Body Mass Index (BMI) is used to assess how much an
individual’s body weight departs from what is normal or desirable for a person
of his or her height. The weight excess or deficiency may, in part, be
accounted for by body fat (adipose tissue) although other factors such as
muscularity also affect BMI significantly. The World
individual’s body weight departs from what is normal or desirable for a person
of his or her height. The weight excess or deficiency may, in part, be
accounted for by body fat (adipose tissue) although other factors such as
muscularity also affect BMI significantly. The World
Health Organisation (WHO)
regards a BMI of less than 18.5 as underweight and may indicate malnutrition,
an eating disorder, or other health problems, while a BMI greater than 25 is
considered overweight and above 30 is considered obese. (WHO, 2004).
Apart from BMI, BMI Prime, a simple modification of the BMI system, which is
the ratio of actual BMI to upper limit BMI (currently defined at BMI 25) is
also used to measure whether a person is underweight, normal, overweight or
obese. As a definition, BMI Prime is the ratio of body weight to upper body
weight limit, calculated at BMI 25. Since it is the ratio of two separate BMI
values, BMI Prime is a dimensionless number, without associated units.
Individuals with BMI Prime less than 0.74 are underweight; those between 0.74
and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI
Prime is useful clinically because individuals can tell, at a glance, by what
percentage they deviate from their upper weight limits. For instance, a person
with BMI 34 has a BMI Prime of 34/25 = 1.36, and is 36% over his or her upper
mass limit. (Gadzik,
2006).
the ratio of actual BMI to upper limit BMI (currently defined at BMI 25) is
also used to measure whether a person is underweight, normal, overweight or
obese. As a definition, BMI Prime is the ratio of body weight to upper body
weight limit, calculated at BMI 25. Since it is the ratio of two separate BMI
values, BMI Prime is a dimensionless number, without associated units.
Individuals with BMI Prime less than 0.74 are underweight; those between 0.74
and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI
Prime is useful clinically because individuals can tell, at a glance, by what
percentage they deviate from their upper weight limits. For instance, a person
with BMI 34 has a BMI Prime of 34/25 = 1.36, and is 36% over his or her upper
mass limit. (Gadzik,
2006).
These ranges of BMI values are valid only as
statistical categories
statistical categories
|
Category
|
BMI range – kg/m2
|
BMI Prime
|
|
Very severely underweight
|
less than 15
|
less than 0.60
|
|
Severely underweight
|
from 15.0 to 16.0
|
from 0.60 to 0.64
|
|
Underweight
|
from 16.0 to 18.5
|
from 0.64 to 0.74
|
|
Normal (healthy weight)
|
from 18.5 to 25
|
from 0.74 to 1.0
|
|
Overweight
|
from 25 to 30
|
from 1.0 to 1.2
|
|
Obese Class I (Moderately obese)
|
from 30 to 35
|
from 1.2 to 1.4
|
|
Obese Class II (Severely obese)
|
from 35 to 40
|
from 1.4 to 1.6
|
|
Obese Class III (Very severely obese)
|
over 40
|
over 1.6
|
Source:
Adapted from WHO, 1995, WHO, 2000 and WHO 2004.
Adapted from WHO, 1995, WHO, 2000 and WHO 2004.
References
Gadzik, J. (2006). “‘How much should I weigh?’ Quetelet’s equation,
upper weight limits, and BMI prime”. Connecticut Medicine 70
(2): 81–8.
upper weight limits, and BMI prime”. Connecticut Medicine 70
(2): 81–8.
WHO (2004). WHO expert consultation. Appropriate body-mass index
for Asian populations and its implications for policy and intervention
strategies. The Lancet, 2004; 157-163.
for Asian populations and its implications for policy and intervention
strategies. The Lancet, 2004; 157-163.