What is the medical definition of obesity?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Obesity is a chronic medical condition characterized by excessive body fat accumulation that increases the risk of serious health problems, including heart disease, type 2 diabetes, high blood pressure, stroke, and certain cancers. It is typically diagnosed when a person's body mass index (BMI) is 30 or higher, though factors like waist circumference and overall health are also considered. Obesity results from a complex mix of genetic, behavioral, environmental, and metabolic factors—not simply overeating or lack of willpower.

If you're concerned about your weight or related symptoms like fatigue, joint pain, or shortness of breath, understanding the root cause is the critical first step. Take a free, instant, online symptom check to get personalized insights into what may be driving your symptoms and clear guidance on the best next steps—before small concerns become bigger health issues.

Reviewed for medical accuracy: 07/20/2026

Important Next Steps

Learn if obesity affects your health Discover likely causes of obesity symptoms See if your weight needs care Find OTC options for weight-related symptoms Find an obesity specialist near you Understand home remedies for obesity support Find out if obesity needs attention

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Explanation

Obesity is when someone has a lot of extra body fat that can make them sick. According to the medical literature, it is often measured using the Body Mass Index (BMI), which is a number calculated from a person's weight and height.

BMI Categories:
A BMI of 25 to 29.9 is considered overweight.
A BMI of 30 or higher is considered obese.

In addition to BMI, doctors may look at other factors like waist size and overall health to decide if someone is obese. Obesity can increase the risk of diseases like diabetes, heart problems, and some cancers. If you're experiencing symptoms related to weight or overall health concerns, you can check your symptoms to better understand what might be affecting you. Understanding and managing obesity is important for staying healthy.

(References)

Apovian CM. (2016). Obesity: definition, comorbidities, causes, and burden. The American journal of managed care, 27356115.
Rubino F, Cummings DE, Eckel RH, Cohen RV, Wilding JPH, Brown WA, et al. (2025). Definition and diagnostic criteria of clinical obesity. The lancet. Diabetes & endocrinology, 39824205.
Pi-Sunyer FX. (2000). Obesity: criteria and classification. The Proceedings of the Nutrition Society, 11115784.

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