Obesity means having too much body fat. It is different from being overweight, which means weighing too much. The weight may come from muscle, bone, fat, and/or body water. Both terms mean that a person’s weight is greater than what’s considered healthy for his or her height.
Obesity occurs over time when you eat more calories than you use. The balance between calories-in and calories-out differs for each person. Factors that might affect your weight include your genetic makeup, overeating, eating high-fat foods, and not being physically active.
Being obese increases your risk of diabetes, heart disease, stroke, arthritis, and some cancers. If you are obese, losing even 5 to 10 percent of your weight can delay or prevent some of these diseases. For example, that means losing 10 to 20 pounds if you weigh 200 pounds.
Defining Adult Overweight and Obesity
Weight that is higher than what is considered as a healthy weight for a given height is described as overweight or obese. Body Mass Index, or BMI, is used as a screening tool for overweight or obesity.
Adult Body Mass Index (BMI)
Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters. A high BMI can be an indicator of high body fatness.
- If your BMI is less than 18.5, it falls within the underweight range.
- If your BMI is 18.5 to <25, it falls within the normal.
- If your BMI is 25.0 to <30, it falls within the overweight range.
- If your BMI is 30.0 or higher, it falls within the obese range.
Obesity is frequently subdivided into categories:
- Class 1: BMI of 30 to < 35
- Class 2: BMI of 35 to < 40
- Class 3: BMI of 40 or higher. Class 3 obesity is sometimes categorized as “extreme” or “severe” obesity.
Note: At an individual level, BMI can be used as a screening tool but is not diagnostic of the body fatness or the health of an individual. A trained healthcare provider should perform appropriate health assessments in order to evaluate an individual’s health status and risks.
See the following table for an example.
|5′ 9″||124 lbs or less||Below 18.5||Underweight|
|125 lbs to 168 lbs||18.5 to 24.9||Healthy weight|
|169 lbs to 202 lbs||25.0 to 29.9||Overweight|
|203 lbs or more||30 or higher||Obese|
|271 lbs or more||40 or higher||Class 3 Obese|
BMI does not measure body fat directly, but research has shown that BMI is moderately correlated with more direct measures of body fat obtained from skinfold thickness measurements, bioelectrical impedance, underwater weighing, dual energy x-ray absorptiometry (DXA) and other methods 1,2,3. Furthermore, BMI appears to be strongly correlated with various adverse health outcomes consistent with these more direct measures of body fatness4,5,6,7,8,9.
For more information about BMI, visit Body Mass Index .
Definitions for Children and Teens
1Garrow, J.S. & Webster, J., 1985. Quetelet’s index (W/H2) as a measure of fatness. Int. J. Obes., 9(2), pp.147–153.
2Freedman, D.S., Horlick, M. & Berenson, G.S., 2013. A comparison of the Slaughter skinfold-thickness equations and BMI in predicting body fatness and cardiovascular disease risk factor levels in children. Am. J. Clin. Nutr., 98(6), pp.1417–24.
3Wohlfahrt-Veje, C. et al., 2014. Body fat throughout childhood in 2647 healthy Danish children: agreement of BMI, waist circumference, skinfolds with dual X-ray absorptiometry. Eur. J. Clin. Nutr., 68(6), pp.664–70.
4Steinberger, J. et al., 2005. Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents. Int. J. Obes., 29(11), pp.1346–1352.
5Sun, Q. et al., 2010. Comparison of dual-energy x-ray absorptiometric and anthropometric measures of adiposity in relation to adiposity-related biologic factors. Am. J. Epidemiol., 172(12), pp.1442–1454.
6Lawlor, D.A. et al., 2010. Association between general and central adiposity in childhood, and change in these, with cardiovascular risk factors in adolescence: prospective cohort study. BMJ, 341, p.c6224.
7Flegal, K.M. & Graubard, B.I., 2009. Estimates of excess deaths associated with body mass index and other anthropometric variables. Am. J. Clin. Nutr., 89(4), pp.1213–1219.
8Freedman, D.S. et al., 2009. Relation of body mass index and skinfold thicknesses to cardiovascular disease risk factors in children: the Bogalusa Heart Study. Am. J. Clin. Nutr., 90(1), pp.210–216.
9Willett, K. et al., 2006. Comparison of bioelectrical impedance and BMI in predicting obesity-related medical conditions. Obes. (Silver Spring), 14(3), pp.480–490.