Class III Obesity (Formerly Known as Morbid Obesity)

Class III obesity, formerly known as morbid obesity, is a complex chronic condition that can lead to several serious health issues. There are many treatment options for class III obesity, including healthy lifestyle changes, behavioral and psychological therapy, medication and surgical procedures.


What is morbid obesity (now known as class III obesity)?

Class III obesity, formerly known as morbid obesity, is a complex chronic disease in which a person has a body mass index (BMI) of 40 or higher or a BMI of 35 or higher and is experiencing obesity-related health conditions. The BMI scale is not always accurate, so healthcare providers may use other tests and tools to assess obesity, such as measuring waist circumference.

Class III obesity can contribute to the development of several serious health conditions, such as Type 2 diabetes and heart disease. The good news is that class III obesity is manageable and treatable.


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Why was class III obesity called morbid obesity?

The term “morbid obesity” was coined by two healthcare providers in 1963 in order to justify insurance reimbursement for the cost of intestinal bypass surgery for weight loss in people with a BMI over 40.

In a medical setting, “morbidity” means illness or disease. Healthcare professionals also often use the term “comorbidity,” which means that an individual has more than one illness or disease occurring at the same time. The medical meaning of “morbid” is appropriate in describing this type of obesity since class III obesity is considered a disease and is often associated with other chronic health conditions.

The problem is that, like many words, “morbid” has another meaning. Outside of the medical setting, “morbid” means disturbing or unpleasant. Since most people aren’t familiar with the medical definition, they connected morbid (class III) obesity and people with obesity to those negative words. The use of “morbid” in describing obesity adds to the false and problematic societal stigma that suggests that people with obesity lack the willpower to lose weight, when this is almost always not the case.

Now, healthcare providers, researchers and health organizations, such as the World Health Organization (WHO), use the term “class III obesity” in place of “morbid obesity.”

What is body mass index (BMI)?

Body mass index (BMI) is a screening tool that measures the ratio of your height to your weight. Healthcare providers calculate BMI by using weight in kilograms (kg) divided by the square of height in meters (m2). In most people, BMI relates to body fat, but it’s not accurate in some cases. BMI alone does not diagnose body fatness or health. Healthcare providers use BMI and other tools and tests to assess someone’s health status and risks.

The following BMI ranges (in kg/m2) classify different weight types:

  • Underweight: Less than 18.5.
  • Optimum range: 18.5 to 24.9.
  • Overweight: 25 to 29.9.
  • Class I obesity: 30 to 34.9.
  • Class II obesity: 35 to 39.9.
  • Class III obesity: More than 40.

BMI is not always an accurate representation of an individual’s health. For example, if you have more or less muscle than what is considered optimal, your BMI may not be an accurate measurement of how much body fat you have. In addition, you could have health conditions that are highly associated with having class III obesity, such as Type 2 diabetes or high blood pressure, without having obesity.

The standard BMI scale is often not accurate for the following people:

  • Bodybuilders and professional athletes: Since muscle is more dense than fat, people who are very muscular may have a high BMI even though they have optimal levels of fat.
  • People older than 65: For people over the age of 65, it's often better to have a BMI between 25 and 27, rather than under 25. This is because a slightly higher BMI may help protect them from developing weakened bones (osteoporosis).
  • Children: While many children have obesity, you shouldn't use the standard BMI chart to evaluate a child’s weight. Talk to your child's healthcare provider about the optimum weight range for your child's age and height.

The standard BMI scale may also be inaccurate for people of different races when assessing their risk for certain health conditions. Studies have shown that, in general, people of Asian descent are more likely to have health risks at a much lower BMI, and Black people are more at risk for health issues at a higher BMI than what is considered at-risk in the standard scale.

As an example of BMI inaccuracies according to race, the standard cutoff BMI number associated with a higher risk of developing Type 2 diabetes (T2D) varies for people of different races. Differences include:

  • A BMI of 23.9 and or above is linked to a higher risk of T2D for people of South Asian descent.
  • A BMI of 26 or above is linked to a higher risk of T2D for people of Arabic descent.
  • A BMI of 28 or above is linked to a higher risk of T2D for Black people.
  • A BMI of 30 or above is linked to a higher risk of T2D for white people.


What is the difference between having obesity and having class III obesity?

In most — but not all — cases, adults with a body mass index (BMI) of 30 to 39.9 are considered to have obesity. Adults with a BMI of 40 or higher are considered to have class III obesity.

Who does class III obesity affect?

Anyone can develop class III obesity, including children and adults. However, due to its complexity, class III obesity tends to affect people differently. Based on a study on the prevalence (commonness) of class III obesity in adults in the United States between 2017 and 2018, here’s how class III obesity affects different people:

  • Sex: Approximately 11.5% of women and people assigned female at birth have class III obesity compared to 6.9% of men and people assigned male at birth.
  • Age: Class III obesity affects 11.5% of adults aged 40 to 59, 9.1% of adults aged 20 to 39 and 5.8% of adults aged 60 and over.
  • Race: Non-Hispanic Black adults had the highest prevalence of class III obesity at 13.8%, and non-Hispanic Asian adults had the lowest at 2.0%.


How common is class III obesity?

Class III obesity is a common condition. Approximately 9% of adults in the United States had class III obesity from 2017 to 2018.

Symptoms and Causes

What causes class III obesity?

Class III obesity is a complex disease that has several contributing factors. The main cause of why your body stores fat is that there’s an imbalance between the number of calories (energy) you consume and the number of calories (energy) your body uses. In other words, consuming more calories than your body uses for essential bodily processes, such as digestion and breathing, and for physical activity in a day causes your body to store fat, resulting in weight gain.

However, there are several other factors that contribute to how much food we eat, the type of food we eat and how our body uses that energy. Every person’s body is unique and metabolizes energy differently. Some people are at a greater risk of weight gain than others, and class III obesity is rarely caused by a lack of willpower to lose weight or a lack of “control” in the amount of food you eat.

Several factors contribute to developing obesity, including:

  • Genetic factors: Several studies have shown that obesity can run in families and that multiple genes are associated with weight gain.
  • Hormone imbalances: Your body makes hundreds of hormones that each have unique and important functions. Many of those hormones can affect how your body signals that you need food and how your body uses energy. For example, cortisol (often called the stress hormone) stimulates your fat and carbohydrate metabolism, creating a surge of energy in your body. While this process is essential for survival (fight-or-flight) situations, it also increases your appetite. If you experience chronic stress, it can chronically increase your cortisol levels and increase your appetite and cravings for sweet, fatty and salty foods, which can lead to weight gain. Another example is low thyroid hormone levels (hypothyroidism). Thyroid hormone is essential for maintaining your body’s metabolism. If you have lower-than-normal levels of thyroid hormone, it can slow down your metabolism and cause weight gain.
  • Socioeconomic and geographical factors: Having a low socioeconomic status and having easier financial and/or geographical access to unhealthy fast foods as compared to healthier whole foods can contribute to developing obesity. Having limited access to recreational facilities or parks and few safe or easy ways to walk in your neighborhood can also contribute to developing obesity.
  • Cultural factors: Prevalent marketing and advertising for calorie-dense foods and increased portion sizes can contribute to developing obesity.
  • Environmental factors: Exposure to chemicals known as obesogens can change your hormones and increase fatty tissue in your body.

What are the signs and symptoms of class III obesity?

There are no specific symptoms of class III obesity. The signs of class III obesity include having a body mass index (BMI) of 40 or higher and/or an unhealthy body fat distribution that healthcare providers estimate by measuring your waist circumference and skin thickness. Class III obesity can cause side effects and complications in many parts of your body.

Diagnosis and Tests

How is class III obesity diagnosed?

Healthcare providers diagnose class III obesity in part by determining a person’s body mass index (BMI). BMI is defined by the ratio of your height to your weight. Optimum BMI ranges from 20 to 25. An adult may be considered to have class III obesity if they meet one of the following criteria:

  • Are 100 pounds over the optimum body weight range for their sex and height.
  • Have a BMI of 40 or more.
  • Have a BMI of 35 or more and are experiencing obesity-related health conditions, such as high blood pressure or diabetes.

The BMI scale isn't always accurate for certain populations, and healthcare providers use a different scale to determine obesity in children.

Healthcare providers also use waist circumference measurements to help diagnose obesity.

In adults who aren't pregnant, a waist circumference over 35 inches for females or over 40 inches for males can help diagnose obesity. If you’re of South Asian or Central and South American descent, your provider may use smaller waist circumference values to diagnose obesity. People from these backgrounds often don’t show signs of a large waist circumference even though they may have unhealthy amounts of fat deep in their abdomens and may be diagnosed with obesity.

Providers can also estimate obesity by measuring skin thickness in the following areas of your body:

  • The back of your upper arms (triceps).
  • The front of your upper arms (biceps).
  • Under your shoulder blades (subscapular).
  • Above your hip bones (supra-iliac).

What tests are used to diagnose class III obesity?

Healthcare providers may order certain laboratory tests to assess your health to see if you have any health conditions that could be causing weight gain and/or that are highly associated with class III obesity. These tests may include:

Providers may also recommend other studies like an electrocardiogram (EKG) to check your heart health and sleep studies.

Management and Treatment

How is class III obesity treated?

Treatment for class III obesity is very individualized. Every person is unique and thus requires a treatment plan that’s specific to their situation and goals. Together, you and your healthcare provider can come up with a plan that treats underlying secondary causes of obesity and manages health conditions related to obesity, if you have any.

Treating class III obesity involves a multi-prong strategy. Management for class III obesity may include:

  • Healthy lifestyle changes.
  • Behavioral and psychological therapy.
  • Medications.
  • Surgical procedures.

Healthy lifestyle changes

Certain lifestyle changes can help you manage obesity, improve your overall health and/or lose weight, including:

  • Heart-healthy eating: Your healthcare provider may recommend meeting with a registered dietitian or nutritionist to learn about which foods and amounts of food are part of a healthy eating pattern. If you need to lose weight, it’s important to try to reduce your total daily calories gradually. Talk with your provider before making any drastic changes to your diet.
  • Physical activity: Physical activity has many health benefits, and it’s an important factor in determining whether a person can maintain a healthy body weight, lose excess body weight or maintain healthy weight loss. Before starting any exercise program, ask your healthcare provider about what amount and type of physical activity is right for you.
  • Healthy sleep: If you’re not getting enough sleep or have a sleep disorder, it’s essential to return to healthy sleep and/or receive treatment for sleep disorders in order to manage obesity. Lack of sleep is linked to weight gain.
  • Stress management: Chronic stress can contribute to weight gain, so it’s important to learn to cope with stress in a healthy way, such as with meditation or breathing exercises, and minimize it as much as possible.

Behavioral and psychological therapy

Your healthcare provider may recommend enrolling in individual or group behavioral weight-loss programs to help treat obesity. In these programs, a specially trained healthcare provider will customize a weight-loss plan for you.

Mood disorders, such as depression and anxiety, occur at high rates among people with obesity. Because of this, your provider may also recommend psychological therapy if you have a mental health condition.

Different types of behavioral and psychological therapies that can help treat obesity include:

  • Motivational interviewing: Motivational interviewing is a type of therapy that helps with behavior change. It’s designed to empower you to change by determining your own meaning, importance and capacity for change.
  • Cognitive behavioral therapy (CBT): In this therapy, a therapist or psychologist works with you to change your thinking and behavioral patterns that are harmful or unhelpful. CBT usually takes place over multiple sessions. Through talking and asking questions, your therapist or psychologist helps you gain a different perspective. As a result, you learn to respond better to and cope with stress, anxiety and difficult situations.
  • Dialectical behavioral therapy (DBT): This therapy is a modification of CBT. It can help if you have difficulty with emotional regulation or are exhibiting self-destructive behaviors, such as disordered eating patterns.
  • Interpersonal psychotherapy (IPT): The main goal of IPT is to improve the quality of your interpersonal relationships (relationships you have with other people) and social functioning to help reduce stress.


When healthy lifestyle changes are not enough, your healthcare provider may recommend treating obesity with FDA-approved medications. These medications work by affecting your brain or gastrointestinal tract:

  • Your brain: Several medications change the way your brain regulates the urge to eat, which can help decrease appetite. These medications include diethylpropion, phendimetrazine, lorcaserin, naltrexone/bupropion and liraglutide.
  • Your gastrointestinal tract: A medication called orlistat blocks your intestines from absorbing fat from foods in your diet. It’s usually the first choice of medications for weight loss due to having fewer side effects compared to other medications.

Weight-loss medications are not recommended as a single treatment for class III obesity. Like all medications, they have different side effects, and some should not be taken if you have certain conditions or are taking certain medications. Together, you and your provider will determine if weight loss medication is right for you.

Surgical therapy

If you have class III obesity and lifestyle changes and weight loss medications aren't working for you, you may be eligible for one of the following bariatric surgery procedures:

  • Gastric bypass surgery: In this surgery, a surgeon connects a small part of your stomach to the middle part of your intestine, bypassing the first part of your intestine. This will make you feel full with less food and limit the amount of food (calories) your body can absorb and store as fat.
  • Sleeve gastrectomy: In this surgery, a surgeon removes a big portion of your stomach, which makes you feel full with less food.
  • Gastric band surgery: In this surgery, a surgeon places a hollow band around the upper part of your stomach, which creates a smaller stomach. This will make you feel full with less food.

Surgical procedures for weight loss have certain risks and benefits. Be sure to talk to your healthcare provider about possible side effects and complications.

In general, complications that can occur shortly after surgery include:

  • Infection.
  • Postoperative bleeding.
  • Thrombosis (when blood clots block veins or arteries).
  • Cardiac events.

Longer-term complications can include:

  • Malabsorption (difficulty in the digestion or absorption of nutrients from food).
  • Vitamin and mineral deficiencies (malnutrition).
  • Refeeding syndrome (this can occur when a seriously malnourished person begins to receive nutrition again).
  • Dumping syndrome (when your stomach empties its contents into the first part of your small intestine faster than normal).
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What are the risk factors for class III obesity?

There are several risk factors for class III obesity. Some risk factors can be changed, such as lifestyle habits. Other risk factors, such as age, genetics, race and ethnicity cannot be changed. Healthy lifestyle habits can decrease your risk of developing obesity.

Risk factors for developing obesity include:

  • Certain eating behaviors: Consistently eating more calories than your body uses and eating foods high in saturated fats, trans fats and added sugar can contribute to fat storage.
  • Lack of physical activity: Having a sedentary lifestyle and not participating in frequent physical activity put you at a higher risk of developing obesity.
  • Lack of sleep: Many studies have revealed a link between high BMI and people who do not get enough sleep. Sleep loss causes a hormone imbalance in your body that promotes overeating and weight gain.
  • High amounts of stress: Chronic stress affects your brain and triggers the production of hormones, such as cortisol, that control your energy balances and hunger cues, which can make you eat more and make your body store more fat.
  • Your age: The risk of fat storage weight gain increases as you age.
  • Your sex: Females have more body fat as a percent of body weight than males from puberty onward and tend to gain more fat during their adult life than males. Going through pregnancy and menopause can also contribute to excess fat storage.
  • Your race: In the United States, rates of obesity are highest in non-Hispanic Black people, followed by Hispanic people, then white people. While people of Asian descent have the lowest rates of high BMIs, they may have high amounts of unhealthy fat in their abdomen.
  • Certain genetic syndromes: Prader-Willi syndrome, Bardet-Biedl syndrome, Alström syndrome and Cohen syndrome are associated with obesity.
  • Certain endocrine conditions: Hypothyroidism, Cushing’s syndrome and polycystic ovary syndrome (PCOS) can cause weight gain in the form of fat storage.
  • Certain medications: Antidepressants, antiepileptics, antihyperglycemics, sulfonylureas, thiazolidinediones and glucocorticoids can contribute to weight gain in the form of fat storage. Talk to your healthcare provider if you notice weight gain while you are using one of these medications. Ask if other types of medication that have less of an effect on your weight can treat your medical condition. Do not stop taking any medication without talking to your provider.

While you can’t change some risk factors for obesity, it’s important to remember that healthy lifestyle changes can help decrease your risk of developing obesity.

How can I prevent class III obesity?

If your BMI or other medical assessments indicate that you’re getting close to having obesity or if you have certain risk factors, your healthcare provider may recommend developing healthy lifestyle changes to try to prevent you from developing obesity. Lifestyle changes include:

These recommendations will be specific to your health and situation. Talk to your healthcare provider and/or a registered dietitian about setting healthy and obtainable goals.

Outlook / Prognosis

What is the prognosis (outlook) for class III obesity?

If left untreated, class III obesity may shorten life expectancy up to 14 years. In addition to contributing to potentially serious health problems, class III obesity is associated with reduced economic and social opportunities and reduced quality of life.

It is possible to treat class III obesity and improve health outcomes. Research shows that some people who have obesity and take prescription weight management medications lose 10% or more of their starting weight. Studies on bariatric surgery results have revealed that people who undergo bariatric surgery may lose 30% to 50% of their excess weight in the first six months and 77% of excess weight 12 months or more after surgery. Another study revealed that people who had bariatric surgery could maintain a 50% to 60% loss of excess weight for 10 to 14 years after surgery.

It can be daunting and overwhelming to try to lose weight and change lifestyle habits. If you have class III obesity, it’s important to remember that even a 5% to 10% weight loss from your starting weight can significantly improve your health by lowering blood sugar (glucose) levels, blood pressure and triglyceride levels. It can also improve your quality of life.

What are the complications of class III obesity?

Class III obesity is a serious medical condition that can contribute to the development of several health conditions, including:

  • Metabolic syndrome: A person has metabolic syndrome if they have a combination of at least three of the following conditions: central obesity, high triglyceride (TG) levels, low high-density lipoprotein (HDL) cholesterol levels, high blood pressure and elevated fasting blood glucose (blood sugar) levels.
  • Type 2 diabetes: Excess fat storage can lead to insulin resistance, which can lead to type 2 diabetes (T2D). The risk of developing T2D increases by 20% for each 1 point increase on the BMI scale. Many other factors contribute to the development of T2D. Not everyone who has obesity has T2D, and not every person who has T2D has obesity.
  • Heart disease: Prolonged exposure to obesity leads to worsening of cardiac (heart) function and heart disease. Having obesity can lead to having a larger ventricular mass, systolic dysfunction (impaired ventricular contraction) and atrial fibrillation (a quivering or irregular heartbeat).
  • High blood pressure (hypertension): People with obesity are 3.5 times more likely to have high blood pressure, which increases the risk of heart disease.
  • Atherosclerosis (when plaque builds up inside your arteries): Obesity is a risk factor for atherosclerosis, and can accelerate it due to other obesity-related health conditions, including high blood pressure, elevated glucose levels and systemic inflammation.
  • Certain cancers: Obesity is associated with an increased risk of 13 types of cancer. These cancers accounted for approximately 40% of all cancers diagnosed in the United States in 2014.
  • Sleep disorders, such as obstructive sleep apnea: There’s a correlation between obesity and obstructive sleep apnea (when you momentarily stop breathing while sleeping several times). In people with obesity, fat deposits in their upper respiratory tract narrow the airway, which decreases muscle activity in this area, leading to breathing issues and sleep apnea.
  • Breathing issues: Obesity hypoventilation syndrome (OHS) is a breathing disorder that affects some people who have obesity. The condition causes you to have too much carbon dioxide and too little oxygen in your blood. If left untreated, it can lead to serious and even life-threatening health problems.
  • Osteoarthritis: Having excess weight puts extra pressure on your joints, such as your knees. This makes it more likely that you'll develop osteoarthritis (OA), a degenerative joint disease, or make it worse if you already have it.
  • Depression: Approximately 43% of adults with depression have obesity, and people who have obesity have a 55% greater risk for developing depression throughout their life compared to people who do not have obesity.

Living With

How can I take care of myself if I have class III obesity?

Managing your weight or losing weight can be daunting. It’s important to remember that changing lifestyle habits takes time and patience. The following tips may help you stay committed to your health goals and lifestyle changes:

  • Set small, specific and obtainable goals.
  • Learn from your slip-ups.
  • Celebrate your successes.
  • Practice positive self-talk.
  • Get enough sleep.
  • Don’t abuse alcohol or drugs.
  • If you take prescribed medications, be sure to take them regularly and don't miss doses.
  • If you are participating in talk therapy, be sure to see your therapist regularly.
  • Reach out to family and friends for support.
  • Consider joining a support group for people who have obesity.
  • See your healthcare provider regularly.

When should I see my healthcare provider?

If you think you may have obesity or class III obesity, it’s important to see your healthcare provider so they can assess your overall health and prescribe treatment, if necessary.

If you’re having a difficult time managing your weight, contact your healthcare provider. They may run some tests to see if you have any underlying conditions that are causing weight gain.

What questions should I ask my doctor?

If you have class III obesity, it may be helpful to as your healthcare provider the following questions:

  • Do I have any health conditions that are causing weight gain?
  • Do any of my medications cause weight gain?
  • What lifestyle habits may be contributing to my health risks and obesity?
  • What can I do about the challenges I face in managing my weight?
  • Do I have any health problems that are caused by obesity?
  • What are the treatment options for obesity?
  • Should I see a dietitian or nutritionist?
  • Should I see a behavioral counselor or psychologist with expertise in weight management?
  • Is weight-loss medication or surgery an option for me?

A note from Cleveland Clinic

Class III obesity is a serious health condition that can lead to complications and a decreased quality of life. The good news is that your healthcare provider can tailor several treatment options to you and your health needs and goals. It can be daunting and challenging to try to lose weight and change lifestyle habits. Know that your medical team is there to support you in reaching your health goals.

Medically Reviewed

Last reviewed on 11/02/2021.

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