Obesity and unwanted weight gain are now recognized as a spectrum of a chronic or noncommunicable disease.¹,²,³,⁴ Unwanted weight gain leading to overweight and obesity has become a main driver of the global rise in noncommunicable diseases. Comorbidities such as type 2 diabetes mellitus, hypertension, and cardiovascular disease exact a heavy toll on overweight and obese individuals.⁵ Additionally, psychological and social effects on overweight individuals make them vulnerable to discrimination in their personal and work lives, in addition to low self-esteem and depression.⁶ All of these factors contribute to huge healthcare costs and loss of productivity as well as decreased life expectancy.

The effect of obesity on life expectancy, both on the individual and on society, frequently is underappreciated. An article in the Wall Street Journal (2018) brought this effect to the attention of the public. The article pointed out that despite total cost of health care and despite technological advances at the highest level, the United States trails other developed nations in life expectancy.⁷ The recent Global BMI Collaboration reported that obese populations have higher mortality regardless of country. Furthermore, according to the Organization for Economic Cooperation and Development (OECD) Health Statistics 2018, 40% of the US population is obese, as opposed to 17% in France, 13% in Sweden, and 4.2% in Japan, the country with the highest life expectancy.⁸

Obesity results from an interaction between a genetic predisposition to weight gain and environmental influences. Thus, there are very pronounced differences in the prevalence rates of obesity and being overweight among different populations. As will be seen below, the prevalence of obesity occurs highest in those populations most likely to present for health care at safety-net hospitals.⁹

The most accurate measures of body fat, such as underwater weighing, dual-energy x-ray absorptiometry (DEXA) scanning, computed tomography (CT), and magnetic resonance imaging (MRI), are impractical and expensive for use in most clinical encounters. Estimates of body fat, such as body mass index (BMI, calculated by dividing the body weight in kilograms by height in meters squared, or kg/m²) and waist circumference, have limitations but are easily obtained and sufficient in most situations.

Body mass index allows comparison of weights independently of stature across populations. However, it should be remembered that in certain populations, such as body builders, the standard definitions do not apply. Also, certain populations may have different thresholds for concerning BMI. In South Asians, for instance, evidence suggests that BMI-adjusted percent body fat is greater than other populations.¹⁰

In 1998, the National Institutes of Health (NIH) Expert Panel on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults adopted the World Health Organization (WHO) classification for overweight and obesity. The WHO classification, which predominantly applied to people of European ancestry, assigns increasing risk for comorbid conditions, including hypertension, type 2 diabetes mellitus, and cardiovascular disease—to persons with a higher BMI relative to persons of normal weight (BMI of 18.5-25 kg/m²). Thus it defines a BMI of 25 to 29 as overweight, a BMI of 30 as obese, and a BMI of 40 as extremely obese.¹¹

What is even more concerning is that the prevalence of obesity seems to be increasing in the United States and in the world. In 2001, the Surgeon General issued a “Call to Action” on the obesity problem, but the call drew a minimal response from the responsible federal agencies, and Americans continued to consume an average of 3800 calories per person per day or about twice the daily requirement.¹²

In the most recently published United States report (2015-2016), almost 40% of adults in this country are at a BMI ≥ 30 kg/m² and almost 20% of youth are obese.¹³

These increases represent a tripling in obesity prevalence rates of the US population since the 1960s. Interestingly, during this time, the prevalence of overweight (BMI ≥ 25 and <30 kg/m²) has remained stable in both men and women while that of extreme obesity (BMI ≥ 40 kg/m²) has undergone a ninefold increase from 0.9% in 1960 to 1962 to 8.1% in 2017. Thus currently only ˜ 30% of the US population is considered to have a healthy weight (BMI between 18.5 and 25 kg/m²).¹⁴