Overweight is a state in which weight exceeds a standard based on height; obesity is a condition of excessive fatness, either generalized or localized. It is possible to be obese at a weight within normal limits according to standard tables, just as it is possible to be overweight without being obese. However, in most people, overweight and obesity tend to parallel each other.
Assessment
Underweight and obesity are assessed in a variety of ways, depending on the necessity for accuracy. The tables of the Metropolitan Life Insurance Company are widely used to establish a standard of ideal body weight (IBW). The more preferred methods include body mass index (BMI), or Quetelet Index (W/H²) in which W is weight in kilograms and H is height in meters, waist circumference, and waist–hip ratio (WHR), which compares the circumference measurements of waist and hip to identify abdominal and gluteofemoral body fat.
Excess abdominal fat is an independent risk factor of disease risk. Waist circumference over 40 in men and over 35 in women signifies increased risk in those with BMIs of 25 to 34.9 (NIH, 1998). These and other body fatness assessment methods are discussed in detail in Chapter 16. Tables for determining BMI and WHR are presented in Appendix 20 and 26, respectively.
Overweight and obesity as defined by the National Institutes of Health (NIH) are shown in Table 23–1. NIH clinical guidelines have been met with some controversy. Not all scientists support classifying individuals with a BMI of 25 as overweight. Although the risk for some comorbidities increases at BMIs less than 25, mortality does not significantly increase until BMI reaches 27 (Manson et al., 1995). Furthermore, when a BMI of 25 is used as a cutoff point, approximately half of US adults fall into the category of overweight or obese.
Risk
Obese adults are considered at risk for developing comorbidities, that is, developing other chronic diseases. A 20% increase in body weight substantially increases the risk for hypertension, coronary artery disease, lipid disorders, and non–insulin dependent diabetes mellitus. Obesity is also considered a risk factor for joint disease, gallstones, obstructive sleep apnea, and other respiratory conditions.