Obesity affects many millions of Americans and is a major public health problem. It is characterized by excess body fat caused by an imbalance between energy intake and energy expenditure (2). The specific reasons behind such an imbalance, however, remain the subject of much debate.
Genetic, environmental and behavioral variables all influence the risk of becoming overweight (2,4), but the relative importance of each remains unclear. The prevalence of obesity for different age groups in the United States is shown in Table 1. Direct assessment of body fat can be used to evaluate obesity but the procedure is mainly limited to research. For public health studies and clinical practice, simple measures such as height and weight tables, body mass index (BMI), or skinfold measurements are used. The BMI (weight in kilograms divided by the square of height in meters) is an indicator that shows the best correlation with independent measures of body fat (2,5). The use of BMI was first proposed in 1871 and was long known as the Quetelet index. It is now widely used for assessing the degree of obesity or overweight (Table 2).
Obesity is more than a problem in its own right since it is closely linked to other diseases such as hypertension, diabetes, and cardiovascular disease. Many long-term studies have shown a greater risk of these diseases with increasing levels of obesity, even when other risk factors are present (5). Later studies have refined these conclusions and have demonstrated that the distribution of fat, especially in the abdominal area, is an additional factor (5). A waist circumference of over 40 in. (102 cm) in men and over 35 in. (89 cm) in women signifies increased risk in those who have a BMI of 25.0 to 34.9.
With increasing BMI, average blood pressure and total cholesterol levels rise while average high-density lipoprotein (HDL—a protective indicator) levels fall (6). Men in the highest obesity category have more than twice the risk of hypertension and elevated cholesterol when compared with men of normal weight. Women in the highest obesity category have four times the risk of either or both of these risk factors (6). Obese individuals are also at increased risk for several other problems, including lipid disorders, type II diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea, respiratory problems, and certain cancers.
A number of efforts have been initiated to educate the public on altering behavioral risk factors such as improper dietary habits and lack of exercise. Examples include the Dietary Guidelines for Americans (Table 3), revised editions of which are periodically issued by the U.S. Department of Agriculture (USDA) (7). Recently the first federal guidelines on the identification, evaluation, and treatment of overweight and obesity in adults were released (6). These clinical practice guidelines are designed to help physicians in their care of overweight and obesity and include the scientific background for assessment as well as the principles of safe and effective weight loss. Three key indicators are recommended BMI, waist circumference, and the patient's risk factors for diseases and conditions associated with obesity. Overweight is defined as a BMI of 25.0 to 29.9 while obesity is a BMI greater than 30.0. These values are consistent with the definitions used in many other countries and support the Dietary Guidelines for Americans. A BMI of 30.0, for example, a weight of 221 lb for a 6-ft person (100 kg: 1.83 m) or 186 lb for a person of 5 ft, 6 in. (84 kg: 1.68 m) indicates about 30 lb (13.6 kg) overweight for both men and women. Highly muscular people may have a high BMI without increased health risks. For the majority, however, BMI is an excellent indicator of overall risk.
The most successful strategies for weight loss include reduction of food energy intake, increased physical activity,
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