BMI Has Fallen Out of Favor as a Measurement Tool: Here’s What Nurses Need to Know

• The American Medical Association is moving away from using Body Mass Index as a health measurement.
• The widely used tool has been labeled a poor indicator of accurately assessing a person's weight because it does not account for differences across race/ethnic groups, sexes, genders, and ages.
• The AMA offers alternatives for clinicians diagnosing obesity.

The American Medical Association (AMA) is now recommending against using Body Mass Index (BMI) to measure patients' weight and health.

BMI is widely used to help clinicians assess health risk factors, shape care plans, and even influence public health policies. But the policy change comes after years of studies showing BMI is not an accurate way to diagnose obesity. The calculation alone — weight divided by height squared — is limited and informed by decades of flawed science that some consider discriminatory.

Fortunately, there are alternatives. Here's what nurses need to know about new recommendations and what they can do instead.

BMI: The Problems

BMI was meant to provide a quick equation to measure obesity in the general public. It was created by a Belgian man named Lambert Adolphe Jacques Quetelet almost 200 years ago, with the majority of his subjects being white males. The equation never factored in race, ethnicity, age, or gender.

“BMI [is] an imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders, and age-span,” an AMA statement explained.

BMI is still used to diagnose obesity in children and adolescents. However, the concerns are similar to those identified in adults. Height and level of sexual maturation also affect the relationship between BMI and body fat in children and adolescents.

The U.S. Centers for Disease Control and Prevention (CDC) also has warned against clinicians using BMI solely to determine whether a patient is at a healthy weight. The CDC has recommended other factors to consider, including bone mass, excess fat, and muscle. BMI measures body weight, which includes body fat, bones, muscle, fluid, and other organs. For example, a muscular person or athlete may have a higher BMI due to their muscle mass.

“There are numerous concerns with the way BMI has been used to measure body fat and diagnose obesity, yet some physicians find it to be a helpful measure in certain scenarios,” says AMA Immediate Past President Jack Resneck, Jr., MD, in the statement announcing the policy.

The new policy points out that BMI is better used to measure fat mass for the general public.

BMI: The Alternatives

The AMA recommends clinicians use other measures for diagnosing obesity, including:

• Measurements of visceral fat
• Body adiposity index
• Body composition
• Relative fat mass
• Waist circumference and genetic/metabolic factors

Other methods to determine weight are not readily available to clinicians, including:

• Underwater weighing
• Biometric measurements
• Dual-energy absorptiometry (DXA)

These methods, however, can be expensive and must be performed by specially trained professionals.

The new policy could eventually reach health agencies like the CDC and World Health Organization, both of which recognize the limitations of BMI but still recommend the tool as a way to measure body fat. The AMA noted it would educate doctors on BMI limitations but not discourage them from using the tool. Nursing schools will most likely follow.

School nurses often have the responsibility to report BMI. As of 2013, 25 states required schools to screen students' BMI results, and 11 states mandated schools to report students' BMI to parents in order to lower their risk of pediatric obesity. Studies have shown BMI reporting doesn’t reduce obesity.

As research and practices evolve, the nursing community will be on the front lines of bringing in new tools, especially with the rise of AI in nursing and nursing innovation. These new tools will help clinicians manage patients and their health/weight more effectively and focus more on preventative care.