What is Obesity
Morbid Obesity
Childhood Obesity
Adult Obesity
Related Conditions
Obesity Stigmas
Causes of Obesity
Obesity in America
Obesity forecast on 2048
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What Is Obesity?

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems. Body mass index (BMI), a measurement which compares weight and height, defines people as overweight (pre-obese) when their BMI is between 25 kg/m2 and 30 kg/m2, and obese when it is greater than 30 kg/m2.

Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, breathing difficulties during sleep, certain types of cancer, and osteoarthritis. Obesity is most commonly caused by a combination of excessive dietary calories, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrine disorders, medications or psychiatric illness. Evidence to support the view that some obese people eat little yet gain weight due to a slow metabolism is limited; on average obese people have a greater energy expenditure than their thin counterparts due to the energy required to maintain an increased body mass


When you take in more calories than you burn off, you gain weight. How you eat, how active you are, and other things affect how your body uses calories and whether you gain weight.

Overweight and Obesity

American society has become 'obesogenic,' characterized by environments that promote increased food intake, non healthful foods, and physical inactivity. Policy and environmental change initiatives that make healthy choices in nutrition and physical activity available, affordable, and easy will likely prove most effective in combating obesity.

The Division of Nutrition, Physical Activity, and Obesity (DNPAO) is working to reduce obesity and obesity-related conditions through state programs, technical assistance and training, leadership, surveillance and research, intervention development and evaluation, translation of practice-based evidence and research findings, and partnership development.

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Classifications and definitions of obesity

Although several classifications and definitions for degrees of obesity are accepted, the most widely accepted is the World Health Organization (WHO) criteria based on BMI. Under this convention for adults, grade 1 overweight (commonly and simply called overweight) is a BMI of 25-29.9 kg/m2. Grade 2 overweight (commonly called obesity) is a BMI of 30-39.9 kg/m2. Grade 3 overweight (commonly called severe or morbid obesity) is a BMI greater than or equal to 40 kg/m2.

The surgical literature often uses a different classification to recognize particularly severe obesity. In this setting, a BMI greater than 40 kg/m2 is described as severe obesity, a BMI of 40-50 kg/m2 is termed morbid obesity, and a BMI greater than 50 kg/m2 is termed super obese.

The definition of obesity in children involves BMIs greater than the 85th (commonly used to define overweight) or the 95th (commonly used to define obesity) percentile, respectively, for age-matched and sex-matched control subjects.