Of systems to classiy obesity, the body mass index (EM), also known as the Quetelet index, is most oten used. The BMI is calculated as weight in kilograms divided by the square of the height in meters (kg/mr). Calculated BMI values are available in various chart and graphic forms (Fig. 48-1). The National Institutes of Health (2000) classiies adults according to BMI as follows: normal is 18.5 to 24.9 kg/mr, overweight is 25 to 29.9 kg/mr, and obese is �30 kg/mr. Obesity is urther divided into: class 1 is 30 to 34.9 kg/mr, cass 2 is 35 to 39.9 kg/mr, and cass 3 is �40 kg/mr. Class 3 obesity is oten referred to as morbid obesity, with super-morbid obesiy describing a BMI �50 kg/mr.
Using these deinitions, from 2011 to 2014, slightly more women than men were designated obese-36 versus 34 percent (Ogden, 2015). Among girls and women, the prevalence of obesity rises with age and varies among ethnicities 48-2). lthough obesity is now common among all socioeconomic levels, the overall severity advances with increasing poverty (Bilger, 2017). Also, a genetic predisposition has been identiied from several gene loci (Locke, 2015; Shungin, 2015).
Fat tissue is much more complex than merely its energy storage function. Many fat tissue cells communicate with all other tissues via endocrine and paracrine factors, which are cytokines speciically termed adipocytokines. Also simply called adipokines, some of these with metabolic functions include adiponectin, leptin, tumor necrosis factor-a (TNF-a), interleukin 6 (IL-6), resistin, visfatin, apelin, vascular endothelium growth factor (VEGF), lipoprotein lipase, and insulin-like growth factor. A principal adipokine is adiponectin, which is a 30-kDa protein. It enhances insulin sensitivity, blocks hepatic glucose release, and has cardioprotective efects on circulating plasma lipids. An adiponectin deficit is linked with diabetes, hypertension, endothelial cell activation, and cardiovascular disease.
Cytokines that result in insulin resistance are leptin, resistin, TNF-a, and IL-6, and higher levels of these are found during pregnancy. Indeed, adipokines, especially the inflammatory cytokines, may be the primary stimulant of insulin resistance