Let's Talk About Severe Obesity

About 25% of people with obesity fall into the "severe" classification. Here's what that means and how treatment can help.

by Leslie Goldman Health Writer

It’s the food that you don’t eat in public.… It’s the scanning of the shop before you even enter, to determine if there are any clothes that may remotely fit…It’s the fear that you feel whenever sitting on a new chair, in case it breaks…It’s the terror when you have a pain in your chest: not as much because it could be a heart attack, but because people will know it’s because of your weight.

Severe Obesity

Our Pro Panel

We went to some of the nation's top experts on obesity to bring you the most up-to-date information possible.

Robert Eckel, M.D. headshot.

Robert Eckel, M.D.

Past President and Volunteer Medical Expert, Professor Emeritus

American Heart Association, University of Colorado School of Medicine

Aurora, CO

Anna Welcome, M.D.

Anna Welcome, M.D.

Assistant Clinical Professor; Fellow of the Obesity Medicine Association

Western Michigan University School of Medicine

Kalamazoo, MI

Matt Hutter, M.D., M.P.H.

Matt Hutter, M.D.

President; Professor of Surgery; Director

American Society for Metabolic and Bariatric Surgery; Harvard Medical School; American Society for Metabolic and Bariatric Surgery


Severe Obesity
Frequently Asked Questions
What are the three levels of obesity?

There are three levels, or categories, of obesity, and they are based on one’s Body Mass Index (BMI). Class 1 includes those people with a BMI of 30.0 to 34.9. Class 2 includes those with a BMI of 35.0 to 39.9. And Class 3, or severe obesity, encompasses those with a BMI of 40 or above. You can determine your BMI by dividing your weight (in pounds) by your height (in centimeters) squared. Multiply that number by 703 and you’ll have your BMI.

What causes severe obesity?

Like other classes of obesity, severe obesity is caused by a combination of genetic and environmental factors. For many people, obesity is a result of an imbalance in caloric intake and expenditure: When you consume more calories than you burn through exercise and activities of daily living, you create what is called a positive energy balance that, continued unchecked, can lead to weight gain and, possibly, obesity. Genetics also contributes to many cases of severe obesity, as does access to massive portion sizes, a lack of physical activity, and some medications.

What is the average life expectancy of a person with severe obesity?

According to a recent International Journal of Obesity study, individuals who have obesity live 5.6 to 7.6 fewer years than their healthy-weight counterparts. Those with severe obesity are more likely to die 8.1 to 10.3 years earlier.

What categorizes a person as having severe obesity?

A Body Mass Index (BMI) of 40 or higher typically categorizes someone as having severe obesity.

Those are the words of a blogger named Kate, who runs CocoGirlButter.com, describing life with severe obesity. Individuals with this serious medical condition often feel anxiety and embarrassment as they face disapproving looks from strangers, field unhelpful “suggestions” from friends and family, and cope with chronic ailments and health concerns. What causes severe obesity? How is it determined? And what hope is there for treatment? We know you have questions—and we have answers.

What Exactly Is Obesity?

Obesity is a diagnosable disease that occurs when an individual accumulates and stores excess amounts of body fat. It’s typically determined by calculating a person’s Body Mass Index (BMI)—an estimate of whether a person’s weight is healthy based on their height. How is BMI calculated? You can either use this handy BMI calculator or the calculation below:

Weight (in pounds)/Height (in centimeters) squared

Multiply that number by 703 = BMI

A BMI of 25.0 to 29.9 for adults is considered overweight by most doctors.

A BMI of 30 or more is considered obese.

BMI isn’t a perfect calculation, for one primary reason: It fails to distinguish how much muscle versus fat a person is carrying—therefore, a fit individual and a sedentary individual could have the same BMI. However, it is a good gauge of whether one’s body fat falls into the healthy range.

Get All the Details on Obesity

How Is Obesity Categorized?

Obesity is divided into three main categories, based on one’s BMI.

Class 1 = BMI of 30.0 to 34.9

Class 2 = BMI of 35.0 to 39.9

Class 3, or severe = BMI of 40 or above

You’ll often see these classes described using roman numerals, i.e. Class I, Class II, and Class III.

Because your BMI depends on your height, two people can have substantially different weights and still qualify as having severe obesity, also known as class 3 obesity. For instance, a person standing 5’4” and weighing 234 pounds has a BMI of 40, as does someone who is 5’9” and weighs 271 pounds.

How is severe obesity diagnosed? Different healthcare professionals may define it differently:

  • Having a BMI of 40 or greater (most widely used)

  • Weighing 100 pounds over your ideal body weight (with doctor can help you determine what they number is)

  • Having a BMI of 35 or more, plus at least one obesity-related health condition, such as high blood pressure or diabetes.

Additionally, someone with a BMI above 50 is considered to have super obesity. A BMI of more than 60 falls into the super-super obese category.

Learn More About Obesity & BMI

Is Severe Obesity on the Rise?

The prevalence of severe obesity has increased fivefold over the past five decades, outpacing obesity in general, which has nearly tripled in the same time frame, according to new research out of the Mayo Clinic. It’s believed that about 10% of Americans now fall into the category of having severe obesity.

Severe obesity will likely soon become the most common BMI category for women, non-Hispanic black adults, and those with annual incomes below $50,000 per year, new research published in the New England Journal of Medicine indicates. (It must be noted that these researchers, mostly hailing from Harvard T.H. Chan School of Public Health, used a BMI of 35 or greater as a cut-off for severe obesity.) Using their criteria, researchers predicted that close to one in four U.S. adults will have severe obesity by 2030, with the prevalence swelling even higher in 25 states. Super obesity is also on the rise, particularly for Americans.

What Happened to the Term Morbidly Obese?

The medical community used to use “morbid obesity” to describe people with a BMI of 40 or above. But as more and more doctors begin to adopt person-first language (i.e. we don’t call someone “obese”; we say, “a person with obesity”), they’ve also shelved the phrase “morbid obesity” due to its stigmatizing nature.

As the Obesity Medicine Association points out, the dictionary definition of morbid is “an abnormal and unhealthy interest in disturbing and unpleasant subjects,” imbuing a diagnosis of morbid obesity with a sense of horror and making patients feel judged and scorned. Considering the bias already directed at people with obesity, the medical community at large has begun shifting away from the term.

Do We Know What Causes Severe Obesity?

Like other classes of obesity, severe obesity is caused by a combination of genetic and environmental factors. And like other classes of obesity, experts have yet to pinpoint which matters more. It’s truly a nature versus nurture debate.

We know that for most people, obesity is a result of an imbalance in caloric intake and expenditure: When you consume more calories than you burn through exercise and activities of daily living, you create what is called a positive energy balance. If continued unchecked, this can lead to weight gain and, possibly, obesity.

But so many other factors come into play.

The Case for Nature

Just like tall people are more likely to give birth to tall offspring or blue-eyed parents often have blue-eyed kiddos, genetics contribute anywhere from 40% to 70% of obesity, according to the Obesity Medicine Association. Hundreds of genes are known to be strongly associated with the disease. In most cases, a person is born with multiple genes that increase, but don’t necessarily guarantee the likelihood of becoming obesity.

One such gene is known as the Fat Mass and Obesity-associated gene (FTO). All people inherit two copies of this gene (one from each parent), in the form of either a high-risk variant or a low-risk variant. Someone who inherits two high-risk copies may be up to 70% more likely to develop obesity than people with other combinations.

People with two high-risk copies have trouble limiting their caloric intake when exposed to readily accessible food. That doesn’t mean they cannot limit their intake; it means it’s trickier for them to do so compared with others. Simply because the FTO gene lives in their genetic makeup, a person may experience:

  • Increased hunger levels

  • Increased caloric intake

  • Reduced satiety

  • Reduced control overeating

  • Increased tendency to be sedentary

  • Increased tendency to store body fat

In other words, while a person’s weight isn’t completely up to fate, some of us have a genetic propensity toward gaining weight. Obesity-related genes interact with the environment to increase or decrease a person’s odds of gaining an unhealthy amount of weight. Studies involving identical twins raised in different locations bear this out, as one twin may end up with obesity while the other doesn’t, despite having the same DNA.

Very rarely, a person may be born with a specific genetic mutation that causes them to develop obesity within the first few months of life.

Additionally, research suggests that genetics may play a particularly strong role in severe obesity. Families with at least one parent with severe obesity were nearly three times more likely to have one or more grown children with severe obesity compared with the general population, one study found. Still, that study couldn’t rule out the possible influence of growing up in the same household and community environment. Which brings us to…

The Case for Nurture

Environment—the social, economic, cultural, and physical factors that surround us—has a surprisingly bold influence on our food intake, and how quickly or inefficiently we burn it off.

Living in an Obesogenic Environment

Many aspects of modern-day society conspire to propel us to eat more calories a day than needed—creating what’s called an obesogenic environment. What are the attributes of such an environment? (Hint: We live in one!)

  • Constant snacking

  • Enormous portion sizes

  • The widespread availability of highly palatable (a.k.a. irresistibly yummy) ultra-processed foods like candy, chips, soda, and fast food

  • Access to cars and public transportation, which reduces physical activity

Prescription Medications

Several prescription medications have been linked to obesity. These include:

  • Steroids

  • Antidepressants

  • Hormonal contraceptives

  • Medications for diabetes, bipolar disorder, insomnia, high blood pressure, epilepsy, and more

Poor Sleep

Consistently tucking in too late, tossing and turning—both can have a profound impact on how you feel as well as what you eat during the day. That’s because poor sleep upsets the balance between the hormones that make us feel hungry (ghrelin) and full (leptin). Too little sleep and ghrelin soars, driving us to eat more.

Severe obesity is usually the result of a stew of factors, so it’s important that you don’t blame yourself for your disease, just like you wouldn’t blame yourself for developing breast cancer or thyroid disease.

What Other Conditions Am I at Risk for If I Have Severe Obesity?

Hundreds of studies have linked obesity with more than 200 chronic diseases. As BMI rises, so does a person’s risk of developing one or more of the below obesity-linked conditions. When one’s BMI teeters near the severe obesity category, those risks increase exponentially.

Heart-related conditions. Carrying excess weight can put pressure on the heart, forcing it to work harder to send blood throughout the body. Individuals who are overweight or have obesity tend to have conditions that independently raise the risk for heart disease, such as elevated cholesterol and blood pressure. A body affected by obesity can also accumulate fat surrounding the heart, called epicardial fat, which creates scarring and inflammation, compromising this supremely important organ.

Type 2 diabetes. Up to 90% of adults with type 2 diabetes are overweight or have obesity, perhaps because excess weight causes cells to become more resistant to a hormone called insulin, which is responsible for ferrying sugar from blood to the cells, where it can be used for energy. The result is elevated blood sugar, which leads to type 2 diabetes.

Cancer. Up to 40% of all cancers are caused by, or linked with, obesity. Doctors have found links between obesity and cancers of the:

Other risks. Medical conditions connected with obesity include:

  • Osteoarthritis

  • Sleep apnea,

  • Depression

  • Heartburn

  • Infertility

  • The overall risk of early death.

According to a recent International Journal of Obesity study, individuals who have obesity live 5.6 to 7.6 fewer years than their healthy-weight counterparts. Those with severe obesity can expect to die 8.1 to 10.3 years earlier.

What Are the Treatments for Severe Obesity?

Historically, surgery has been the go-to treatment for severe obesity. Published data as well as anecdotal evidence suggests that individuals affected by severe obesity tend not to succeed in losing weight, or maintaining weight loss when achieved by diet and exercise.

The National Institutes of Health has recognized that weight loss surgery, also called bariatric surgery, is among the most effective treatments for severe obesity. Several types of bariatric procedures exist. They involve altering the anatomy of the stomach, intestines, or both, to change how food is digested. This results in decreasing the intake of calories as well as their absorption.

Two of the more common bariatric procedures used to treat severe obesity are the laparoscopic sleeve gastrectomy (a.k.a. the gastric sleeve) and the laparoscopic gastric bypass. Both are done using surprisingly small incisions and the patient usually goes home the next day.

Sleeve Gastrectomy

This procedure removes about 80% of the stomach, limiting the quantity of food that can be comfortably consumed at any given time. It also exerts a strong effect on appetite-regulating hormones, so people generally just don’t feel as hungry as they did pre-surgery. People lose about 55% of their extra weight in the year to year-and-a-half following sleeve gastrectomy.

Gastric Bypass

A surgeon essentially creates a new, much smaller stomach (about the size of an egg), then connects it directly to the small intestine. The first step reduces the amount of food that can be comfortably consumed, and the second step prevents the body from absorbing as many calories as it otherwise would. People lose about 73% of their extra weight in the year to year-and-a-half following gastric bypass.


Some patients with severe obesity may instead be prescribed specific weight loss medications. Several anti-obesity medications (AOMs) have been approved by the Food and Drug Administration for weight loss and chronic weight management. These include Qsymia, Saxenda, and Contrave. Prescription AOMs work in several different ways. Some may make you feel less hungry; cause you to feel fuller, sooner; or may make food taste less appealing. Others can make it more difficult for the body to absorb fat or may ramp up your metabolism, causing you to burn more calories.

Whether you go the medication or surgical route, proper nutrition and exercise are still essential. If you have severe obesity, don’t begin a vigorous physical activity program without first consulting your physician. She or he may recommend you wait until you’ve lost 10 percent of your weight, in case you have heart disease, arthritis, or another obesity-related condition that could be aggravated by exercise.

Speaking of physicians, look for a compassionate, empathetic doctor who has experience treating extreme obesity. Ask your primary care physician for recommendations; ask friends who also have extreme obesity; or visit the American Society for Metabolic & Bariatric Surgery or the Obesity Medicine Society, both of which have tools to help you search for experienced local providers.

Leslie Goldman
Meet Our Writer
Leslie Goldman

Leslie Goldman is a health and wellness writer who regularly contributes feature stories and essays to O: The Oprah Magazine, Women’s Health, Parents, Better Homes and Gardens, and more. She has authored and contributed to several books, including Locker Room Diaries: The Naked Truth About Women, Body Image, and Re-Imagining the “Perfect” Body and Brave Girls: Raising Young Women with Passion and Purpose to Become Powerful Leaders. Leslie also speaks at colleges and universities on the topics of body image, media literacy and female empowerment.