An Intuitive Eating Dietitian’s Thoughts on BMI

From Kelsey Chadwick, MS RDN

January 26th, 2024

As mentioned in a previous blog post, the formula we use for body mass index (BMI) was invented in the 19th century by a Belgian statistician, Adolphe Quetelet. Quetelet was not a physician and did not study medicine. He created this formula as a quick way of understanding the relationship between height and weight in the “average” person. Keep in mind, his research only looked at European men in his area. Quetelet made it clear that his research was always focused on population averages, and wouldn’t be very useful at an individual level. Unfortunately, we have not heeded this recommendation… so today I’d like to dive a bit deeper into the many flaws of the body mass index.

The BMI suggests that there is a “normal weight” range for everyone based on height. This simply isn’t the case. Genetic and environmental factors certainly influence our body weight and, as mentioned in an earlier blog post, we all have a set point weight range, where our body biologically functions comfortably, and for many people this is outside the “normal” weight range. This means, we have problematized the mere existence of many bodies through the use of BMI.

Another big flaw with using BMI to define health status is how limited the formula actually is. Body mass index simply is weight over height squared. This obviously only takes into account a person's weight and height. It does not measure any other parts of the body like muscle mass, body fat mass, bone mass, or overall body composition. It doesn’t even take into account the differences between men and women. It certainly doesn’t recognize differences in other health markers, like lab values or health history. So using BMI as a “predictor” of health status leaves much to be desired and ignores the natural variations in bodies based on age, sex, genetics, and ethnicity.

Let’s be clear—the use of BMI isn’t just a statistics problem. BMI is used at physical exams and specialist appointments as an opportunity to offer weight loss as a “treatment” and “solution” to various medical conditions like PCOS, diabetes, hypertension, GERD, infertility and many others. It often becomes the focus of medical appointments for anyone not in the “normal” weight category—often leading to feelings of frustration after not receiving the same care that someone in the “normal” weight category would receive. In addition to these flaws, we must also recognize the impact BMI has on diet culture and eating disorders. BMI has done tremendous harm to folks all over the world by othering individuals and perpetuating weight stigma at a systemic level.

There are far more scientific and medically sound methods for health care providers to determine health and treat medical conditions, rather than using BMI. Health should be determined on an individual basis, and as Quetelet warned almost 200 years ago, the BMI formula is not the tool for the job.