Why The Body Mass Index (BMI) Is Bullshit

Anyone with muscle will tell you that the popular health screening test, the Body Mass Index (BMI), is bullshit. I have muscular thighs and a firm butt that fills out my jeans — and those muscles can also deadlift, run, and squat like a boss. My body isn't perfect (I love my mac and cheese), but my health numbers (cholesterol, blood pressure, awesomeness) are consistently better than average. I’m fit, I'm strong, and I exercise daily; yet, by BMI standards, I’m overweight.

The National Institute of Health says that your BMI is a measure of body fat based on height and weight. The formula is [your weight (in pounds) divided by your height (in inches)²] x 703. It’s not designed to be used as the determining factor of your health, but it’s so easily measured that some companies offer financial incentives for employees with a "healthy" BMI reading. My problem is that the test isn’t appropriate for everyone; it overestimates body fat for muscular builds, and underestimates body fat for older adults who have lost muscle.

The glaring flaw is that your BMI doesn’t differentiate between amounts of fat versus muscle. Think about it: 25 pounds of fat looks a lot different than 25 pounds of muscle around strong, dense bones — and it has an entirely different set of health implications. Carrying excess weight has been linked to chronic health issues such as cardiovascular disease and type-2 diabetes, so understanding your current risk is essential to changing and preventing further complications. But, where your body holds onto fat also makes a big difference — one that BMI doesn’t take into account. Generally, excess visceral fat (the kind stored around your waist) is more dangerous than excess fat elsewhere. So, why do we use BMI at all? Because it’s easy.

I’m not the only one calling BS on BMI. “How can you possibly measure a person’s body fat based on their height and weight alone?” asks fitness expert Neghar Fonooni. “This erroneous measurement has the capability to misinform women of their true body composition, often times encouraging body dysmorphia and body-image issues. The entire measurement is unreliable and should be done away with completely.” Fonooni is healthy, sexy, and fit (case in point here) but she shares that at 5'1" and 135 pounds, her “BMI is considered overweight.”

If you're healthy, your BMI can feel like one big mind game, toying with fragile emotions and lingering self-doubt. For me, there are a lot of reasons why I work out — and, yes, one of them is to look good. I know I’m fit, and I’m getting fitter; I recently set a 10K personal record. But, that doesn't diminish the sting I feel when I plug my height and weight into an online BMI calculator and it tells me I’m overweight. I work hard, and I want every number to reflect that effort. What I don’t want is an oversimplified number that tells me I’m unhealthy without accounting for the measurements that really matter.

On the other end of the spectrum, being told your BMI falls within the normal range can provide a false sense of security. If your BMI is "healthy," you're healthy, right? Not if you don’t take other important lifestyle factors and health stats (cholesterol, blood pressure, bone density, etc.) into account.

The sentiments behind measuring your BMI are well-intentioned; it’s important to constantly check in with your health. But, the practical applications of the index are misguided. There are plenty of health tests we’ve improved upon as our understanding of the human body progresses — and there are lots of other gauges of health that medical and fitness professionals are starting to stress. For example, a new test, called A Body Shape Index (ABSI) takes waist circumference, height, and weight measurements into account, and was found to be a better predictor of premature death than BMI, according to findings reported in PLOS ONE.

“Although it is new to the fitness scene, the ABSI may be an important way to measure one’s health,” explains exercise physiologist with the American Council on Exercise Jacque Ratliff, MS, CSCS. “The original BMI formula only took into account the height and weight of a person, which left out a major component in health — body composition.”

According to Ratliff, some risky numbers that we (especially women) should be watching out for include a waist circumference of greater than 35 inches and a total body-fat percentage of 32% or higher. Of course, there’s no single measurement of good health — but the BMI test has been judging me for years, and I'm done with it.