Obesity used to be understood in fairly simple terms, excess body weight resulting from eating too much and exercising too little, due in large part to a lack of willpower or self-restraint. Fortunately for the millions of American adults who are overweight, obesity is now regarded as a chronic medical disease with serious health implications caused by a complex set of factors.

Recognized since 1985 as a chronic disease, obesity is the second leading cause of preventable death, exceeded only by cigarette smoking. Obesity has been established as a major risk factor for hypertension, cardiovascular disease, diabetes mellitus and some cancers in both men and women. Obesity affects 58 million people across the nation and its prevalence is increasing. Approximately one-third of adults are estimated to be obese.

Obesity results from a complex interaction of genetic, behavioral and environmental factors causing an imbalance between energy intake and energy expenditure. According to the National Institutes of Health, an increase in body weight of 20 percent or more above desirable weight is the point at which excess weight becomes an established health hazard. Lower levels of excess weight can also constitute a health risk, particularly in the presence of other disorders like diabetes, hypertension and heart disease.

What are the Health Implications of Obesity?

Obesity has been established as a major risk factor for diabetes, hypertension, cardiovascular disease and some cancers in both men and women. Other comorbid conditions include sleep apnea, osteoarthritis, infertility, idiopathic intracranial hypertension, lower extremity venous stasis disease, gastro-esophageal reflux and urinary stress incontinence.

Obesity-related medical conditions contribute to 300,000 deaths each year, second only to smoking as a cause of preventable death. (JAMA, 1996; 276:1907-1915)

The estimated number of annual deaths attributable to obesity among US adults is approximately 280,000 based on relative hazard ratio from all subjects and 325,000 based on hazard ratio from only non-smokers and never-smokers. (JAMA, 1999; 282: 1530-1538)

One-third of all cases of high blood pressure are associated with obesity, and obese individuals are 50% more likely to have elevated blood cholesterol levels. (American Family Physician 1997; 55(2): 551-558)

Adult onset diabetes (type II, non-insulin dependent) accounts for nearly 90% of all cases of diabetes. Researchers estimate that 88 to 97% of type II diabetes cases diagnosed in overweight people are a direct result of obesity. (Shape Up America, December 1995)

Excess weight is an established risk factor for high blood pressure, type 2 diabetes (adult-onset), high blood cholesterol level, coronary heart disease and gallbladder disease. (JAMA, 1999; 282:1523-1529)

How is Obesity and Health Risk Measured?

Currently, several different measures are used to evaluate a patient's weight status and potential health risk. However, a complete evaluation includes assessments of a person's age, height and weight, fat composition and distribution, and the presence or absence of other health problems and risk factors.

Height-weight tables indicating "ideal" weight have been in use since 1959 but have their shortcomings. A newer measure of obesity that is gaining in popularity among researchers and clinicians is the body mass index (BMI). BMI is the body weight in kilograms divided by the square of the height in meters ([weight in kg] ÷ [height in meters] 2). BMI does not actually measure body fat, but generally correlates well with the degree of obesity. The categories of obesity developed by the World Health Organization are:

• BMI 25 to 29.9 - Grade 1 obesity (moderate overweight)
• BMI 30 to 39.9 - Grade 2 obesity (severe overweight)
• BMI > 40 - Grade 3 obesity (massive/morbid obesity).

Using a BMI table, a person 5'6" tall weighing 140 pounds would have a BMI of 23, well out of the range of risk. That same 5'6" person weighing 190 pounds would have a BMI of 31, in the range of Grade 2 obesity.

A BMI of 27 or higher is associated with increased morbidity and mortality; this is generally considered the point at which some form of treatment for obesity is required. A BMI between 25 and 27 is considered a warning sign and may warrant intervention, especially in the presence of additional risk factors.