Body Mass Index (BMI): updated

Body Mass Index (BMI) measures body weight (in kilograms) against the surface area of your body measured as your height (in metres²).

In general, BMI measurements can indicate whether you are underweight, normal weight, overweight or obese.

Body mass index measurements cannot determine the lean and fat tissue composition of your body, but serve as a reasonable guide for establishing a healthy body weight range.

Being underweight, overweight or obese is associated with increased risk for a number of life limiting and/or potentially fatal health issues.

For the general population, being overweight or obese may increase the risk for heart disease, type 2 diabtetes, some cancers, sleep apnea, impaired response to certain vaccines, and mobility problems.

Being underweight through malnutrition may also increase health risks. 

Women face additonal health risks if they are underweight, overweight or obese which affect their reproductive systems, fertility, pregnancy, and birth outcomes.

Increased risk of disease has been observed below a BMI of 18.5 kg/m² and above a BMI of 30 kg/m².

For women in particular, a low body weight and BMI below 18.5 kg/m² is associated with a range of negative health issues. 

BMI measurements differ between ethnic populations and for pregnant women (or women planning to get pregnant).

Population group	Underweight	Normal/healthy weight	Overweight	Obese
Caucasian/European	< 18.5 kg/m2	18.5 kg/m2-24.9 kg/m2	25 kg/m2-29.9kg/m2	> 30kg/m2
Asian	<18.5 kg/m2	18.5 kg/m2-23 kg/m2	23 kg/m2-27.5 kg/m2	> 27.5 kg/m2
African Americans	<17.2 kg/m2	17.2 kg/m2-23.6 kg/m2	23.6kg/m2-28.6 Kg/m2	> 28.6 kg/m2
Pregnant women	< 20 kg/m2	20 kg/m2-27 kg/m2	> 27 kg/m2

A BMI measurement does not tell the whole story about your healthy body weight range.

A person with a high percentage of lean tissue (including water) may have a BMI measurement in the overweight or obese range.

Conversely, and a person with a normal BMI measurement may have a high percentage of body fat.

While a person who is underweight and has a low BMI may not be carrying excess fat tissue, that person may not have sufficient lean tissue to support good health and longevity.

Other measures are needed to more accurately determine your healthy body weight range.

These can include a simple waist measurement (waist circumference) and/or a percent body fat assessment (body composition).

To find out more about how to "get healthy" follow the links embedded in the article and browse the site to learn how eating well and incorporating physical activity into your daily routine can enhance your health and decrease your risk of chronic disease.