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Obesity as a health problem 

Obesity as a health problem
Chapter:
Obesity as a health problem
Author(s):

Stefan Rossner

DOI:
10.1093/med/9780199235292.003.1205
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date: 24 September 2018

Obesity is defined as an excess of body fat that is sufficient to adversely affect health. The prevalence of obesity has been difficult to study because many countries have had their own specific criteria for the classification of different degrees of overweight. However, during the 1990s, the body mass index (weight in kg/height in metres squared), or BMI, became a universally accepted measure of the degree of overweight and now identical limits are recommended. The most frequently accepted classification of overweight and obesity in adults by the WHO is shown in Table 12.1.1.1 (1).

In many community studies in affluent societies this scheme has been simplified and cut-off points of 25 and 30 kg/m2 are used for descriptive purposes of overweight and obesity. Both the prevalence of very low BMI (below 18.5 kg/m2) and very high BMI (40 kg/m2 or higher) are usually low, in the order of 1–2% or less. There are some indications that the limits used to designate obesity or overweight in Asian populations may be lowered by several units of BMI; this would greatly affect estimates of the prevalence of obesity. In countries such as China and India with each over a billion inhabitants, small changes in the criteria for overweight or obesity potentially increase the world estimate of obesity by several hundred million (currently estimates are about 250 million worldwide).

The distribution of abdominal fat should be considered for an accurate classification of overweight and obesity with respect to the health risks (Table 12.1.1.2). Traditionally this has been indicated by a relatively high waist-to-hip circumference ratio; however, the waist circumference alone may be a better and simpler measure of abdominal fatness (2). In 1998 the National Institutes of Health adopted the BMI classification and combined this with limits for waist measurement (3). This classification proposes that the combination of overweight (BMI between 25 and 30 kg/m2) and moderate obesity (BMI between 30 and 35 kg/m2) with a large waist circumference (greater than or equal to 102 cm in men or greater than or equal to 88 cm in women) carries additional risk (3).

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