Height and weight are the two factors that determine a person’s body mass index (BMI), a measure of body fat and general health. However, this one-size-fits-all approach may be flawed, according to researchers from the University of California, Los Angeles (UCLA). Published in the  International Journal of Obesity, their study reveals how ineffective BMI is, as well as the number of people who may be inaccurately deemed overweight or obese. Doctors and patients may have to turn to alternative methods to accurately assess healthy weight ranges.

BMI is a calculation that divides people into one of four categories: People who are underweight, with a score of less than 18.5; normal weight, with a score between 18.5 and 24.9; overweight, with a score of 25 to 25.9; and obese, with a score of 30 or greater. Basing this calculation on height and weight alone, however, doesn’t take into account a person’s bone, muscle, or fat proportions. For example, a person with exceptional muscle tone and low fat is more likely to have a higher BMI compared to someone with higher fat and lower muscle tone — this happens because muscle is four times as dense as fat tissue. In fact, many professional football players’ BMIs would place them in the obese category when they’re actually in better shape than the average person.

Worldwide obesity rates have more than doubled since 1980 and, according to the World Health Organization, most of the world’s population live in countries where being overweight or obese has a higher risk of death than being underweight. With obesity being such a public health concern, measuring it correctly becomes even more important.

Nearly half of those whose BMIs labeled them as overweight were actually healthy, according to data on their other health measures. Fifteen percent of those who were classified as obese were also considered healthy. And when the researchers looked at participants classified as healthy, they found 30 percent were actually unhealthy when their health measures were taken into consideration. If the findings were extrapolated to the entire American population, the researchers said as many as 54 million people are incorrectly told they’re unhealthy.

According to the  National Academy of Sports Medicine, BMI first appeared in the medical world in the mid-1800s. However, the measurement didn’t become an omnipresent health measurement until the  National Institutes of Health approved BMI as a standard health measurement in 1998. This action led an additional 30 million Americans to be moved from a healthy-weight category to an overweight one.

It’s not uncommon for U.S. companies to consider their employees’ BMIs when determining how much they’ll pay for health care. But if the  Equal Employment Opportunity Commission adopts a new rule set to be proposed in April, then anyone with a high BMI would be required to pay a higher health insurance premium to cover the medical costs associated with obesity.

"There are healthy people who could be penalized based on a faulty health measure,” said the study's lead author A. Janet Tomiyama, the director of UCLA's Dieting, Stress and Health Laboratory, in a press release, “While the unhealthy people of normal weight will fly under the radar and won't get charged more for their health insurance. Employers, policy makers and insurance companies should focus on actual health markers."

However, if the BMI scale is eventually deemed as an ineffective tool to measure weight and health risks because of questionable accuracy, there are other avenues for assessment. There are many methods to measure body composition ranging from simple, at-home techniques to complex procedures. If you’re thinking of opting out of relying on the potentially faulty BMI scale, here are some alternative modes of measurement to see what works for you.

Skin Calipers 

This inexpensive plier-shaped tool can be used to clamp sections of fat off of the body and measure body composition accurately, and within just a few minutes. A skin-fold assessment can be done using three, four, or seven different parts of the body, such as the chest, arms, abdominals, thighs, and back. However, accuracy is completely dependent upon the experience and knowledge of the technician measuring you.

Tape Measure

To be considered healthy, waist circumference should be less than half of your height. For example, if you are a 5-foot (60 inches) tall female, your waist circumference should be 30 inches or smaller. According to the Centers for Disease Control and Prevention, excessive abdominal fat may put you at greater risk for developing type 2 diabetes, high blood pressure, and coronary heart disease. To measure, stand straight and place the tape measure around your mid-section just above your hip bones along the belly button. Relax, do not suck in your gut, and do not compress the tape tightly around the waist.

Hydrostatic Weighing

You’ll need a bathing suit for this form of measurement. Hydrostatic weighing, more commonly called underwater displacement weighing, compares a patient’s normal body weight outside of the water to their bodyweight while completely submerged. Doctors use the two numbers, along with the density of water, to calculate the patient’s density, which ultimately serves as an estimate of their body composition. It is one of the most accurate assessments with a very small margin of error, making it the go-to standard for clinical research settings.

Air Displacement Plethysmography

This method of measurement follows the same technique as underwater displacement weighing. Patients sit in a small, pod-like machine and technicians measure how much air was displaced or pushed out of the machine by the patient’s body. Using the measurement of air before and after the patient entered the pod along with the density of air, technicians are able to calculate their body composition. The machine is usually found in high-level training facilities and is considered one of the most accurate measurements of body composition.

Bioelectrical Impedance Scale

This scale is equipped with electrodes under each foot, which shoot tiny electrical impulses up throughout the body, and measures how quickly those impulses return to the device. Lean tissue conducts electrical impulses faster than fatty tissue, allowing the device to measure fat composition by the speed of the impulses return. The faster the response time, the leaner the physique.

Dual Energy X-Ray Absorptiometry

This scan emits high and low energy levels of x-ray beams into patients as they lay on a table one body part at a time.  It measures bone mineral density, lean body mass, and fat mass. Technicians can provide an accurate breakdown of the body composition level for each section of the body.

Source: Tomiyama AJ, Hunger JM, Nguyen-Cuu J, and Wells C. Misclassification of cardiometabolic health when using body mass index categories in NHANES 2005-2012. International Journal of Obesity.  2016.