The Body Mass Index (BMI) has been widely used as a guide to classify people who are overweight and obese and therefore have a higher risk of various diseases such as stroke, diabetes and heart disease.
People who are over weight or obese have a high risk of disease and early mortality. This has placed a heavy burden on health services and budgets around the world. The BMI is one way Governments and Health Authorities have tried to tackle the obesity epidemic.
The BMI is calculated as weight in kilograms divided by their height in metres squared. However it is a hard index to calculate and understand. The various BMI risk ranges and categories are also hard to understand.
There are many charts and websites to help people calculate their BMI, but the results are hard to relate to the relationship between weight and height.
Recent research has identified a much simpler index, based of measurements of waistline compared with height.
Studies have shown that the waist-to-height ratio was a better predictor of lifespan and the risk of disease and death. It is easier to calculate and understand.
It can be used with any unit of measurement from centimetres to inches, metres to feet.
It is just a simple ratio or waist circumference to body height, and there is no squaring of the height as as is required for the BMI.
This article discusses the new waist-to-height ratio (WHtR) and the evidence that it is better than the BMI and the suggestion that it should replace it.
The general advice is to keep your waist circumference less than half your height in any unit of measurement. This can assist in improving general health and life expectancy for all body shapes and sizes and ethnic groups around the world.
While the BMI was useful and was similarly correlated with general health and mortality risks it did not consider how excess fat was distributed throughout the body. Abdominal fat around the waist, which is indicative of excess fat build up around the liver, heart and kidneys, has been shown to be worse than excess weight on the bottom and hips. Having a large waist size in relation to height increases the risk of diabetes and heart disease and diabetes.
For overweight and obese people the waist-to-height ratio (WHtR) appears to be better predictor of mortality risk than BMI. A study of 300,000 people in Britain, found the (WHtR) was a better predictor of high blood pressure, diabetes and cardiovascular events like strokes and heart attacks than body mass index.
A Taiwanese study, that involved more than 20,000 men and 15,00 women, found that WHtR was significantly better BMI or Waist Circumference in predicting diabetes, hypertension, high total cholesterol, high triglycerides, and low HDL-cholesterol in the people studied.
One way of explaining the extra risk that occurs by being over weight is by calculating the potential average loss years lost at various ages such as 30, 50, and 70 years.
In the simplified charts shown below the explanation for the boundaries and colors is:
Waist-to-height ratio less 0.5 – Low Risk Level. The boundary at a ratio of 0.4 represents low risks for ‘normal’ body shape (green) and potentially slight risks from being underweight for height (brown).
Waist-to-height ratio above 0.5 – Moderate to High Risk Level. The boundary at a ratio of 0.6 represents moderate risks (yellow) and high risks (red).
Some examples for the threshold ratio of 0.5 are:
Because it is much easier to calculate and understand, the Waist-to-Height Ratio (WHtR) would probably be better for individuals and health authorities to use in trying to encourage people to lose weight and understand what extra weight means for their health and life expectancy.