Researchers Say Waist-to-Hip Ratio Should Replace BMI—Here’s Why

Body mass index (BMI) is a controversial weight and health metric, but experts have yet to agree on an alternative. Now, a new study suggests that a person’s waist-to-hip ratio might be a better metric for measuring health as it relates to weight.

For the study, which was recently presented at the European Association for the Study of Diabetes, researchers at University College Cork in Ireland and McMaster University, Queen’s University, and the University of Toronto in Canada drew on data from more than 380,000 adults in the UK Biobank, a large biomedical database and research resource.

A major finding: Waist-to-hip ratio was a stronger predictor of death from any cause than BMI—the standard way of measuring obesity. Each 1-unit increase in waist-to-hip ratio was linked to double the odds of death than the same increase in BMI.

The researchers analyzed data from about 25,000 men and women who had provided their health information up until their deaths. The participants were randomly matched to a group of controls who were of the same age and sex.

The researchers looked to see if the participants had genes linked to obesity, as well as their body measurements, including their BMIs and waist-to-hip ratios.

The participants with a low waist-to-hip ratio were less likely to die early than people with higher ratios. As a person’s waist-to-hip ratio increased, their risk for early death increased. The link was stronger in men than in women.

What’s Wrong With BMI?

BMI is a measure of body fat that’s based on a person’s height and weight. It’s widely used to determine if a person is underweight, normal weight, overweight, or has obesity.

While it’s commonly used by healthcare professionals, researchers, and patients, BMI has a lot of limitations.

“BMI can’t differentiate fat mass from lean mass, or subcutaneous (good fat) from visceral fat (bad fat),” Irfan Khan, a medical student at the College of Medicine and Health, University College Cork in Ireland, told Verywell.

Kunal Shah, MD, assistant professor in the division of endocrinology at Rutgers Robert Wood Johnson Medical School, gave Verywell an example of BMI’s limitations: “A football player may have a body fat percentage of less than 12% but may have a BMI in the ‘obese’ range because [BMI] cannot differentiate between muscle and fat.”

Fatima Cody Stanford, MD, MPH, an obesity medicine physician and associate professor of medicine and pediatrics at Massachusetts General Hospital and Harvard Medical School, agrees that BMI is a flawed metric.

“BMI is not a good measure of health in and of itself,” said Stanford. “There are a variety of factors that one must consider to determine if they have a healthy weight.”

For example, Stanford said that when they’re working with patients, providers “must evaluate the weight itself, and we must do a thorough analysis of their metabolic health to include, but not limited to, fasting blood sugar, cholesterol, and liver function.”

Shah added that BMI also does not account for racial differences.

“BMI has been shown to overstate risk in Black individuals but understates risks in Asians,” she said.

Why Use Waist-to-Hip Ratio?

Waist-to-hip has increasingly been used in the obesity medicine field to calculate a person’s health risk.

According to Khan, the cut-offs for unhealthy ratios are greater than or equal to 0.95 or 1 for males and greater than or equal to 0.8 to 0.85 for females.

Stanford said that a person’s waist-to-hip ratio is by far a better tool to use than BMI as it considers the area where fat is most likely to be problematic—the waist.

“When we carry adipose (body fat) in our midsection, it increases our risk for cardiometabolic diseases like heart disease and type 2 diabetes,” Stanford said.

During the study, Khan said the researchers noted that waist-to-hip is a more consistent measure of fat and, as a result, a better predictor of early death.

“With BMI, the issue is that depending on your individual body composition—i.e. fat distribution—you might benefit from a higher or lower BMI,” said Khan. “That’s not the case with waist-to-hip ratio.”

Khan said their study “demonstrates that a lower waist-to-hip ratio will result in a lower mortality risk, without any nuance.”

How to Tell If Your Weight Supports Your Health

Khan said that the study’s findings do not confirm the replacement of BMI with waist-to-hip ratio just yet.

“However, I would ask those curious to check their general weight and height, BMI, and then their waist circumference and hip circumference to calculate their waist-to-hip ratio,” Khan said.

As Shah pointed out, there are “a lot of measurements out there and a lot of tools out there.”

But how will you know what to do with the information you get? What does it mean to be at a healthy weight?

According to Shah, experts would consider your weight to be health-supporting if your “metabolic risks—[the] risk of diabetes, high blood pressure, risk of heart or stroke—are in line with the general population.”

While Shah said that BMI and waist-to-hip ratio “are a good start” for determining if you’re at a healthy weight, “it’s always helpful to keep an eye on and track these measurements.”

If you’re concerned about your weight, Shah recommends talking to your provider about what you can do, as “there are a ton of strategies and support out there to get you to a weight that will have you feeling your best.”