They set out to test which of three metrics—WHR, BMI, or another metric called fat mass index (FMI)—had the “strongest and most consistent association with mortality.”

BMI vs. Waist-to-Hip Ratio

Researchers analyzed data from nearly 400,000 people with an average age of 60. The information came from the UK Biobank, a medical research database containing anonymous health information for half a million people in the United Kingdom. 

The scientists employed a method called Mendelian randomization to consider obesity-associated genetic variants during their analysis. 

They determined the ideal marker of adiposity, or stored body fat, should be strongly, causally, and consistently associated with health outcomes.

The researchers found that WHR had the strongest and most consistent association with all-cause and cause-specific mortality. This association was strongest in men.

They also found a “potentially causal” relationship between WHR and death.

“As prior research used mortality as the health outcome of interest, we did the same,” said Paré. “What we found is that WHR comes out first on all three criteria,” he says. In other words, they concluded that WHR is a better health outcome indicator than BMI.

Paré said the study’s findings support the increasing body of literature showing WHR’s superiority to BMI.

Is BMI a Good Indicator of Health?

Paré thinks it’s time to retire BMI. “There is an emerging consensus WHR is the better marker of adiposity,” he said. “BMI doesn’t take into account body composition, and also tends to exaggerate thinness in short people and fatness in tall people.”

According to the National Heart, Lung, and Blood Institute, BMI may overestimate body fat in athletes and others with a muscular build and similarly underestimate body fat in older people and others who have lost muscle.  

“Another limitation of BMI charts is that they actually tend to underestimate how overweight people are compared to other methods like measuring body fat percentage,” he said.

Matthews pointed to previous research that found half of people considered within average weight or “overweight” according to BMI were found to be clinically obese based on their actual body fat percentage.

“BMI actually paints a rosier picture of people’s health than many realize,” he said.

Paré noted that switching to WHR may be difficult since “BMI is deeply ingrained into clinical practice.” It’s used to determine eligibility for bariatric surgery and also plays a role in diagnosing certain eating disorders.

“It wouldn’t be trivial to switch to WHR,” he said.

Glatt said that BMI can still be a valuable indicator of health, but not in isolation. “Other demographics and biomarkers should be present when making inferences about someone’s general health,” he said.

How to Calculate Waist-to-Hip Ratio

“WHR is easy to measure, and there are excellent videos out there to illustrate,” said Paré.

He said commonly used guidelines say that a WHR of less than 0.95 in men and less than 0.80 in women means you are at a lower risk of developing health issues such as heart disease. Still, the criteria may need adjustments to factor in race and ethnicity, he said. 

To measure your WHR, the National Heart, Lung, and Blood Institute recommends standing up and using a tape measure.

Measure your waist circumference by wrapping the tape measure around the narrowest point of the torso, said Matthews. That point is generally about halfway between the lowest rib and the tip of the hip bone.

Then he said to place the tape measure parallel to the floor and measure the widest point around your buttocks and thighs.

Divide your waist circumference by your hip circumference to get your final measurement. 

According to experts, you can avoid common measurement mistakes by:

• Measuring in the correct areas
• Measuring at the same time of day every time you calculate WTH, as measurements can fluctuate throughout the day due to factors such as water intake and sweating
• Laying the tape measure flat against the skin without making it too tight or too loose
• Standing upright and not slouching

Glatt said that WTH should not be used to determine health outcomes on its own, but is just one tool a healthcare professional can use to assess your disease risk.