Understandig Morbid Obesity

Obviously, we hear a lot about the obesity epidemic these days. Given the wealth of information and ongoing research into the causes and management of obesity, it is helpful to have a working understanding of some of the terms that get thrown around when talking about overweight and obesity.

Overweight couple embraces on a field
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The Centers for Disease Control and Prevention (CDC) defines obesity in adults as a body mass index (BMI) of 30 (kg/m2) or greater and a BMI from 25 to 29.9 as being overweight.

What Is “Morbid Obesity”?

The term “morbid obesity” refers to obesity that is “sufficient to prevent normal activity or physiologic function,” according to Stedman's Medical Dictionary. Morbid obesity is usually identified as a BMI of 40 or greater.

Obesity as a Disease

In 2013, the American Medical Association (AMA) officially declared obesity to be a disease, acknowledging the “enormous humanitarian and economic impact of obesity as requiring the medical care, research, and education attention of other major global medical diseases.”

The impact of officially acknowledging obesity as a chronic disease is expected not only to raise awareness of the problem among the general public but also to impact policy at all levels. The hope is that policymakers will feel a greater need to fund and implement obesity treatment and intervention programs, while third-party payers will become more likely to reimburse physicians and other healthcare professionals for treatment and management of obesity as a recognized disease.

Why Do These Definitions Matter?

BMI measurements are used as part of guideline-based criteria to determine which patients may be eligible for weight-loss surgery or weight-loss medications. Thus, the diagnosis of “morbid obesity,” based on a BMI measurement of 40 or greater, may qualify a patient for treatment with bariatric surgery (weight-loss surgery) or certain anti-obesity medications. More recently, bariatric surgery may also be considered for a BMI of 35 or greater when there are medical conditions present that are caused or made worse by obesity.

Another use of the BMI measurement is to define class I, class II, and class III obesity. According to new national guidelines, having a BMI from 30 to 34.9 places a patient in the “class I obese” category; a BMI from 35.0 to 39.9 identifies the “class II obese” category; and a BMI of 40 or greater identifies the “class III obese (extreme obesity)” category.

Such measurements can also indicate level of risk for obesity-related disorders, such as cancer, cardiovascular disease, heartburn, obstructive sleep apnea, and Type 2 diabetes, since the risk of many of these disorders rises in proportion to the rise in BMI and extent of obesity.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Defining adult overweight & obesity. Updated June 7, 2021.

  2. Penn Medicine, Princeton Health. Everything you should know about morbid obesity.

  3. Kyle TK, Dhurandhar EJ, Allison DB. Regarding obesity as a disease: Evolving policies and their implications. Endocrinol Metab Clin North Am. 2016;45(3):511-520. doi:10.1016/j.ecl.2016.04.004

  4. University of Rochester Medical Center. What is morbid obesity?

  5. National Heart, Lung, and Blood Institute. Overweight and obesity.

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