Harding a freelance writer says that "A lot of people are just freaking out over absolutely nothing," said, "when they're healthier than they think they are."

A lot of people hear overweight and think 'fat person', where you look at these pictures of people in the overweight range and they look perfectly normal," Harding said. "

In the 1980s, doctors began to use BMI as an individual health metric for determining if a person was of normal weight or overweight, but that use of BMI has several limitations.

Harding pointed to the classic example of the athlete with a lot of muscle and a low body fat percentage who has a BMI in the overweight range. The measurement also doesn't account for frame size, bone density, age or ethnicity, she said.

As well, BMI and cardiovascular health have a J-shaped relationship, de Lemos said, where the best body mass index isn't the lowest.

Those with BMIs under 23 actually show a slightly higher risk of heart disease, probably related to other illnesses associated with bad heart outcomes that reduce body and muscle mass.

"People who are normal or even slightly overweight might be even better from a cardiovascular standpoint," he said. The risk then increases again as weight relative to height increases.

Body mass index does have some value outside of clinical settings, de Lemos said, because it allows people to track changes in body mass over time. However, there are other measurements that more accurately indicate health risk, he said.