Clinically severe obesity, or morbid obesity, can increase the risk of a range of other health issues. For an adult, a doctor may classify morbid obesity as having a body mass index (BMI) of 40 or above.

For an adult, having clinically severe, or class 3, obesity involves having a body mass index (BMI) of 40 or above and a high percentage of body fat.

BMI is not a diagnostic tool, but it can indicate the risk of developing various health issues.

Having severe obesity can make it difficult to do everyday activities, such as walking, breathing, and sleeping. It can also increase the risk of cardiovascular disease, type 2 diabetes, and various other health conditions.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, around 1 in 13 people in the United States had severe obesity in 2013–2014.

Below, learn more about what clinically severe obesity is and which treatments are available.

Share on Pinterest
Cláudio Policarpo/EyeEm/Getty Images

When an adult has severe obesity, they have a high percentage of body fat and a BMI of 40 or above. BMI is a scale that helps medical professionals tell whether a person has a risk of developing certain health conditions.

The following chart shows different classifications of BMI:

Under 18.5Underweight
18.5 to less than 25Moderate weight
25 to less than 30Overweight
30 to less than 35Class 1 obesity
35 to less than 40Class 2 obesity
Above 40Class 3 obesity

Here, find a BMI calculator and more information about BMI.

A person with obesity has a greater risk of heart disease and other conditions. The higher the class of obesity, the greater the likelihood of developing these complications.

However, it is worth noting that a person’s BMI does not necessarily indicate whether they have a healthy weight. It does not reflect the percentage of muscle mass compared with the percentage of fat in the body.

How useful is BMI as a tool for measuring weight and health?

Checking a person’s waist-to-hip ratio and the distribution of fat in their body can give a better idea of their risk of developing complications. Scientists have linked a high waist circumference due to body fat with a greater risk of cardiovascular disease.

Certain factors can influence the risk of developing any class of obesity. For example:

  • Dietary habits and activity levels can affect a person’s levels of energy.
  • Socioeconomic conditions can limit access to fresh food and the ability to exercise.
  • Genetic factors may play a role.
  • Family history may contribute, through both genetic and environmental factors.
  • Some medical conditions have links with obesity, including Cushing’s syndrome and polycystic ovary syndrome.
  • Stress and anxiety can increase levels of the hormone cortisol, which can affect fat storage and weight gain.
  • A lack of sleep may contribute.

Do social factors affect the risk of obesity?

The authors of a 2017 review of studies from around the world suggest that the following social factors, among others, may play a role:

  • stress due to trauma, relationship problems, financial difficulties, or a combination
  • levels of health and dietary awareness
  • workplace settings, including working hours and the likelihood of eating takeout
  • access to and availability of healthy food
  • access to green space and other considerations involving urban living and activity levels

According to the Centers for Disease Control and Prevention (CDC), obesity affects around 49.6% of Black people, 44.8% of Hispanic people, and 42.2% of white people in the U.S.

However, a 2017 survey published by CDC reveals a more nuanced picture, indicating that the prevalence of obesity varies according to combinations of factors such as education level, income, gender, and race. The relationships among these factors appear to be complex.

A person with obesity may experience:

  • sweating
  • tiredness
  • joint and back pain
  • difficulty breathing
  • sleep problems, including snoring
  • difficulty with physical activity
  • low confidence and feelings of isolation
  • high blood pressure and other symptoms of metabolic syndrome
  • symptoms of other complications, which we describe below

Indications of severe obesity include:

The complications of obesity can include:

These conditions can affect a person’s life expectancy and quality of life.

If a person visits their doctor with concerns about their weight or BMI, the doctor will likely:

  • measure their weight and height to confirm their BMI
  • ask about dietary and exercise habits
  • consider the person’s individual and family medical histories
  • do blood tests to look for health conditions that may underlie obesity
  • test for complications that may need medical attention, such as high blood pressure

If a person has severe obesity or complications relating to it, a doctor may:

  • recommend an appropriate weight loss plan
  • work with the person to develop an exercise plan
  • recommend a physical therapy plan if the person has limited mobility
  • prescribe medication, such as orlistat (Alli), which reduces the amount of fat that the body absorbs
  • recommend bariatric surgery, if other options do not help
  • address any complications, such as type 2 diabetes and other features of metabolic syndrome

A person should work with their doctor or a nutritionist to develop a suitable plan and follow the instructions carefully. Losing weight too rapidly or starting vigorous exercise too quickly can have negative effects.

Also, various weight loss drugs are available online, but they may not be safe or effective.

If other options do not help, the doctor may recommend surgery. Some of these procedures include:

  • gastric banding, in which a surgeon places a ring around the stomach, limiting the amount of food that can enter
  • gastric bypass, which aims to increase the feeling of fullness and lead to the absorption of fewer calories
  • sleeve gastrectomy, in which the surgeon removes part of the stomach
  • intragastric balloon, a temporary measure in which the surgeon places a balloon in the stomach to take up space

If a person loses a significant amount of weight, they may have unwanted folds of skin. Surgery can also address this.

Find out more about treatments for obesity.

There is no single way to lose weight or prevent weight gain. The best option will depend on the individual. However, dietary strategies and exercise can help.

Dietary tips can include:

  • consuming plenty of fresh fruits and vegetables
  • favoring whole or unprocessed foods
  • avoiding trans fats and saturated fats and opting for healthy fats, such as from safflower or corn oils
  • limiting the intake of sugar and sweetened foods
  • monitoring the caloric intake, if a healthcare professional recommends this
  • using a smaller plate
  • eating only at regular times
  • eating more slowly
  • avoiding triggers and habits that lead to overeating, such as having some cake with coffee at break times

Current guidelines recommend that, when possible, adults get at least 150 minutes of moderate-intensity activity a week. This could include walking, swimming, or cycling, for example. It might involve 10-minute sessions several times a day on most days of the week.

A doctor can advise about how much and what type of exercise a person should do, depending on their overall health, age, and other factors.

How can walking help a person lose weight?

Severe obesity is not an illness, but it can increase the risk of a wide range of health conditions, some of which can be life threatening. In most cases, severe obesity is reversible.

Anyone who has concerns about obesity or its possible symptoms should receive medical advice. Treatments can enable a person to adjust their weight and may help prevent potentially serious complications.