Is the BMI Chart Actually Accurate?

One of the first pieces of literature a patient receives when walking into our Weight Management department is a BMI (body mass index) chart.  Over the years I have observed hundreds of patients and their facial expressions while they locate their own BMI number.  Once the patient realizes just what the chart is saying, those facial expressions usually morph into some blend of curiosity, frustration, and a where-did-they-get-this-bogus-information grimace.  Not long ago I had an overweight gentlemen look up at me from his BMI chart which he had just received, and in an agitated tone said, “this says I’m extremely obese” – I think he wanted me to tell him that he was fine and the chart was wrong…  Either way, honest discussions about weight, and BMI are difficult.  They are even more difficult if we prematurely dismiss the BMI, as many do, as ancient and outdated guesswork.  While it is true that the BMI does not take into account one’s actual body composition, that does not mean it is an ineffective tool for assessing one’s health as it relates to weight.  The BMI scale has been popular for decades due to its simplicity, ease, and approximation to percent body fat.  However, it seems that the more overweight we get as a nation, the more suspect we are of this scale’s value.  According to a recently published study in BMC Obesity, the naysayers may actually be right, except not the way they were hoping.

About 3000 subjects, males, and females, were recruited to compare participants’ BMI to their actual percentage of body fat.  The goal was to see if these two methods were placing people in the same health-risk category (overweight, obese, etc.).  What they found was that the BMI scale ranked an alarming number of women and men as being in a healthier category than what their actual percent body fat showed.  The authors write:

“19.9% of women and 46.1% men with high %BF were overlooked as being obese according to BMI criteria. The BMI might underestimate [fat levels]…Results from our study support the contention that BMI underestimates [fat levels] in elderly men (aged 70 years and older). Paradoxically, our study also suggests that the BMI markedly underestimated adiposity in young men (aged 20–29 years). It seems likely that for this group, body fat contributes more, and lean tissue less, to body weight than in other groups. While the reasons for this remain unclear, we might speculate that the fat-to-lean tissue mass ratio is disproportionately high as a result of unhealthy lifestyle choices including sedentary behavior and poor nutrition.”

Don’t miss that.  1 out of 5 females, and almost half of the males in this study were in reality ‘obese’, but according to the BMI scale, they were not.  While not without its shortcomings, this study is one more piece of evidence that the true state of affairs might be worse than previously thought.  Thankfully the authors correctly attribute this to our own personal lifestyle choices, rather than some mysterious forces at work.  The good news is that we can change our choices!

The BMI stands as an important tool to categorize health risks based on a person’s weight.  Regardless of its limitations, and it has some obvious ones, it’s not going away.  Its widespread use, ease and yes, even accuracy are invaluable to healthcare professionals.  And unless someone is clearly muscle-bound, it is typically an accurate scale to use.  If anything, we now have good reason to believe that, rather than the BMI boogie man being out to get us, it may be helping some of us seem healthier than we actually are.

There are a variety of ways to get a more exact picture of one’s body composition (such as the non-invasive analyzers we have at Weight Management), but if those are not available, the BMI is a great place to start

For more information on the services and programs offered by CHI Health Weight Management, including how you can use our state-of-the-art body composition analyzers, please call (402) 572-2333