If your doctor has ever hounded you about a high body mass index (BMI) level, you may have a reason to seek a second opinion. According to a report from Minnesota Daily, a recent study suggests that using BMI to gauge overall health and fitness may not be the best method. Researchers say there are much more accurate measures for determining how healthy a person really is.

The study comes after a growing trend of employers using BMI to monitor their employee’s health for the purpose of determining health insurance costs. As outlined in the Affordable Care Act, employers can charge workers with a high BMI (suggesting poor health) as much as 30 percent of their healthcare costs.

A BMI is a proportional measure comparing a person’s weight and height. The measure, however, fails to distinguish between body parts of different densities, and thus could provide an inaccurate measure of a person’s overall health, depending on factors like the relative levels of bone, muscle, fat, and water mass as a part of a person’s total weight.

The study, carried out by researchers at the University of California – Los Angeles, found that as many as 54 million Americans may have been wrongly classified as unhealthy. Furthermore, they estimated that 20.7 million people with a “normal” BMI level were actually unhealthy.

Because BMI doesn’t take into account other factors that contribute to weight loss, like exercise or diet, it shouldn’t be taken seriously as a true signifier of a person’s health. With such a wide margin of error, BMI begins to seem like a rather arbitrary calculation when determining how healthy a person is.

The authors argued that it is unethical to use such an inaccurate method to determine a person’s overall health, especially when it could lead to unjust charges on their health insurance bills.

A UCLA press release describing the details of the study can be found here.