BMI or BS?


Every time I visit my doctor for my annual checkup I receive an official body mass index (BMI) that is documented in my files. I’m pretty sure you do too. But what exactly does BMI mean and what does it measure? Should we blindly trust BMI because doctors use it on both children and adults? Let’s take a closer look.

The Origin of BMI
The formula behind body mass index was developed by Belgian mathematician Adolphe Quetelet in the mid-nineteenth century as part of his research in an area he called “social physics:” the application of statistics to social science. Quetelet was fascinated with using data to quantify social behaviors across a variety of areas, measuring everything from marriage rates to crime rates. He segmented data using statistical curves to determine if something – or someone – was “normal,” below average, and so forth. We do this so much today that it’s hard to believe it carried the fancy name of “social physics” back in the day.

In 1972, the term “BMI” was coined by Ancel Keys in The Journal of Chronic Diseases as a mechanism to quantify weight in proportion to height. Our BMI is calculated by taking our weight in pounds, multiplying it by our height in inches squared, and, finally, multiplying that result by 703. Go ahead… calculate yours now. You can use a calculator if you’d like.

Implications of BMI Scores
A BMI below 18.5 indicates that we are “underweight,” a score between 18.5 and 24.9 is said to be “ideal weight,” 25.0 to 29.9 is considered “overweight,” and a score of 30.0 and above is viewed as “obese.” In a sense, BMI is a Cliff’s Notes version of our body’s health. It’s an attempt to boil down our relative level of “in-shapeness” to a simple number. If my BMI is 17, I should eat a burger… if it’s 32, I should stop eating burgers. Simple, right?

Trouble with Math
Quetelet was a brilliant mathematician, yet he was not an expert in the field of health. And, in his defense, he could not have anticipated the major health developments that have occurred since his original research. Watch nearly any of the Olympics events and you’re likely to see athletes that would fall into each of the BMI categories that don’t really belong there.

Wait… Weight?
We can certainly make the argument that weight may not be the metric to use to give us a sense of how thin or thick we are. Waist size or ratio between parts of our body can demonstrate fitness. Our waistline is one of the clearest physical signs of obesity. Muscle weighs more than fat, so many athletes find themselves in an obese BMI category which certainly doesn’t seem right. But, we don’t have to be athletes for BMI to over-penalize us. According to the World Health Organization, nearly half of those with overweight BMIs are perfectly healthy based on more detailed and thorough health measurements.

Error Prone
The majority of the U.S. population leads a sedentary lifestyle. Obesity rates are on the rise. So, clearly there is a need for us and our doctors to determine if we are obese and for us to adjust our lifestyles accordingly. BMI, however, leads to a lot of false positives. And these false positives have real implications. Some insurance companies charge a higher premium based on one’s BMI. So, fit individuals may be paying a higher price due to an inaccurate formula used by doctors. We could be faced with a monetary punishment for a faulty scoring system. Yes, it’s a system accepted by NIH and many other well respected organizations, but it’s highly inaccurate.

BMI is a simple formula that doesn’t account for many important factors which are strong indicators of one’s health status. Superior alternatives are not necessarily costly, but they require more than a quick math calculation. A skin fold assessment, used by a skilled technician with skin calipers, measures the amount of fat on fewer than 10 areas of the body to determine body health. No caliper? No skilled technician? Another option is simply to use a tape measure to determine your waist circumference at the belly button, and, if it’s less than half your height you are in the “healthy” category. There are more costly and complex options involving water displacement and even x-rays, but these are not necessary to get a good sense of your overall body health.

We’d love to hear from you. What alternative to BMI do you think is most accurate and feasible? Comment below or on our Facebook page or tweet us at @flytefitness.

Be Flyte Fit,

Taylor Hahn
Contributing Writer, Flyte Fitness
Certified Group Fitness Instructor & Personal Trainer