A person's body mass index (BMI) is not indicative of their health status. New research shows that those within a 'healthy' BMI range were not so healthy after all.

The BMI formula works by measuring a person's weight and dividing it by their height. It reportedly works to calculate the fat in the body. The result will indicate the corresponding "weight status," which dictates that an individual is either underweight, normal weight, overweight or obese.

However, research posted in the journal Annals of Internal Medicine found that many people who fell within the "healthy" weight spectrum had the tendency to die of any cause.

Fitness VS Fatness

While the BMI can calculate the weight of the person, it doesn't tell how much fat his or her body has. Two people could have the same weight but some people could have more muscle than fat, while some may have more fat than muscle.

"BMI is useful, but increasingly we're seeing it has limitations," said lead author Dr. William Leslie of the University of Manitoba in Canada, via Time. "Our study highlights some of the nuances around the assessment of body composition that tells us that BMI can lead us astray in some situations."

For their study, Leslie and colleagues looked at nearly 55,000 middle-aged Canadian adults. The participants were followed for seven years, US News & World Report noted. Their bone scans were also taken to measure the density.

They found that men and women with large amounts of body fat were more likely to die over the next couple of years. In the study, they found that men with the highest body fat (36%) were nearly 60 percent likely to die during the course of the study while those with lesser body fat (28%-32%) had a lesser risk.

The same results applied to women. Those with the highest percentage (39% and higher) of body fat were more likely to die during the study period compared to those with 30 to 34 percent body fat.

BMI Measurement for Health is Outdated, Researchers Say

According to Leslie, thin people with excess weight in the middle are in danger of dying from heart disease. Body fat can be more accurately measured with a tape measure to the waistline, UPI reports.

"I'm not saying BMI isn't helpful, clearly it is. But it's a crude measure and body composition is not accurately captured by BMI alone," Leslie said. "To say someone is obese implies that they have too much fat. BMI may misclassify some people as having excess fat, which isn't the case. At the other end of the scale just because you're not in the obese range, doesn't mean you don't have excess fat."

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