Definition & Facts for Bariatric Surgery

What is obesity?

Obesity is defined as having a body mass index (BMI) of 30 or more. BMI is a measure of your weight in relation to your height. Class 1 obesity means a BMI of 30 to 35, Class 2 obesity is a BMI of 35 to 40, and Class 3 obesity is a BMI of 40 or more. Classes 2 and 3, also known as severe obesity, are often hard to treat with diet and exercise alone.

Calculate your BMI NIH external link to learn your BMI category.

What is bariatric surgery?

Bariatric surgery is an operation that helps you lose weight by making changes to your digestive system. Some types of bariatric surgeries make your stomach smaller, allowing you to eat and drink less at one time and making you feel full sooner. Other bariatric surgeries also change your small intestine—the part of your body that absorbs calories and nutrients from foods and beverages.

Bariatric surgery may be an option if you have severe obesity and have not been able to lose weight or keep from gaining back any weight you lost using other methods such as lifestyle treatment or medications. Bariatric surgery also may be an option if you have serious health problems, such as type 2 diabetes or sleep apnea, related to obesity. Bariatric surgery can improve many of the medical conditions linked to obesity, especially type 2 diabetes.