Correction: An earlier version of this story misquoted Sandra Adamson Fryhofer in her characterization of a study on body fat and mortality rates. She said a person with a high body-fat percentage can be at risk even “if what you weigh is fine,” not if you are “only mildly overweight.” This version has been corrected.

(A new study says that the numbers on a scale aren’t a good way to determine a person’s health.)

A new study is taking aim at one of the most commonly used standards for assessing health.

BMI (body mass index), which measures a person’s height in relation to weight, fails to capture a true picture of health, according to a new study released the by Annals of Internal Medicine, and is incomplete as a method of determining risk factors for heart disease, diabetes and other chronic conditions.

The study, which focused on men and women age 40 and older, found that a person’s mortality risk is increased by a higher body-fat percentage — independent of BMI. In other words, the numbers on a scale are not an adequate method for determining a person’s health because they don’t take into account whole-body composition (muscle, bone and fat).

“This is a wake-up call,” says Sandra Adamson Fryhofer, past president of the American College of Physicians and an internist in Atlanta, explaining that it shows person with a high body-fat percentage can be at risk even “if what you weigh is fine.”

“It’s telling us that we need to do more than simply watch our caloric intake,” she says.

For decades we’ve equated lower weight with better health and often pegged weight-loss goals to the standardized BMI ranges, which don’t take into account how they are achieved (underweight: less than 18.5; ideal weight: 18.5-24.9; overweight: 25-29.9; obese: 30 or greater). In other words: Using the current system, numbers trump lifestyle.

“The BMI doesn’t take into account that a person can be lean due to unhealthy behaviors, including extreme dieting or drug addiction,” explains James Fell, a fitness writer and author of “Lose It Right: A Brutally Honest 3-Stage Program to Help You Get Fit and Lose Weight Without Losing Your Mind.” And although that person might achieve a BMI within the ideal range, or a low number on the scale, it’s certainly not healthy or a formula for longevity. In fact, Fell argues that, in that scenario, it can actually be better to be slightly overweight and living a healthy lifestyle than to have the “right” BMI and weight but achieve them through extreme measures.

Another problem with BMI: It can be skewed by muscle mass. “The BMI is far from a perfect tool because it doesn’t differentiate between the person who has a spare tire around their waist from a person who is large because of lean muscle,” says William D. Leslie, a professor of medicine and radiology at the University of Manitoba.

That is why he says a new standard that takes into account total body composition — fat, muscle and bone — is necessary.

This shift in perception is also being echoed by the body-acceptance movement that has gained increased pop-culture visibility over the past year. “We’re moving out of the era where we thought we could look at a person and determine if they are healthy,” Fell says. And that is leading to an expanded definition of beauty. In February, the Sports Illustrated Swimsuit Issue featured a plus-size model, Ashley Graham, on its cover and touted her as a symbol of an era of beauty that is no longer one-size-fits-all. Similarly in January, Aerie (American Eagle’s lingerie brand) debuted a campaign featuring plus-size model Barbie Ferreira, whom Jen Foyle, global brand president for Aerie, calls “strong and beautiful.”

But just because the guidelines are changing does not mean that we can forget all that we know about the dangers of excess fat, which has been linked to increased risk for cardiovascular disease and Type 2 diabetes. In women, it also is associated with breast cancer. “Nonessential fat does pose medical risks,” explains Andrew Jagim, assistant professor of exercise and sport science at the University of Wisconsin at La Crosse. “So we can’t applaud a rationale that ignores it.”

Ultimately, however, we’re moving into an era where experts are realizing that behaviors matter as much as numbers when it comes to body size and health — and that body composition is a better determinant of health than standardized numbers. “Optimal health is becoming more about personal sustainability and best practices,” Fell says. “Because if you exercise and eat well, and don’t drink too much or smoke, you’re going to be better off than if you push hard to reach a number on a scale or a target BMI range.”