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THE OBESITY EPIDEMIC AND ETIOLOGY

Obesity has been a part of human society from time immemorial. One of the earliest documented references to human obesity can be seen in a limestone female figurine from the late Paleolithic period (c. 25,000 BC) found in Willendorf, Australia, in 1908, commonly referred to as the Venus of Willendorf. She is believed to be the matriarch of fertility. As human evolution progressed from thrift to abundance, the apparent selection advantage of excess body fat (eg, insulation, protection, efficient energy storage) was replaced by the health burdens of obesity. This shift has accelerated dramatically over the past half-century, and today, obesity and its attendant metabolic consequences have become a major health crisis worldwide.

Broadly defined, obesity is the excess accumulation of body fat and is commonly accepted as a body mass index (BMI; weight/height2 [kg/m2]) of > 30. BMI was adopted by the medical community after its earlier adoption by the insurance industry for actuarial use. Although its use has many imperfections (eg, a short muscular man may be classified as overweight or obese but not be burdened by the health risks of excess body fat), its relative simplicity renders it an attractive common measurement of body weight. It is estimated that from 1970 to 2005, the prevalence of obesity in the United States more than doubled, and it has continued to rise. The Centers for Disease Control and Prevention (CDC) estimates that, as of 2016, 39.8% of American adults and 18.5% of American youth (age 2-19 years) are obese. American adults between the age of 40 and 59 years have the highest overall obesity rate at 42.8%, whereas American adolescents (age 12-19 years) have the highest youth obesity rate at 20.6%. The burden of obesity is also not distributed equally, with certain ethnic groups bearing the brunt of it. Hispanic and non-Hispanic black Americans have the highest obesity rates at 47% and 46.8%, respectively. Non-Hispanic whites have an obesity rate of 37.9%, and non-Hispanic Asians have the lowest obesity rate at 12.7%. Furthermore, the obesity rate also differs by gender, with women having higher obesity rates across all ethnic groups. Geographically, every state and territory of the United States had an obesity rate of 20% or greater in 2017, with states in the southeast bearing the heaviest burden. Although any BMI > 30 is considered obese, this is often further stratified into classes of severity. Table 46–1 summarizes the breakdown of obesity classification by BMI.

Table 46–1.Obesity classification.

Although these classifications allowed us to more precisely study the health burdens of obesity, they do not take into account the regional distribution of body fat, which has been shown to be more important than the mere volume ...

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