There are two important waist metrics which are complementary to BMI. They are waist circumference and waist to height ratio.
BMI is the most important and widely-used tool in the world for indicating fat levels in the human body, and it is officially recognised by the World Health Organisation1. However, while BMI is an indicator of total fat levels, it provides no indication of how fat is distributed in the body. The manner in which fat is distributed in the body is important, as it has been found that fat which is stored in and around internal organs (such as the liver, kidneys, pancreas and heart) tends to be significantly more harmful than fat which is stored peripherally, particularly in the form of subcutaneous (under the skin) fat.
People who store fat around internal organs can have a familiar ‘apple’ shape, while those who store fat peripherally can have what is termed a ‘pear’ shape. ‘Apple’ shaped people store fat centrally (around the waist), while ‘pear’ shaped people store fat peripherally (around the hips and buttocks). These shapes become more obvious and pronounced in the overweight and obese categories of BMI.
An apple shaped person of the same gender, age and ethnicity as a pear shaped person, and with the same BMI, will tend to have a much greater risk of developing cardiometabolic diseases such as diabetes, dyslipidaemia, hypertension, coronary heart disease and stroke. The reason for this is that internal, visceral fat is more metabolically active than subcutaneous fat, and this activity can have harmful effects such as induced insulin resistance, impaired vascular function and inflammation2.
The following waist metrics provide an indication of the extent of central fat distribution, and for this reason they are a valuable complement to BMI. However, they are not a substitute for BMI. While waist metrics take fat distribution into account and BMI does not, BMI takes total fat into account while waist metrics do not. So, when used together, these measures tend to provide a more reliable indicator of cardiometabolic risk than either measure used alone.
Waist circumference has a direct correlation with the risk of developing cardiovascular disease3. Correlations have also been established between waist circumference and the risks of developing other metabolic diseases, including type 2 diabetes4, hypertension5, certain types of cancer6 and kidney disease7. The greater the circumference of your waist, particularly when associated with a pronounced ‘apple’ shape, the greater your morbidity and mortality risks are.
Waist circumference in its own right is an indicator of the relative risks of developing cardiometabolic diseases. This is due to waist circumference tending to be a reliable proxy for central obesity. In order to mitigate these risks it is important that we maintain a healthy waist circumference.
A healthy waist circumference differs markedly between males and females. The following table details the recommended limits of waist circumference set by the World Health Organisation for both males and females, and specifies the corresponding risk categories for metabolic disease:
|Waist Circumference Limits and Risk Categories|
|Metabolic Risk Category||Males: Waist Circumference||Females: Waist Circumference|
|Normal||Less than or equal to 94 cm||Less than or equal to 80 cm|
|Increased Risk||Greater than 94 cm||Greater than 80 cm|
|Greatly Increased Risk||Greater than 102 cm||Greater than 88 cm|
The message in these numbers is clear. Men should strive to maintain a waist circumference of 94 cm or less, and for women the corresponding goal is 80 cm.
While waist circumference is a reliable indicator of cardiometabolic risk in defined populations, it has been found that a healthy waist circumference in one ethnic group can differ from that in another. For example, Asians have a higher metabolic risk than Europeans at any given waist circumference8, due to the fact that Asians tend to carry more truncal fat than Europeans for any given BMI. Consequently a more advanced and universal measure than simple waist circumference has been developed which tends to be independent of ethnicity.
This measure is waist to height ratio9, and it is calculated as waist circumference divided by height. The ratio is independent of the units of measurement used, provided that the units used to measure waist circumference are the same as those used to measure height. A number of studies have shown that waist to height ratio can be applied as a screening tool for cardiometabolic diseases across a range of populations10, and that the same boundary ratio can be used for all.
The following formula for the calculation of waist to height ratio specifies the ratio below which waist circumference is considered to be healthy. The formula is independent of ethnicity and gender:
The message in the formula is clear: men and women should strive to keep their waist circumference to no more than half their height.
While measurement of height is more or less straightforward, measurement of waist circumference is not. The important skill in measuring your waist is the ability to reproduce the measurement again and again, as significant variations will make it difficult to track changes and is more likely to result in you giving up on measuring at all. Use the following steps to correctly measure your waist:
Use a flexible but not a stretchable tape.
Measure directly on your skin, not over your clothing.
Measure in front of a mirror. It helps to ensure that the tape is horizontal and correctly placed.
Stand up straight and place the tape horizontally around your waist, immediately above your umbilicus (belly-button).
Hold the tape lightly so as not to compress your skin.
When you are ready, relax your muscles, breath out and measure.
Keep a record of your measurements if you plan to track your progress over time.
For measurements taken over a period of time, measure your waist at the same time of day.
The information in this page is not intended to provide, and is not a substitute for, medical advice of the type provided by qualified medical professionals. For specific medical advice relating to your own health, see your doctor.
The KiwiCover BMI Calculator calculates your BMI based on your inputs, but it is not intended to provide an indication of your personal mortality or morbidity risks.