Body Mass Index

Body Mass Index (BMI) is used as an assessment of total body fat and is calculated as follows: BMI = weight (kg)/ height squared (m²)

Age and sex will influence BMI as a measure of total body fat:¹

• As we age BMI will underestimate total body fat since we tend to lose lean tissue and gain body fat. For men and woman with a BMI of 23 body fat will increase by 1.0-1.1% and 0.7-1.0% respectively per decade.

• Woman will have significantly greater amounts of body fat than men at equivalent BMIs. A 20 year old woman and man with a BMI of 23 would have 26.0% and 13.3% body fat respectively.

1. How useful is body mass index for comparison of body fatness across age, sex and ethnic groups? Am J of Epidemiol 1996;143:228-39