What is Morbid Obesity?

By Zina Semenovskaya, MD
Medically reviewed checkmarkMedically reviewed
December 15, 2022

Key takeaways

  • Obesity is defined based on the body mass index (BMI).

  • The BMI is a measurement tool that divides an individual’s weight by the square of their height in meters in order to determine their approximate body fat percentage.

  • Morbid obesity, also called class 3 obesity, is a BMI classification for when an individual’s BMI is 40 or greater.

Morbid obesity, also called class 3 obesity, is a classification calculated using the body mass index (BMI) formula. People who fall into the class 3 obesity range have a BMI of 40 or higher. In general, being overweight makes you more likely to have fewer economic and social opportunities, a lower quality of life, and a higher risk of getting diabetes, high blood pressure, heart disease, and other health problems.

People with class 3 obesity may also, unfortunately, receive poor medical care. Research shows that weight bias in the medical industry makes it harder for individuals with obesity to get quality and compassionate care. If you are obese, it’s important to find a healthcare provider you trust and with whom you feel comfortable discussing your health goals.

In this article, I’ll discuss the causes and risks of class 3 obesity and weight loss strategies that can help individuals who want to lose weight.

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What is Morbid Obesity?

Morbid obesity is a classification based on the body mass index (BMI). BMIs of 40 or greater are designated as morbidly obese, or class 3 obese. Many healthcare professionals today prefer to use the term “class 3 obesity” instead of “morbid obesity.”

In the 1960s, doctors first used the term “morbid obesity” to get insurance companies to pay for the cost of gastric bypass surgeries. The word “morbid” is used in the medical community to signify illness or disease, but outside of the medical space, the word also carries negative and unpleasant connotations, which can contribute to the stigma that obese people face. 

What’s more, the word “obesity” comes from the Latin “to eat oneself fat,” which suggests that all people with obesity are wholly responsible for their weight, ignoring the biological, environmental, and genetic causes of weight. For these reasons, many people find the term “morbid obesity” to be stigmatizing. Though “class 3 obesity” still uses the word “obesity,” many providers prefer to use this term over “morbid obesity.”   

Understanding Body Mass Index

The body mass index (BMI) is a somewhat controversial calculation that was originally developed by Adolphe Quetelet, a Belgian statistician, and sociologist. He built the BMI in the 1800s as a sociology project in order to identify common characteristics of what he perceived to be the “ideal man.” The data he used to build the BMI included weight and height measurements from white, Western European men, notably excluding data from people of color and women. Unsurprisingly, the BMI fails to detect more than half of obesity cases in people of color and women, according to data from 2011. 

It’s no secret that the BMI is an imperfect and contested medical tool. But it is still used by doctors today, mostly because it is easy to understand. All you need to calculate BMI is an individual’s height and weight. Though this information can be helpful on a population level, the BMI is an unreliable measure of individual health and ignores the modern understanding of body composition. In other words, an individual’s BMI is just one component of their health. In order to get a more complete understanding of one’s health, it’s important to consider other diagnostic tools, like body composition analysis, waist circumference analysis, blood work, and more.  

What Causes Morbid Obesity?

Class 3 obesity is multifactorial, which means many factors can contribute to its development. Multiple studies have found that obesity is extremely heritable, meaning that genetics plays a key role in who develops obesity, 

Additional causes that can contribute to the development of class 3 obesity include: 

  • Reduced physical activity or exercise
  • Insomnia (a disorder marked by difficulty falling and/or staying asleep)
  • Endocrine disorders
  • Medications
  • Living in a food desert
  • Poverty
  • Decreased energy metabolism

What Risks are Associated with Morbid Obesity?

Class 3 obesity is associated with a higher risk of chronic diseases and other conditions, including:

  • Type 2 diabetes
  • Congestive heart failure
  • Chronic kidney disease
  • Certain cancers
  • Gynecological and sexual problems
  • Osteoarthritis
  • Depression
  • Breathing issues
  • Lower quality of life

How is Morbid Obesity Diagnosed?

Class 3 obesity requires the use of the BMI for diagnosis. But your doctor should offer more tests to get a more accurate and personalized analysis of your health. Further evaluation tools may include:

  • Bioelectric impedance analysis
  • Imaging scans like CTs or MRIs
  • Bone density tests
  • Water displacement test
  • Air densitometry studies
  • Laboratory tests, including:
    • Complete blood analysis
    • Basic metabolic panel
    • Renal function test
    • liver function study 
    • Lipid panel
    • HbA1C
    • TSH
    • Urinalysis 

How Do You Treat Morbid Obesity?

How you will be treated for class 3 obesity will depend on your health and medical needs. Getting the right tests done is important to having an informed conversation with your healthcare provider about your options and the right strategies for you. If you’re interested in losing weight, it’s important to speak with your provider about safe and sustainable weight loss methods. 

Making lifestyle changes

Depending on your current lifestyle habits and socioeconomic environment, making certain lifestyle changes can help improve your health and support weight loss. Chiefly, consulting with a registered dietician to come up with a customized eating plan and working with your healthcare provider to set safe and attainable physical exercise goals are two strategies that can work in tandem to improve your health and support weight loss. 

Behavioral therapy

Data shows that eating disorders contribute to 50% of cases of severe obesity. Behavioral therapy uses approaches founded in psychotherapy to help treat common eating disorders associated with obesity and repair a person’s emotional relationship with food. Approaches often used in behavioral therapy for obesity include motivational interviewing (MI), behavioral therapy (BT), cognitive therapy (CT), interpersonal therapy (IT), and acceptance-based therapy (ABT).


There are prescription medications available that are used to support weight loss in people with obesity. Examples of medications used to treat obesity include:

  • Semaglutide (Wegovy)
  • Liraglutide (Saxenda
  • Orlistat (Xenical)
  • Phentermine-topiramate (Qsymia)
  • Naltrexone-bupropion (Contrave)
  • Setmelanotide (IMCIVREE)

Before starting a new weight loss medication, it’s important to discuss the potential benefits and risks of these medications with your doctor. 

Undergoing surgery

People with class 3 obesity and severe health conditions associated with their weight may consider surgery as a treatment option. Common surgical weight loss procedures include:

  • Gastric banding
  • Rou-en-Y gastric bypass
  • Sleeve gastrectomy

Before pursuing this option, it is critical to discuss the necessary lifestyle changes and post-surgery care with your provider, as well as all of the risks associated with surgery. Surgery for weight loss is an irreversible decision that can cause complications, including infection, postoperative bleeding, malabsorption, vitamin and mineral deficiency, cardiac events, and more. 

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Obesity, including class 3 obesity, is associated with a higher risk of several serious health conditions and increased mortality, due in part to the stigmas people who are obese face when trying to access high-quality medical care. Although getting quality care if you’re obese can be difficult, it is important to ensuring that you live a healthy and high-quality life. To improve the outlook for your health outcomes, it’s important to find a healthcare provider you trust and with whom you can work together on your health goals.

Can Morbid Obesity be Prevented?

Not all cases of class 3 obesity can be fully prevented, especially those caused or exacerbated by genetics, biology, socioeconomic environment, or a combination of all three factors. But in some cases, there are some things that can help prevent class 3 obesity and manage your weight, including:

  • Eating a nutritious diet
  • Exercising regularly
  • Getting adequate, regular sleep
  • Managing stress

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Frequently Asked Questions

What qualifies as morbid obesity?
Morbid obesity, also called class 3 obesity, is a body mass index (BMI) classification. People with a BMI of 40 or greater fall into the class 3 obesity category.
What is the difference between overweight and morbidly obese?
Overweight and morbidly obese are body mass index (BMI) classifications. BMI is measured by dividing an individual’s weight by the square of their height in meters. People with a BMI of 25-29 are considered overweight, while those with a BMI of 40 or higher are considered morbidly obese.
What are the categories of obesity?
The categories of obesity according to the body mass index (BMI) are class 1 obesity, class 2 obesity, and class 3 obesity.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.

Zina Semenovskaya, MD

Dr. Semenovskaya specializes in emergency medicine, and received her medical degree from Weill Cornell Medical College. She is currently the medical director at Remote Emergency Medicine Consulting, LLC and splits her time working clinically as an emergency medicine attending in California and Alaska. She is the first of our doctors to be fluent in Russian.

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