Obesity is a disease characterized by abnormal or excessive fat accumulation that can impair health. It’s a global health epidemic with more than 650 million people affected worldwide, according to the World Health Organization. Obesity is a contributing factor to many diseases, including:

  • Diabetes
  • Cardiovascular disease
  • Musculoskeletal disorders
  • Certain cancers

The medical definition of obesity is based on body mass index (BMI)—your weight divided by height squared. People with a BMI of 30 or above are considered obese. Your doctor will also consider your BMI in the context of an overall health assessment.

BMI is a flawed measure that does not take into account factors such as body composition, ethnicity, sex, race, and age. Even though it is a biased measure, BMI is still widely used in the medical community because it’s an inexpensive and quick way to analyze a person’s potential health status and outcomes.

Frequently Asked Questions

  • Is obesity a disease?

    Yes, the American Medical Association (AMA) defines obesity as a disease that stems from a complex mixture of factors including genetics, environment, and behavior. It’s considered an epidemic in the United States, with more than a third of the population estimated to be obese.

  • What is considered obese?

    You’re generally considered obese if your body mass index (BMI) is 30 or higher. BMI is calculated by dividing your weight by your height squared. However, that number doesn’t take into consideration important factors such as muscle mass or frame size. Your doctor should consider the number in the context of your overall health when determining whether you’re obese.

  • What causes obesity?

    Obesity is caused by an energy imbalance between calories consumed and calories expended, although some people are more predisposed to obesity than others.

    Factors that contribute to obesity include:

  • How can I prevent obesity?

    Obesity is mostly preventable with a healthy lifestyle:

    • Eating a balanced, portion-controlled diet
    • Being active
    • Finding healthy outlets for stress
    • Getting enough sleep

    While this is especially important for those with a family history of obesity, medical conditions that contribute to weight gain, and other risk factors, everyone’s health can benefit from these strategies.

Key Terms

Page Sources
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  1. Wenker KJ, Quint JM. Ankylosing Spondylitis. In: StatPearls. Updated November 14, 2018.

  2. University Health Care System. About Morbid Obesity - What is Obesity?

  3. World Health Organization. Physical Activity.

Additional Reading