## Body Mass Index

• The body mass index (BMI) or Quetelet index is a value derived from the mass (weight) and height of an individual. The BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2, resulting from mass in kilograms and height in metres.

The BMI may also be determined using a table or chart which displays BMI as a function of mass and height using contour lines or colours for different BMI categories, and which may use other units of measurement (converted to metric units for the calculation).

The BMI is an attempt to quantify the amount of tissue mass (muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value. However, there is some debate about where on the BMI scale the dividing lines between categories should be placed. Commonly accepted BMI ranges are underweight: under 18.5 kg/m2, normal weight: 18.5 to 25, overweight: 25 to 30, obese: over 30. People of Asian descent have different associations between BMI, percentage of body fat, and health risks than those of European descent, with a higher risk of type 2 diabetes and cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m2, although the cutoff for observed risk varies among different Asian populations.

The basis of the BMI was devised by Adolphe Quetelet, a Belgian astronomer, mathematician, statistician and sociologist, from 1830 to 1850 during which time he developed what he called "social physics". The modern term "body mass index" (BMI) for the ratio of human body weight to squared height was coined in a paper published in the July 1972 edition of the Journal of Chronic Diseases by Ancel Keys. In this paper, Keys argued that what he termed the BMI was "...if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity"

The interest in an index that measures body fat came with increasing obesity in prosperous Western societies. BMI was explicitly cited by Keys as appropriate for population studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnosis. Additional metrics, such as waist circumference, can be more useful.

Category BMI (kg/m2) BMI Prime
from to from to
Very severely underweight 15.0 0.60
Severely underweight 15 16 0.60 0.64
Underweight 16 18.5 0.64 0.74
Normal (healthy weight) 18.5 25 0.74 1.0
Overweight 25 30 1.0 1.2
Obese Class I (Moderately obese) 30 35 1.2 1.4
Obese Class II (Severely obese) 35 40 1.4 1.6
Obese Class III (Very severely obese) 40 1.6
Category BMI (kg/m2)
from to
Underweight 18.5
Normal Range 18.5 23
Overweight—At Risk 23 25
Overweight—Moderately Obese 25 30
Overweight—Severely Obese 30
Category BMI (kg/m2)
from to
Low 18.5
Normal 18.5 25
Obese (Level 1) 25 30
Obese (Level 2) 30 35
Obese (Level 3) 35 40
Obese (Level 4) 40
Health Risk BMI (kg/m2)
Risk of developing problems such as nutritional deficiency and osteoporosis under 18.5
Low Risk (healthy range) 18.5 to 23
Moderate risk of developing heart disease, high blood pressure, stroke, diabetes 23 to 27.5
High risk of developing heart disease, high blood pressure, stroke, diabetes over 27.5
Body Mass Index values for males and females aged 20 and over, and selected percentiles by age: United States, 2011–2014.
Source: "Anthropometric Reference Data for Children and Adults: United States" from CDC DHHS
Age Percentile
5th 10th 15th 25th 50th 75th 85th 90th 95th
Men BMI (kg/m2)
20 years and over (total) 20.7 22.2 23.0 24.6 27.7 31.6 34.0 36.1 39.8
20–29 years 19.3 20.5 21.2 22.5 25.5 30.5 33.1 35.1 39.2
30–39 years 21.1 22.4 23.3 24.8 27.5 31.9 35.1 36.5 39.3
40–49 years 21.9 23.4 24.3 25.7 28.5 31.9 34.4 36.5 40.0
50–59 years 21.6 22.7 23.6 25.4 28.3 32.0 34.0 35.2 40.3
60–69 years 21.6 22.7 23.6 25.3 28.0 32.4 35.3 36.9 41.2
70–79 years 21.5 23.2 23.9 25.4 27.8 30.9 33.1 34.9 38.9
80 years and over 20.0 21.5 22.5 24.1 26.3 29.0 31.1 32.3 33.8
Age Women BMI (kg/m2)
20 years and over (total) 19.6 21.0 22.0 23.6 27.7 33.2 36.5 39.3 43.3
20–29 years 18.6 19.8 20.7 21.9 25.6 31.8 36.0 38.9 42.0
30–39 years 19.8 21.1 22.0 23.3 27.6 33.1 36.6 40.0 44.7
40–49 years 20.0 21.5 22.5 23.7 28.1 33.4 37.0 39.6 44.5
50–59 years 19.9 21.5 22.2 24.5 28.6 34.4 38.3 40.7 45.2
60–69 years 20.0 21.7 23.0 24.5 28.9 33.4 36.1 38.7 41.8
70–79 years 20.5 22.1 22.9 24.6 28.3 33.4 36.5 39.1 42.9
80 years and over 19.3 20.4 21.3 23.3 26.1 29.7 30.9 32.8 35.2

${\displaystyle \mathrm {BMI} ={\frac {{\text{mass}}_{\text{kg}}}{{\text{height}}_{\text{m}}^{2}}}={\frac {{\text{mass}}_{\text{lb}}}{{\text{height}}_{\text{in}}^{2}}}\times 703}$
• Ferrera, Linda A., ed. (2006). Focus on Body Mass Index And Health Research. New York: Nova Science. ISBN .
• Samaras, Thomas T., ed. (2007). Human Body Size and the Laws of Scaling: Physiological, Performance, Growth, Longevity and Ecological Ramifications. New York: Nova Science. ISBN .
• Sothern, Melinda S.; Gordon, Stewart T.; von Almen, T. Kristian, eds. (2006). Handbook of Pediatric Obesity: Clinical Management (illustrated ed.). CRC Press. ISBN .
• U.S. National Center for Health Statistics:
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