Severe or morbid obesity: Risk factors and complications

Obesity is a condition that’s marked by having an excessive amount of body fat. It’s linked with serious health issues, such as heart disease, high blood pressure and type 2 diabetes. Severe obesity, also known as class III obesity and formerly called morbid obesity, is the most serious form of the condition, and it comes with the greatest health risks.

Obesity occurs when your weight is a certain amount higher than what is considered healthy for your height. The condition can be caused by diet, activity and sleep patterns. Genetics and certain medications can also play a role. While there are no specific symptoms of obesity, diagnosis is often based on medical history and body mass index (BMI). This is a screening tool used to estimate body fat in adults. BMI is your weight in kilograms divided by the square of your height in meters. As your BMI increases, so do your health risks. Ranges for BMI include:

• Underweight: BMI of less than 18.5
• Healthy weight: BMI of 18.5–24.9
• Overweight: BMI of 25–29.9
• Obese: BMI of 30 and higher

A BMI of 30 or above is generally considered obese. Obesity is further divided into subcategories. The different levels of obesity include:

• Class I obesity: BMI of 30–34.9
• Class II obesity: BMI of 35–39.9
• Class III obesity: BMI of 40 and higher

You may be considered severely obese if your BMI is 40 or greater. While this was previously called morbid obesity, healthcare providers and organizations now use the term severely obese or class III obesity to refer to this category.

People who are overweight have a lower BMI than those who are obese. A BMI of 25–29.9 indicates overweight, and a BMI of 30 or greater indicates obesity.

Obesity usually occurs due to a combination of genetic, behavioral and environmental factors, including:

• Genetics and family influences. Obesity can run in families. Genes may influence the amount of fat you have and where you carry it on your body. What’s more, family members also tend to share unhealthy lifestyle habits that can contribute to obesity.
• Lifestyle habits. An unhealthy diet low in fruits and vegetables and high in calories, processed foods and added sugars is associated with obesity. A lack of physical activity and a sedentary lifestyle that includes a lot of time spent in front of screens can lead to obesity.
• Environmental factors. Obesity is also linked with a low socioeconomic status, living in an unsafe location, limited access to safe recreational facilities, and easy access to unhealthy foods.
• Age. Obesity can occur at any age, even in children. But the risk of obesity increases with age. This may be due to a loss of muscle mass that often comes with age. Reduced muscle mass often leads to a slower metabolism, which can make it hard to keep weight off.
• Certain health conditions, such as Prader-Willi syndrome and Cushing syndrome, may cause obesity. Conditions that cause a reduced activity level, including arthritis, may also increase the risk of obesity.
• Some medications can cause weight gain as a side effect. Examples include antidepressants, anti-seizure medications, diabetes medicines, antipsychotic drugs, steroids and beta blockers.
• Other factors, such as poor sleep habits and high levels of stress, may also contribute to obesity.

Carrying excess weight is linked with serious medical problems, such as:

• Heart disease
• Stroke
• High blood pressure
• High cholesterol
• Type 2 diabetes
• Sleep apnea and breathing issues
• Gallbladder disease
• Osteoarthritis
• Certain types of cancer, such as endometrial, liver and kidney cancers
• Depression, anxiety and other mental health conditions
• Sexual problems, such as infertility and irregular periods in women and erectile dysfunction in obese men
• Low quality of life
• Body pain, trouble with physical functioning and disability
• Early death

There is no one-size-fits-all approach to treating obesity. Your treatment depends on the cause and severity of your condition and if you have other health issues. The goal of treatment is to reach and maintain a healthy weight. This can reduce your risk of obesity-related health issues. Note that even a modest weight loss of 5% to 10% of your body weight can cut your risks. Treatment will likely include changing your eating habits, increasing your activity level and modifying other behaviors.

Weight management programs can also help people achieve success. Working with a team of healthcare providers, including a registered dietitian, behavioral counselor and obesity medicine specialist, may also help.

Sometimes, lifestyle changes alone aren’t enough to meet weight loss goals. In these cases, your healthcare provider may recommend weight loss medicine, devices or recommend surgery. Bariatric surgery for severe obesity is common and is often considered one of the more effective obesity treatments. However, surgery also tends to come with more risks than other treatments.

Discuss your treatment options with your healthcare provider. Together, you can come up with a plan to lower your weight and your health risks.

Clinically reviewed and updated October 2023.