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Extensive weight gain is a major health problem today in many affluent societies. The Centers for Disease Control and Prevention (CDC) (2020) reported the prevalence in the United States during 2017 to 2018 to be 42 percent among all adults. The adverse health aspects of obesity are staggering and include increased risks for type 2 diabetes, heart disease, hypertension, and osteoarthritis. Importantly, obese women and their fetuses are predisposed to numerous pregnancy-related complications and to long-term morbidity and mortality.


Definitions and Prevalence

Of systems to classify obesity, the body mass index (BMI), also known as the Quetelet index, is most often used. The BMI is calculated as weight in kilograms divided by the square of the height in meters (kg/m2). Calculated BMI values are available in various chart and graphic forms (Fig. 51-1). The National Institutes of Health (2000) classifies adults according to BMI as follows: normal is 18.5 to 24.9 kg/m2, overweight is 25 to 29.9 kg/m2, and obese is ≥30 kg/m2. Obesity is further divided into: class 1 is 30 to 34.9 kg/m2, class 2 is 35 to 39.9 kg/m2, and class 3 is ≥40 kg/m2. Class 3 obesity is often referred to as morbid obesity, and supermorbid obesity describes a BMI ≥50 kg/m2.


Chart for estimating body mass index (BMI). To find the BMI category for a particular subject, locate the point at which the height and weight intersect.

Using these definitions, from 2015 to 2016 in the United States, among girls and women, the prevalence of obesity rose with age and varied among ethnicities (Fig. 51-2) (Centers for Disease Control and Prevention, 2020). Overall, severity also advances with increasing poverty. Last, a genetic predisposition has been identified (Locke, 2015; Shungin, 2015).


Prevalence of obesity in the United States by race: United States 2015–2016.

Adipose Pathophysiology

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 specifically termed adipokines, lipokines, and exosomal microRNAs (Scheja, 2019). Some of these with metabolic functions include adiponectin, leptin, tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), resistin, visfatin, apelin, vascular endothelial growth factor (VEGF), lipoprotein lipase, and insulin-like growth factor. Adiponectin is a principal adipokine. It enhances insulin sensitivity, blocks hepatic glucose release, and has cardioprotective effects on circulating plasma lipids. An adiponectin deficit is linked with diabetes, hypertension, endothelial cell activation, and cardiovascular disease.

Cytokines that result in ...

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