What Is Morbid Obesity?

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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.


The term “obese,” according to Stedman’s Medical Dictionary, derives from the Latin “obesus,” meaning “fat,” and is the past participle of “obedere,” which means “to eat away, devour.”

The Centers for Disease Control and Prevention (CDC)  defines obesity in adults as a body mass index (BMI) of 30.0 (kg/m2) or greater, and a BMI of 25.0 – 29.9 indicates overweight.

What Is “Morbid Obesity”?

The term “morbid obesity” refers to obesity that is “sufficient to prevent normal activity or physiologic function” (Stedman’s). Morbid obesity is usually identified at a BMI of 40.0 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 40.0 or greater, may qualify a patient for treatment with bariatric surgery (weight-loss surgery) or certain anti-obesity medications.

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 30.0 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 40.0 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 rise in BMI and extent of obesity.


Stedman’s Medical Dictionary. 25th Edition. Williams & Wilkins. 1990.

American Medical Association House of Delegates: Resolution 420 – Recognition of obesity as a disease. Accessed March 7, 2014. Jensen MD, Ryan DH, Apovian CM, et al.

Benson SS. Obesity in Tennessee: the policy implications of labeling obesity as a “disease.” Tennessee Medicine. January 2014;27-30.  

2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and The Obesity Society. Circulation. published online November 12, 2013. 

Bonow RO, Mann DL, Zipes DP, Libby P. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Ch. 79. Elsevier: Saunders, 2012.

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