America is in the midst of an obesity epidemic that is rapidly growing. The prevalence of obesity increased about 50% from 1991 to 1998 . The Behavioral Risk Factor Surveillance Survey (BRFSS) for 2000 to 2001 reported the incidence of obesity increased in that one year by 5.6% . The National Health and Nutrition Examination Survey (NHANES) of 1999 and 2000 reported a national prevalence of overweight and obese adults of 64.5%, an increase from 55.9% reported in the 1988-1994 NHANES III survey .
The military must also deal with the obesity crisis. Not only are new accessions drawn from a culture that is more overweight than previous generations but the current force is also struggling with the same health problem. Dr Richard L. Atkinson, Jr announced at the 2001 American Obesity Association meeting that the proportion of overweight military men increased from 54.1% in 1995 to 58.6% in 1998, and of women from 21.6% to 26.1% .
Obesity has dramatically increased among the children and youth ofAmerica (see Chapter 5). In less than 20 years, the prevalence of obesity among children has increased 50% so that now over 15% of children aged 6 to 19 are obese . However, the disease burden is not evenly distributed. The National Longitudinal Study ofYouth reported for 1998 that 12.3% of white, 21.5% of African American, and 21.8% of Hispanic children's weights exceeded 95% of all children .
Classically, obesity is defined by calculating a certain mathematical value based on weight compared to height, called the body mass index (BMI). An overweight adult has a BMI of 25 to 29.9, and an obese adult's BMI is 30 or greater. BMI is calculated by dividing weight in pounds by height in inches twice, and then multiplying that value by 703 . For example: 200lb/68 inches/68 inches x 703 = BMI 30.4.
The significance of overweight or obese BMI is that it correlates with an increased relative risk for developing chronic diseases and cancers. The data from a 10-year follow-up of the combined Nurses' Health Study and the Physician's Health Professionals Follow-Up Study show men and women who are overweight, compared to a normal BMI of 18 to 24.9, are more likely to develop gallstones, hypertension, high cholesterol, and heart disease. The relative risk (RR) for developing diabetes of an individual with a BMI 35 or greater is 20 times greater than for someone with a normal BMI . The American Heart Association's scientific statement on obesity as an independent risk factor for heart disease states "obesity not only relates to but independently predicts coronary atherosclerosis" . The relative risk (RR) of cardiovascular death increases with BMI. A BMI of 19 to 21.9 has an RR of 1, and a BMI >32 has a RR over 3 .
An extremely high BMI has been associated with an increased risk of dying from various cancers. A prospective population of over 900,000 men and women were followed for 16 years. The data showed a BMI of at least 40 was associated with a greater risk of cancer of the esophagus, colon and rectum, liver, gallbladder, pancreas, and kidney, and death from non-Hodgkin's lymphoma and multiple myeloma. Death from all cancers combined for such men was 52% higher and for such women was 62% higher .
Finally, obesity steals years of life. Compared to a non-obese, non-smoker, the Framingham Heart Study has shown that an obese, non-smoking male will die 5.8 years earlier and an obese, non-smoking female 7.1 years earlier. At age 40, a male, obese smoker will die 13.7 years prematurely and an obese, female smoker 13.1 years prematurely . Obesity affects the majority of young and old Americans; it may well become the number one actual cause of death in the 21st century.
The current BMI definitions of overweight and obesity have limitations in the way they relate to percent body fat and the metabolic risk of other diseases and death. Multiple studies have shown that Asian populations have an increased percent body fat at a lower BMI than non-Asian populations [23,24]. To help correct this disparity, it has been suggested that a waist-to-height ratio be used to measure Asians, with 0.5 or less being a healthy value , or, alternatively, a lower BMI definition of overweight as 23 and obesity as 25 .
The increasing prevalence and health impact of obesity are staggering. With over two-thirds of Americas either overweight or obese, and with those numbers continuing to increase at a dramatic rate, it is vital that physicians be engaged in helping their patients gain control of this chronic disease. Therefore, it is important physicians understand the fundamentals of this disease and can communicate that information to their patients. To begin the process of helping overweight patients, we shall start with the physiology of obesity. Another step will be to consider how obesity can be treated as a chronic disease in the primary care setting.
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