methods are described below.
Body Mass Index (BMI) can be used to measure both overweight and obesity in adults. It is the measurement of choice for many obesity researchers and other health professionals. BMI is a direct calculation based on height and weight, and it is not gender-specific. Most health organizations and published information on overweight and its associated risk factors use BMI to measure and define overweight and obesity. BMI does not directly measure percent of body fat, but it provides a more accurate measure of overweight and obesity than relying on weight alone.
BMI is found by dividing a person's weight in kilograms by height in meters squared. The mathematical formula is:
weight (kg)/height squared (m2).
To determine BMI using pounds and inches, multiply your weight in pounds by 704.5,* then divide the result by your height in inches, and divide that result by your height in inches a second time. (Or you can use the BMI calculator at http://www.nhlbisupport.com/bmi/ or check the chart shown below that has calculated BMI for you.)
* The multiplier 704.5 is used by the National Institutes of Health. Other organizations may use a slightly different multiplier; for example, the American Dietetic Association suggests multiplying by 700. The variation in outcome (a few tenths) is insignificant.
|Source: Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, National Institutes of Health, National Heart, Lung, and Blood Institute, June 1998.|
The National Institutes of Health (NIH) identify overweight as a BMI of 25-29.9 kg/m2, and obesity as a BMI of 30 kg/m2 or greater. However, overweight and obesity are not mutually exclusive, since obese persons are also overweight.1 Defining overweight as a BMI of 25 or greater is consistent with the recommendations of the World Health Organization 2 and most other countries.
Calculating BMI is simple, quick, and inexpensive--but it does have limitations. One problem with using BMI as a measurement tool is that very muscular people may fall into the "overweight" category when they are actually healthy and fit. Another problem with using BMI is that people who have lost muscle mass, such as the elderly, may be in the "healthy weight" category--according to their BMI--when they actually have reduced nutritional reserves. BMI, therefore, is useful as a general guideline to monitor trends in the population, but by itself is not diagnostic of an individual patient's health status. Further evaluation of a patient should be performed to determine his or her weight status and associated health risks.
Weight-for-height charts are another measure used to determine if a person is overweight (although they do not measure body fat). These charts, which have been used by doctors and other health care workers for decades, usually give a range of acceptable weights for a person of a given height. Many versions of weight-for-height charts exist, some showing different acceptable weight ranges for men and women. Health care workers often disagree over which is the best chart to use. The 2000 Dietary Guidelines for Americans, published jointly by the U.S. Departments of Agriculture and Health and Human Services, provide the most up-to-date weight-for-height chart. The healthy weight range in this chart corresponds to a BMI between 18.5 and 25.
There are a number of ways to measure body fat. Historically, the standard method is to weigh a person underwater; this procedure is limited to laboratories with specialized equipment.
Other simpler methods for measuring body fat include skinfold thickness measurements and bioelectrical impedance analysis (BIA). Skinfold thicknesses are measures of the subcutaneous (lying just beneath the skin) fat at specific sites of a person's body, such as the triceps (the back of the upper arm). Accurate measurements of skinfold thickness depend on the skill of the examiner and may vary widely when measured by different examiners.
To measure body fat using BIA, a harmless amount of an electrical current is sent through the body. The body's ability to conduct an electrical current reflects the total amount of water in the body. Generally, a higher percent body water indicates a larger amount of muscle and lean tissue. Mathematical equations are used to translate the percent body water measure into an indirect estimate of body fat and lean body mass. A standard method should be used to measure bioelectrical impedance because dehydration, recent exercise, skin and room temperature, and placement of electrodes all can affect test results. To obtain the most precise reading, the person being tested should fast for at least 4 hours and lie down for at least several minutes prior to testing. BIA may not be accurate in severely obese individuals, and it is not useful for tracking short-term changes in body fat brought about by diet or exercise.
In addition to body weight and height measurements, health professionals may also rely on a person's waist measurement to determine the location of excess body fat and the corresponding health risks. Analogous to BMI, health risks increase as waist circumference increases. A woman whose waist measures more than 35 inches and a man whose waist measures more than 40 inches may be at particular risk for developing health problems. Studies indicate that increased abdominal or upper body fat is related to the risk of developing heart disease, diabetes, high blood pressure, gallbladder disease, stroke, and certain cancers, and is associated with overall mortality (likelihood of death). Body fat concentrated in the lower body (around the hips, for example) may be less harmful in terms of mortality and morbidity (likelihood of disease), with the exception of varicose veins and orthopedic problems.3, 4
The definitions or measurement characteristics for overweight and obesity have varied over time, from study to study, and from one part of the world to another. The varied definitions affect the prevalence statistics of studies and make it difficult to compare data from different studies and from different countries. Prevalence refers to the total number of existing cases of a disease or condition in a given population at a designated time. Some overweight- and obesity-related prevalences are presented in total (or crude) numbers, while others are age-adjusted numbers. For age-adjusted rates, statistical procedures are used to remove the effect of age differences in populations that are being compared over different time periods. Total numbers and age-adjusted numbers will yield slightly different values.
Older studies in the United States have used the 1959 or the 1983 Metropolitan Life Insurance tables of desirable weight-for-height as the reference for overweight.5 More recently, many Government agencies and scientific health organizations have estimated overweight using data from a series of cross-sectional surveys called the National Health Examination Surveys (NHES) and the National Health and Nutrition Examination Surveys (NHANES). These surveys were conducted by the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC). Each of these surveys had three cycles: NHES I, II, and III spanned the period from 1960 to 1970, and NHANES I, II, and III were conducted in the 1970's, 1980's, and early 1990's.
Many reports in the literature use a statistically derived definition of overweight from NHANES II (1976-1980). This definition (based on the gender-specific 85th percentile values of BMI for 20-29 year olds) is a BMI greater than or equal to () 27.3 for women and 27.8 for men. Some studies round these numbers to a whole number, which affects the statistical prevalence. Rounding down will always increase the prevalence, and rounding up will decrease the prevalence. For example, 36.4 percent of women are overweight based on a BMI 27.3. When the BMI is rounded up to 28, only 33 percent of women are overweight (a decrease of 3.4 percent).6
In 1995, the World Health Organization recommended a classification for three "grades" of overweight using BMI cutoff points of 25, 30, and 407. The International Obesity Task Force suggested an additional cutoff point of 35 and slightly different terminology.8
Two organizations within NIH--the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)--convened an expert panel whose report, released in June 1998, provided definitions for overweight and obesity in agreement with those used by the World Health Organization. The panel identifies overweight as a BMI 25 to less than (<) 30, and obesity as a BMI 30. (As explained previously, overweight and obesity are not mutually exclusive, since obese persons are also overweight.) These definitions are based on evidence that health risks increase more steeply in individuals with a BMI 25.
As stated earlier, BMI cutoff points are a guide for definitions of overweight and obesity and are useful for comparative purposes across populations and over time; however, the health risks associated with overweight and obesity do not conform to rigid cutoff points. (For example, an overweight individual with a BMI of 29 does not instantly acquire all of the health consequences of obesity after crossing the threshold of BMI 30). Health risks increase gradually as BMI increases.
Regardless of the definitions used for overweight and obesity, studies have shown that the number of overweight individuals in the United States continues to rise for all age groups.
Overweight and obesity are found worldwide, and the prevalence of these conditions in the United States ranks high along with other developed nations. Approximately 280,000 adult deaths in the United States each year are attributable to obesity.9
Below are some frequently asked questions and answers about overweight and obesity statistics. Unless otherwise specified, the figures given represent total (not age-adjusted) numbers. (Age-adjusted numbers based on the 2000 population census will be posted at http://www.health.gov/healthypeople/.)
* The statistics presented here are based on the
following definitions unless otherwise specified: overweight = BMI 25 to < 30; obesity = BMI 30.
Q: How many adults are overweight?
A: More than half of U.S. adults are overweight (BMI 25, which includes those who are obese).5
All adults (20+ years old): 97.1 million (54.9 percent)
Women (20+ years old): 46.9 million (50.7 percent)
Men (20+ years old): 50.2 million (59.4 percent)
Q: How many adults are obese?
A: Nearly one-quarter of U.S. adults are obese (BMI 30).5
All adults (20+ years old): 39.8 million (22.3 percent)
Women (20+ years old): 23 million (25 percent)
Men (20+ years old): 16.8 million (19.5 percent)
Q: How many adults are a healthy weight?
A: Less than half of U.S. adults are a healthy weight (BMI 19 to < 25).5
All adults (20+ years old): 73.2 million (41.4 percent)
Women (20+ years old): 40.3 million (43.6 percent)
Men (20+ years old): 32.9 million (39.0 percent)
Q: How has the prevalence of overweight and obesity in adults changed over the years?
A: The prevalence has steadily increased over the years among nearly all* racial/ethnic groups,5 as shown in the chart below. For example, from 1960 to 1994, the prevalence of overweight (BMI 25 to < 30) increased from 31.6 to 32.6 percent in U.S. adults. The prevalence of obesity (BMI 30) during this same time period increased from 13.4 to 22.3 percent--a relative increase of more than 50 percent--with most of this rise occurring in the past decade. The prevalence of overweight and obesity increases with advancing age until a person reaches his or her sixties, when it starts to decline.5 From 1991 to 1998, obesity increased in every state of the United States, in both genders, and across all races/ethnicities, age groups, educational levels, and smoking statuses.10
* An exception is the prevalence of overweight in white
men in their twenties to forties, which decreased from the early 1970s to
|Figure 1. Prevalence of Overweight (BMI 25-29.9) and Obesity (BMI 30)|
Source: CDC/NCHS, United States, 1960-1994
Note: Although the definitions of overweight and obesity based on
BMI were slightly different in the 1960s than today's definitions,
the data presented here are comparable. The older data were
recomputed to reflect current
Note: Although the definitions of overweight and obesity based on BMI were slightly different in the 1960s than today's definitions, the data presented here are comparable. The older data were recomputed to reflect current definitions.
Q: What is the prevalence of overweight and obesity in minorities?
A: The age-adjusted prevalence of combined overweight and obesity (BMI 25) in racial/ethnic minorities--especially minority women--is generally higher than in whites in the United States.5
Black women (20+ years old): 65.8 percent
Mexican American women (20+ years old): 65.9 percent
White women (20+ years old): 49.2 percent
Black men (20+ years old): 56.5 percent
Mexican American men (20+ years old): 63.9 percent
White men (20+ years old): 61.0 percent
Studies using this definition of overweight and obesity (BMI 25) provide ethnicity-specific data only for these three racial-ethnic groups. Studies using other definitions of overweight and obesity, as described earlier, find a high prevalence of overweight and obesity among Hispanics and Native Americans. The prevalence of overweight and obesity in Asian Americans is lower than in the general population.1
Q: What is the prevalence of overweight and obesity in children and adolescents?
A: While there is no generally accepted definition for obesity as distinct from overweight in children and adolescents, the prevalence of overweight is increasing for children and adolescents in the United States. Approximately 11 percent of children (ages 6-11) and 11 percent of adolescents (ages 12-17) were overweight* in 1988 to 1994--up from approximately 5 percent in the 1960s and 1970s.11
* Overweight is defined by the sex- and age-specific 95th percentile cutoff points of the revised NCHS/CDC growth charts (preliminary data). The revised growth charts incorporate smoothed BMI percentiles and are based on data from NHES II (1963-1965) and III (1966-1970), and NHANES I (1971-1974), II (1976-1980), and III (1988-1994).
Q: What is the prevalence of overweight and obesity in people with diabetes?
A: Among persons who have been diagnosed with type 2 (noninsulin-dependent) diabetes, 67 percent have a BMI 27 and 46 percent have a BMI 30. 12 An estimated 15.6 million adults in the U.S. (8 percent of men and women age 20 or older) have diabetes, with type 2 diabetes accounting for about 90-95 percent of these cases. The relative risk of diabetes increases by approximately 25 percent for each additional unit of BMI over 22.13
Q: What is the prevalence of overweight and obesity in people with hypertension (high blood pressure)?
A: The age-adjusted prevalence of hypertension in overweight U.S. adults (BMI 25 and < 30) is 23.9 percent for men and 23.0 percent for women, compared with 18.2 percent for men and 16.5 percent for women who are not overweight (BMI < 25). The prevalence for obese adults (BMI 30) is 38.4 percent for men and 32.2 percent for women. 14 (Hypertension is defined as mean systolic blood pressure 140 mm Hg, mean diastolic 90 mm Hg, or currently taking antihypertensive medication.)
Q: What is the prevalence of overweight and obesity in people with high blood cholesterol?
A: The age-adjusted prevalence of high blood cholesterol ( 240 mg/dL) in overweight U.S. adults (BMI 25 and < 30) is 19.0 percent for men and 28.0 percent for women, compared with 14.7 percent for men and 15.7 percent for women who are not overweight (BMI < 25). The prevalence for obese adults (BMI 30) is 20.2 percent for men and 24.7 percent for women.14
Q: What is the prevalence of overweight and obesity in people with cancer?
A: While direct prevalence information is not available, studies have found that heavier individuals are at increased risk for some types of cancers including endometrial (cancer of the lining of the uterus), colorectal, gallbladder, and renal cell (kidney) cancer.15 Almost half of the post-menopausal women diagnosed with breast cancer have a BMI 29.16 In one study (the Nurses' Health Study), women gaining more than 20 pounds from age 18 to midlife doubled their risk of breast cancer, compared to women whose weight remained stable.17
Q: What is the mortality rate associated with obesity?
A: Most studies show an increase in mortality rate associated
with obesity (BMI 30). Obese individuals have a 50-100 percent increased
risk of death from all causes, compared with normal-weight individuals
(BMI 20-25). Most of the increased risk is due to cardiovascular
As the prevalence of overweight and obesity has increased in the United States, so have related health care costs--both direct and indirect. Direct health care costs refer to preventive, diagnostic, and treatment services (for example, physician visits, medications, and hospital and nursing home care). Indirect costs are the value of wages lost by people unable to work because of illness or disability, as well as the value of future earnings lost by premature death.
The statistics presented in question-and-answer form below represent the economic cost of overweight and obesity in the United States in 1995. Unless otherwise specified, the statistics given are from Wolf and Colditz,19 who based their data on existing epidemiological studies that defined overweight and obesity as a BMI 29.
Q: What is the cost of overweight and obesity?
A: Total cost: $99.2 billion
Direct cost: $51.6 billion (5.7 percent of the U.S. health expenditure)
Indirect cost: $47.6 billion (comparable to the economic costs of cigarette smoking)
What is the cost of heart disease related to overweight and obesity?
A: Direct cost related to overweight and obesity: $6.99 billion (17 percent of the $40.4 billion total direct cost of heart disease, independent of stroke)
Q: What is the cost of type 2 diabetes related to overweight and obesity?
A: Total cost related to overweight and obesity: $63.14 billion (more than 60 percent of the total cost of type 2 diabetes)
Direct cost: $32.4 billion
Indirect cost: $30.74 billion
Q: What is the cost of osteoarthritis related to overweight and obesity?
A: Total cost related to overweight and obesity: $17.2 billion
Direct cost: $4.3 billion
Indirect cost: $12.9 billion
Q: What is the cost of hypertension (high blood pressure) related to overweight and obesity?
A: Direct cost related to overweight and obesity: $3.23 billion (17 percent of the total cost of hypertension)
Q: What is the cost of cancer related to overweight and obesity?
A: Post-menopausal breast cancer
Total cost related to overweight and obesity: $2.32 billion
Direct cost: $840 million
Indirect cost: $1.48 billion
Total cost related to overweight and obesity: $790 million
Direct cost: $286 million
Indirect cost: $504 million
Total cost related to overweight and obesity: $2.78 billion
Direct cost: $1 billion
Indirect cost: $1.78 billion
Q: What is the cost of lost productivity related to obesity?
A: The cost of lost productivity related to obesity (BMI 30) among Americans ages 17-64 is $3.93 billion. This value considers the following annual numbers (for 1994):
Workdays lost related to obesity: 39.3 million
Physician office visits related to obesity: 62.7 million
Restricted activity days related to obesity: 239.0 million
Bed-days related to obesity: 89.5 million
Q: How much do we spend on weight-loss products and services?
A: Americans spend $33 billion annually on weight-loss products and services.20 (This figure represents consumer dollars spent in the early 1990s on all efforts at weight loss or weight maintenance including low-calorie foods, artificially sweetened products such as diet sodas, and memberships to commercial weight-loss centers.)
Q: How physically active is the U.S. population?
A: Only 22 percent of U.S. adults get the recommended regular physical activity (5 times a week for at least 30 minutes) of any intensity during leisure time. About 15 percent get the recommended amount of vigorous activity (3 times a week for at least 20 minutes). About 25 percent of adults claim they do no physical activity at all in their leisure time.21
About 25 percent of young people (ages 12-21 years) participate in light to moderate activity (e.g., walking, bicycling) nearly every day. About 50 percent regularly engage in vigorous physical activity. Approximately 25 percent report no vigorous physical activity, and 14 percent report no recent vigorous or light to moderate physical activity.21
Lack of physical activity contributes to the high prevalence of overweight and obesity in the United States. In addition to helping to control weight, physical activity decreases the risk of dying from coronary heart disease and reduces the risk of developing diabetes, hypertension, and colon cancer.21
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) is the part of the National Institutes of Health primarily responsible for obesity- and nutrition-related research. NIDDK supports the study of obesity in its own laboratories and clinics and at universities, hospitals, and research centers across the United States. NIDDK-funded research has helped scientists learn more about the role of genes and metabolism in obesity. Other NIDDK-supported studies have examined the relationship between obesity and other medical conditions such as breast cancer. Ongoing NIDDK research efforts include better ways to define and manage obesity and to understand how the body stores and uses fat.
NIDDK also transfers research knowledge about overweight and obesity to health professionals, patients, and the general public through the Weight-control Information Network.
1 Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, National Institutes of Health, National Heart, Lung, and Blood Institute, June 1998.
2 World Health Organization. Obesity: preventing and managing the global epidemic. Report of a WHO Consultation on Obesity, Geneva, 3-5 June, 1997. Geneva: World Health Organization, 1998.
3 Bouchard C, Bray GA, Hubbard VS. Basic and clinical aspects of regional fat distribution. Am J Clin Nutr. 1990;52:946-950.
4 Peiris AN, Sothmann MS, Hoffman RG, et al. Adiposity, fat distribution, and cardiovascular risk. Ann Intern Med. 1989;110:867-872.
5 Flegal KM, Carroll MD, Kuczmarski RJ, Johnson CL. Overweight and obesity in the United States: prevalence and trends, 1960-1994. Int J Obes. 1998;22:39-47.
6 Kuczmarski RJ, Carroll MD, Flegal KM, Troiano RP. Varying body mass index cutoff points to describe overweight prevalence among U.S. adults: NHANES III (1988 to 1994). Obes Res. 1997;5(6):542-548.
7 Physical status: the use and interpretation of anthropometry. Report of a WHO expert committee. 1995. Geneva: World Health Organization, (WHO Technical Report Series, no. 854).
8 International Obesity Task Force. Managing the global epidemic of obesity. Report of the WHO Consultation on Obesity, Geneva, June 5-7, 1997. Geneva: World Health Organization.
9 Allison DB, Fontaine KR, et al. Annual deaths attributable to obesity in the United States. JAMA. 1999;282(16):1530-1538.
10 Mokdad AH, Serdula MK, Dietz WH, et al. The spread of the obesity epidemic in the United States, 1991-1998. JAMA. 1999;282(16):1519-1522.
11 Troiano RP, Flegal KM. Overweight children and adolescents: description, epidemiology, and demographics. Pediatrics. 1998;101(3, suppl):497-504.
12 Personal communication from Maureen I. Harris, NIDDK/NIH, to Susan Z. Yanovski, NIDDK/NIH.
13 Colditz GA, Willett WC, Rotnitzky A, Manson JE. Weight gain as a risk factor for clinical diabetes mellitus in women. Ann Intern Med. 1995;122:481-486.
14 Brown CD, Donato KA, Obarzanek E, et al. Body mass index and prevalence of risk factors for cardiovascular disease. Obes Res. Submitted for publication.
15 Ballard-Barbash R. Energy balance, anthropometry, and cancer. In: Heber D, Blackburn GL, Go, VLW, eds. Nutritional Oncology. Academic Press, 1998: Chapter 12.
16 Ballard-Barbash R, Swanson CA. Body weight: estimation of risk for breast and endometrial cancers. Am J Clin Nutr. 1996;63(suppl):437S-441S.
17 Huang Z, Hankinson SE, Colditz GA, et al. Dual effects of weight and weight gain on breast cancer risk. JAMA. 1997;278:1407-1411.
18 Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults--The Evidence Report. National Institutes of Health. Obes Res. 1998;6(suppl 2):51S-209S.
19 Wolf AM, Colditz GA. Current estimates of the economic cost of obesity in the United States. Obes Res. 1998;6(2):97-106.
20 Colditz GA. Economic costs of obesity. Am J Clin Nutr. 1992;55:503-507s.
21 U.S. Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General. Centers for Disease Control and Prevention, 1996.
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The Weight-control Information Network (WIN) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). NIDDK is part of the National Institutes of Health under the U.S. Department of Health and Human Services. Authorized by Congress (Public Law 103-43), WIN assembles and disseminates information on weight control, obesity, and nutritional disorders to health professionals and the public. WIN responds to requests for information; develops, reviews, and distributes publications; and develops communications strategies to encourage individuals to achieve and maintain a healthy weight.
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NIH Publication No. 96-4158
e-text posted: 12 February 1998
Updated: June 2000
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