Severe Obesity: What You Should Know

Medically Reviewed by Zilpah Sheikh, MD on April 09, 2024
Written by Marijke Vroomen Durning, RN, Kristin Mitchell, WebMD Editorial Contributor
10 min read

Obesity is a chronic condition that's progressive and often happens again after it seemed to be resolved . It's determined by your body mass index (BMI), a measure of body fat. You calculate your BMI using your height and weight on a BMI chart. Severe obesity is defined as a BMI of 40 or greater. It's also defined by some as having a weight that is 80 to 100 pounds over what is considered your ideal body weight.

Severe obesity was formerly called "morbid obesity," but the use of this term is now discouraged, as it can be offensive. The term morbid obesity was created in 1963 as part of an effort to have weight loss surgery approved by insurance companies. 

The word “morbidity” in medical terms means something that is related to an illness or disease, but in everyday language, “morbid” means something that is unpleasant or disturbing. Now, in medical terminology, morbid obesity is called class III obesity.

A BMI number can be very different among people of the same weight. Someone who is shorter may have the same weight as someone who's taller, but the first person will probably have a higher BMI than the taller one. 

Classes of obesity

There are three classes of obesity, according to the BMI chart:

  • Obesity class I: BMI of 30 to less than 35
  • Obesity class II: BMI of 35 to less than 40‌
  • Obesity class III: BMI of 40 or higher

Class III is also categorized as “severe” obesity. It is a serious health condition that is diagnosed when someone has a BMI greater than 40, a BMI of greater than 35 with at least one serious obesity-related condition, or being more than 100 pounds over your recommended weight.

A BMI chart uses your height and weight to show how healthy your weight is. If you have a BMI of:

  • Less than 18.5, you are in the underweight range
  • 18.5 to less than 25, you are in the healthy weight range
  • 25 to less than 30, you are in the overweight range.
  • 30 or higher, you are in the obesity range

It’s important to understand that the BMI calculation is just one tool that health care providers can use to help get a picture of your health. The BMI chart doesn’t always represent health status accurately. Someone who is very muscular may weigh the same as someone who is the same height but with more fat, but they would both have the same BMI calculation. 

Using BMI for diagnosis and treatment may also cause problems for people who have eating disorders. It also doesn’t consider race, ethnicity, or sex. When the BMI chart was first designed in the 1800s, it was based on White European men only. 

Class III obesity is a disease. It happens when your body doesn’t use up all the calories you consume. The most common causes of class III obesity include:

Culture and family. Different cultures view food and obesity in different ways. Some cultures and families value heavier weight, and they may have more calorie-laden foods. Many people feel that obesity runs in their families, but it turns out that obesity is often caused not by genetics, but by social influence, as members of the same culture eat the same types of foods and do the same types of activities. 

Diet choices. Although many things can bring on obesity, the biggest is a diet that has more calories than you use up. The more calories that aren’t used, the more weight you can gain. The calories can add up quickly through not only food but also what you drink.

Lack of activity or movement. Moving helps burn calories. The more you move, the more calories you burn. If you are inactive, you will use fewer calories, which can lead to weight gain. 

Other things that can lead to class III obesity include:

Environment. Certain types of chemicals, called obesogens, can affect your body and cause obesity. There are many obesogens in the traditional Western diet. They include many food additives and preservatives, as well as pesticides used to help grow fruit and vegetables.  

Genetics. Although rare, some forms of obesity run in families. These genes affect appetite control and how food is converted into energy. 

Hormone imbalances. Certain diseases, such as hypothyroidism or Cushing’s syndrome, can cause weight gain.

Where you live. If you live in an area with limited healthy food options, you may have little choice but to eat foods that can contribute to weight gain.

Your economic status. Not having enough money to live in areas where it’s easy to get outside and exercise, join activities, or access healthy foods can also lead to weight gain.

Medications. Certain medications, especially some antipsychotics, antidepressants, and corticosteroids, as well as antihyperglycemics (drugs that lower blood sugar levels), can lead to significant weight gain.

If you have severe obesity, you may also have health conditions like:

A lower life expectancy. Overweight people can be at risk of not living as long as those in a healthy weight range. 

Type 2 diabetes. Having obesity may lead to insulin resistance, creating blood sugar levels that your body cannot maintain without the help of medication, diet changes, and loss of excess weight. 

Hypertension and heart disease. Too much weight can add stress to your heart, leaving it unable to circulate oxygen through your body. Along with high blood pressure, you may also be at risk of strokes and damage to your heart and kidneys.

Osteoarthritis. Added weight can cause your joints to wear down faster, especially around your hips and knees. Over time, chronic inflammation can lead to permanent damage and less mobility.  

Gastroesophageal reflux disease. If you have excess weight, the valve at the top of your stomach may not be able to keep acid in your stomach. If acid rises into your esophagus (the tube that links your throat to your stomach), you may have frequent heartburn. 

Depression. This condition can take a toll on your mental health. Add in the stress of multiple health conditions, and depression becomes a big concern. 

Infertility. Excess weight can affect your reproductive organs and hormone levels, which can make it difficult to conceive.‌

Urinary stress incontinence. Pressure on your kidneys and bladder can weaken your muscles, making it harder to hold your urine if you laugh, cough, or sneeze. 

Sleep apnea. Extra weight could help narrow your airway and make it harder to breathe at night. You might snore, and your breathing might stop and start while you slumber. If sleep apnea goes untreated, it can cause loud snoring, daytime tiredness, or more serious problems like heart trouble or high blood pressure.

If you have any of the health conditions above, talk to your doctor about your concerns. It’s never too late to get help. Share with them your diet and exercise habits and your efforts to maintain or lose weight.

In your conversation with your doctor, mention any eating patterns, eating disorders, or family history that may have added to class III obesity. It’s important to bring up all parts of your lifestyle so your doctor has a clear picture of your needs and can prescribe a treatment plan to help you achieve a healthy weight.‌

During a physical exam, your doctor:

  • Measures your weight and height to calculate BMI
  • Checks your vital signs, including blood pressure, heart rate, and breathing
  • Measures your waist circumference‌
  • Completes blood tests to check for health conditions like diabetes‌

Keep in mind that your waist size is also tied to increased health risks. Women with a waist size greater than 35 inches and men with a waist size of more than 40 inches are at a higher risk of health problems.

When your BMI reaches a class III obesity level, it gets harder to lose weight. ‌

Working with a certified professional to develop a plan that works for you increases your chances of success. Most of the time, insurance companies won’t pay for weight loss surgery unless you first try to lose weight on your own.

Diet. You may start with a diet plan that gives you fewer calories than you burn, but let a medical professional guide you to make sure you're still getting enough nutrition. This can result in weight loss of 1 to 2 pounds per week. ‌

Exercise. You also want to do physical activity every day. If you need to start small, that’s OK. Walk up and down your street, or park in the back of the parking lot when you go shopping. Take the stairs instead of the elevator when you can.‌

Behavioral therapy. Sometimes, old habits are so deeply set in the mind, it can be hard to change them alone. With a therapist's help, you can change harmful habits into healthy ones to promote weight loss. This is an excellent choice for identifying patterns of thought, improving emotional coping mechanisms, and working through mental health issues.

Anti-obesity medication (AOM). If you are struggling with the desire to eat more than your allotted calories for the day, your doctor may suggest a medication that blocks fat absorption or suppresses your appetite. This may help increase your success early on and produce results that are sustainable long-term. But keep in mind that these may have side effects, and it's common to gain back weight after going off of them. So following up with your weight loss team helps prevent the weight relapse.‌

Surgery. You may need bariatric and metabolic surgery to lose enough weight to reach a healthy BMI range. These surgeries work by sealing off most of your stomach, so you feel fuller faster. When you have to eat less food and feel full on less food, you lose weight faster. Many of these surgeries also remove parts of the stomach that produce hunger hormones. These typically result in rapid weight loss and require specialized diets to ensure safe nutrition.

Living with any chronic disease can be challenging. Class III obesity can pose extra problems that may affect your quality of life. These are some of the most common issues someone with obesity may face and some tips to help improve your quality of life.

  • Mental health. Having obesity can lead to depression, anxiety, and issues with self-esteem and body image. Speaking with a trained mental health professional can help you identify and manage some of these issues. Ask your doctor or local health facility for referrals to therapists or counselors who have worked with people who have obesity.
  • Activity. People with obesity are often told to get out and exercise, but people with class III obesity may find it too hard to do that. Even taking the smallest steps may seem overwhelming. First, before beginning any exercise program, speak with your doctor, who may give you suggestions or warn you away from exercises that could be harmful. If you can manage it, try taking short walks in your neighborhood, for 10 to 15 minutes perhaps, increasing your minutes as you get used to it.
  • Mobility. Moving around can be hard for people with class III obesity. If you’re finding it difficult to move around, you might benefit from a walker or a motorized scooter. If traveling, you may need to ask for accommodations, especially if you’re flying.

Weight stigma

Weight stigma, or discrimination against those who have obesity, is common. Some common examples are:

  • Comments about laziness and weight
  • Staring at someone with obesity who orders a large meal
  • Refusing to provide a larger seat or device to accommodate larger body sizes
  • Not hiring a larger person because of their weight or placing them in a role where they don’t face the public
  • Health care professionals automatically blaming a health issue on weight
  • Portraying larger characters in advertising, TV shows, or movies as buffoons or friendless

It’s not always easy fighting a stigma. If you’re comfortable doing so, you can speak up when people make unkind comments or if you know of job discrimination. But people who don't have obesity can be your allies through their actions and words, such as:

  • Discouraging unsolicited diet advice
  • Not accepting when others tell fat jokes or make comments about people who are overweight
  • Calling out others who use “fat” or weight-related words as insults
  • Avoiding using compliments based on weight, such as, “You look so great since you’ve lost weight”

Class III or severe obesity is a chronic disease that can have many causes, ranging from consuming an unhealthy diet to certain diseases or medications. Obesity stigma is real, in both personal and work life. If you have obesity, speak with your doctor to see what you can do to be as healthy as possible. It may be challenging, but slow steps can lead to great things.

  • How heavy is someone with severe obesity? Severe obesity, having a BMI of 40 or greater, is defined as being 80 to 100 pounds over your ideal body weight.

  • What is the life expectancy of someone with severe obesity? Severe obesity can cause other health problems, as well as limit activities and affect your mental health. These can all cause complications that can shorten your life. Altogether, life expectancy can be reduced by up to 14 years for people who have untreated class III obesity.

  • How can you help someone with severe obesity? You can help someone with severe obesity by being an ally. If they have goals, support them. Speak up and shut down the stigma related to severe obesity.