Study: Waist-to-hip ratio should replace BMI to measure healthy weight

Measuring waist-to-hip ratio, not body mass index is a better indicator of healthy weight -- and may better predict early death, a new study says. Photo by PublicDomainPictures/Pixabay
Measuring waist-to-hip ratio, not body mass index is a better indicator of healthy weight -- and may better predict early death, a new study says. Photo by PublicDomainPictures/Pixabay

Sept. 21 (UPI) -- New research suggests that waist-to-hip ratio, and not body mass index is a better measure of healthy weight -- and may predict early death better than BMI.

The researchers urge using the new method to replace BMI, which the Centers for Disease Control and Prevention has called "an inexpensive and easy tool" because that calculation requires only a person's height and weight.


But researchers said the waist-to-hip ratio also is a "quick and easy measurement," calculated by dividing waist circumference by hip circumference.

Their work is being presented this week at the annual meeting of the European Association for the Study of Diabetes in Stockholm.

BMI is calculated by taking a person's weight in kilograms and dividing by the square of height in meters, with a BMI of 18.5 to 24.9 considered healthy. But this measurement doesn't take into account fat distribution, the researchers said.


"It doesn't consider where fat is stored -- whether it's accumulated around the hips or the waist. As a result, BMI doesn't reliably predict risk of disease or mortality," said Irfan Khan, a medical student at University College Cork's College of Medicine and Health in Cork, Ireland, who carried out the research with colleagues in Canada.

This means that a person who has accumulated fat around the waist will have the same BMI as someone of the same age and height who stores their fat around the hips, despite the health risks of abdominal fat, the researchers said.

Khan said waist-to-hip ratio better reflects levels of abdominal fat, including visceral fat, which wraps around the organs deep inside the body and heightens the risk of a range of medical conditions.

More accurate measurement of a healthy body shape "may make a significant difference to the ill health and deaths caused by type 2 diabetes, heart disease, some cancers and numerous other conditions," he said.

According to Khan, the message is simple: the lower a person's waist-to-hip ratio is, the lower the mortality risk.

Waist-to-hip ratio is "a stronger and more robust measure" compared to BMI, he told UPI in an email.


"Instead of aiming for a specific BMI target, which may or may not be beneficial depending on your individual body composition, aiming for a lower [waist-to-hip ratio] will always lead to a lower mortality rate," he said.

Starting out, the researchers wanted to determine whether waist-to-hip ratio, or fat mass index, would more reliably predict mortality across different fat distributions.

The fat mass index is calculated by dividing fat weight in kilograms by height in meters squared; BMI considers a person's total weight in the measurement.

First the study's investigators analyzed data of U.K. Biobank participants who had genes known to predispose them to weight gain and obesity. Their analysis indicated that higher levels of fat caused increased mortality, rather than being merely correlated with it, the release said.

Next, they applied information on the genes associated with the three measurements -- BMI, waist-to-hip ratio and fat mass index -- to data on roughly 25,000 White men and women whose health had been tracked as part of the UK Biobank study until their deaths, and a similar number of "age, sex, and genetic ancestry-matched" controls.

Despite using genetically determined waist-to-hip ratio for their analysis, the scientists said their findings apply equally to conventional measurement of waist and hips.


The researchers found that the risk of an early death was lowest for those with the lowest waist-to-hip ratio and then steadily increased with rising waist-to-hip ratio.

By contrast, individuals with either an extremely high or low BMI or fat mass index had an increased risk of death compared to those with a moderate BMI or fat mass index.

For example, each one-unit increase in waist-to-hip ratio increased the odds of an early death by almost twice as much as a one unit increase in BMI or fat mass index.

The scientists also discovered waist-to-hip ratio was more strongly associated with death from all causes than BMI or fat mass index. This link was stronger in men than women.

According to Khan, clinicians may already have a tape measure on them for certain examinations: such as measuring a patient's apparent versus actual limb length or measuring the liver's span during abdominal or gastrointestinal exams.

"Waist and hip circumference is easy to measure in adults using the tape measure, so I don't see why doctors shouldn't carry around a tape measure to do this as well," he said.

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