The Problem With BMI

It’s human nature to want nice, neat numbers to describe ourselves and our bodies accurately. First, we thought that the scale gave that to us, but we know now that our scales are actually quite faulty. After that, we turned to BMI, or Body Mass Index. But is BMI really more accurate?

BMI was founded by a man named Adolphe Quetelet back in the 1830s. Quetelet was a Belgian mathematician, statistician, and astronomer; not an expert in biology of any sort. Quetelet’s motive to creating BMI was a bit odd: He made it to help insurance agencies determine an individual’s risk of falling into poor health. He did this as a favor for Louis I. Dublin, the vice president of the Metropolitan Life Insurance Company, who was looking for a quick, easy way to sort people according to their apparent risk. (Quetelet also expressed an interest in the “perfect proportions of the average man,” a phrase that should set off a few alarms in your head.) His solution was simple, easy, and only required two pieces of information. The equation for BMI is [weight]/[height]^2. Your individual number lands you somewhere between 1 and 100, which supposedly tells you how healthy you are:

The CDC and NIH both promote BMI as the most accurate existing form of judging our health, but many experts disagree.

  • BMI is more likely to classify you as “underweight” if you are short and “overweight” if you are tall. If you are short and overweight, the equation cuts your height by a drastic amount and is more likely to give you a lower BMI. If you are tall, your weight may not cut your height by nearly enough.
  • BMI does not account for muscle mass. If you are a very muscular person, your weight is likely to be a little higher. Muscle weighs more than fat, after all. An olympic weightlifter who weighs 250 and stands at 5’10” is going to have the same BMI as everyone else who shares those measurements.
  • BMI does not account for genetics, activity, age, or any other factors. There’s more that goes into our personal fitness than just our height and weight, and BMI factors in none of them.

So, are there any better options?

If the scale and BMI both don’t work, is there anything we can use to quantify our health?

Personally, I would recommend staying away from measurement systems that rely too heavily on equations and systems that are designed to suit everyone. There are just too many different factors involved in our health for us to try putting ourselves into one of a few classes. Instead, I would recommend tracking body measurements (i.e. waist, hips, chest, arms, thighs) and using progress photos as a way of comparing yourself to yourself! Or, if you want to track your performance, keep a record of your mile-run times, how many push-ups you can do in a minute, and similar exercises. Maintaining an ongoing fitness journal will let you know how your body is changing more accurately than a mathematical equation.

However, there have also been some attempts to correct the faulty BMI system. For instances, many experts suggest that a waist-to-height ratio is more telling than weight-to-height because an excessive amount of fat in the waist area puts stress on the inner organs. Dr. Margaret Ashwell, former science director of the British Nutrition Foundation, recommends this as a general guideline. Although she admits that it’s a little faulty because fat can distribute to many parts of the body, waist-to-height can still be used to determine the risk for specific diseases like type 2 diabetes and cardiovascular diseases. To calculate your ratio, you can enter your measurements right here.

Others have tried to correct Quetelet’s equation by adding onto it, such as the ABSI equation. This equation attempts to get rid of the bias that gives shorter people a lower BMI and taller people a higher BMI, so if you’re an average height, you may not see a major difference at all. This system also includes some body measurements, so whip out that tape measure if you want to give it a shot! Check it out right here. Once you get your results, you’ll see that it calculates your normal BMI and then gives you your “New BMI,” shown in the column to the far right:

I still find this equation a bit problematic because it only addresses one of many problems with BMI, but it’s very interesting to see how your number changes after the tall-fat/short-thin bias is eliminated.

My best recommendation is actually this equation from Very Well Fitness, which you can find here. I actually found it while I was searching for how much protein I should be eating, not for a BMI replacement, but it gave me some interesting information. It uses body measurements to come up with a body fat percentage for you and then walks you through the math of determining how many pounds of fat are on you. I’ll use myself as an example: After entering my measurements, it stated that 11% of my body is fat. After that, I multiplied by body weight by that percentage (132 x 11%) to discover that I have 14.5 lbs of fat on me. This means that my lean body weight, aka my body weight without any fat, is 117.5. I don’t know what math is behind the calculator on the site so I can’t speak to its accuracy, but it was more insightful than the other equations I’ve tried.

Still, I’m a huge proponent of only comparing yourself to yourself, so I would still rely more on bodily measurements, progress photos, and fitness tests to track your improvement. Don’t worry so much about systems that place you in a category where you have to measure up to an “average.”

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