Body mass index (BMI)

main measure used in international obesity management guidelines

has limitations and should not be used in isolation

less useful than waist circumference at predicting chronic disease risk

is a weight-for-height index:
o
weight (kg)/height (m)²
o
calculator click here

thresholds are the same for both sexes

based on WHO criteria:
o
<18.5 = underweight
o
18.5-24.9 = healthy weight range
o
25.0-29.9 = overweight
o
30.0-34.9 = obesity I
o
35-39.9 = obesity II
o
>40.0 = obesity III
Interpreting BMI

at a population level, increased mortality and higher incidence of disease related to
increased fat mass are seen most markedly with BMI > 35 kg/m²

individuals with the same BMI may have different ratios of body fat to lean mass

people with high muscle mass (eg athletes):
o
may have a lower proportion of body fat than less muscular people
o
a higher BMI threshold can be considered

women have more body fat than men at equivalent BMIs

a higher BMI threshold should be considered in people ≥ 65 years of age:

o
underweight ≤ 23
o
healthy weight 24-30
o
overweight > 30
Aboriginal peoples:
o
have a relatively high limb to trunk ratio and a lower BMI threshold may be
considered
o
many have proportionately more body fat that is deposited centrally:

even modest levels of overweight are associated with increased risk of
chronic disease

Pacific Islander populations (including Torres Strait Islander peoples and Maori) tend to
have a higher proportion of lean body mass:

o
a higher BMI threshold may be considered
o
under weight ≤ 19.9
o
normal 20-26.9
o
overweight 27-32.9
o
obesity ≥ 33
South Asian, Chinese and Japanese populations may have more body fat at lower weights
and be at greater risk of ill-health than other people:

o
a lower BMI threshold may be considered
o
underweight < 18.5
o
normal 18.5-23.9
o
overweight 24-26
o
obesity ≥ 27
some ethnic groups may also be more prone to visceral or subcutaneous fat accumulation at
any given BMI