However, given the complexity of the relationships between weight and health outcomes, it may only be possible to develop general guidelines as to what constitute healthy weights. Care must be taken in applying weight standards to individuals, and it may not be possible to set weight goals for particular individuals by using a single table or set of cutpoints.

THE CLASSIFICATION OF OBESITY

What is a ''healthy" or "unhealthy" weight? There is no sure answer to this question. The National Institutes of Health (NIH) National Task Force on Prevention and Treatment of Obesity stated that, in general, individuals are obese if their BMI is 25 or more through age 34 and 27 or more beyond age 34 (NIDDK, 1993b). Obesity is also assessed by using weight-for-height tables. Some of the most widely used tables come from the life insurance industry, which has height, weight, and mortality data on some 5 million individuals who have chosen to obtain life insurance policies. The 1959 and 1983 Metropolitan Life Insurance Company tables of desirable weight are still among the most popular in use. In 1990, the federal government issued a table of suggested weights for adults based on height and age. Table 2-2 provides a generous range of "healthy" weights for a given height. For individuals 19-34 years of age, the BMI range given is 19 to 25; for those age 35 and older, the BMI range is 21 to 27. These figures suggest that it is acceptable for weight to increase with age (see also Andres et al., 1993), though there is disagreement about this point (see, for example, Willett et al., 1991, and Bray, 1993a). One criticism of the NIH and federal government guidelines is that they imply that it is acceptable to gain some 10–20 pounds after age 34; critics argue that individuals who gain small amounts of weight over time should learn better lifestyle habits that might eliminate or minimize weight gain. As the scientific discourse about this matter continues, we have adopted the recommendations of the NIH National Task Force.

We will often use the term comorbidity in this report to refer to the concomitant pathologic processes and diseases associated with obesity. Comorbidities linked to obesity include coronary heart disease, stroke, hypertension, obstructive sleep apnea, diabetes mellitus, gout, dyslipidemia, osteoarthritis of weight-bearing joints (such as the knees and hips), gallstones and cholecystitis, reduced fertility, reduced physical agility and increased risk of accidents, and impaired obstetrical performance (IFT, 1994; Pi-Sunyer, 1993a).

Some of these health risks of obesity are more likely to occur when fat is concentrated in the abdominal or visceral area rather than the gluteal area. A measurement called the waist-to-hip ratio (WHR) is used clinically to assess whether weight is collected primarily in the hips and buttocks (producing what is known



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