Typically you’ll go to the doctor and when you get your discharge paperwork there can be a list of diagnoses at the end. Or sometimes you’ll go in, get weighed and the first thing your provider mentions as they go over your vitals is, “oh, looks like you’re [overweight, obese] according to your BMI, you should try to lose some weight.”
Well, is that true? And what is BMI anyways?!
The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms and height in metres.
BMI formula was created by a Belgian scientist in the mid 1800s. It was then cited numerous times in a 1972 medical article by Ancel Keys. There had long been sought a metric that could simply distill a person’s height and weight into ranges. Something desired by life insurance companies, and later health insurance, to help adjust the amount people pay for their insurance based upon a single health metric, in this case someone’s “fatness”. Admitted by Keys himself, the BMI metric was only meant to be used for adult men, ages 20-65. How BMI became so pervasive in medical documentation is not entirely clear. However, per CDCs own guidelines to providers, “Because BMI does not measure body fat directly, it should not be used as a diagnostic tool.”
However, far too often, it is used as a diagnostic tool. Sometimes your provider’s medical record will automatically add a diagnosis of “obese” to your chart, based off your BMI.
So, is there any utility to BMI at all? One of the populations that is most inaccurately represented by BMI are athletes or people with significant muscle mass. A waist measurement may be a more superior metric to track, when trying to evaluate a person’s potential risk for diabetes and heart disease. Per American Heart Association and National Heart, Lung, and Blood Institute; waist measurement of >35” for women and >40” for men are correlated with a higher risk for having a heart attack or becoming diabetic. It has been shown that the waist measurement is superior to BMI in predicting risk for developing these serious chronic conditions.
So, why don’t we measure our waists at our primary care? Well, it’s not as simple as getting a height and weight. People are sensitive about exposing their midsection and someone running a measuring tape around your waist is uncomfortable, to say the least. It also takes time to get disrobed appropriately, and then someone has to measure in the right place! Accurate waist measurement should he taken at the navel aka bellybutton. The tape should lay flat and be snug to the skin, but not cutting into your waist. Your abdomen should be relaxed, hopefully you’ve had a chance to pee. Similar to body weight, if you begin to track your waist measurement, you should strive to do it at the same time of day. Usually it is best early in the day, just after waking up and having gone to the bathroom.
Waist measurement gives a more accurate picture of central abdominal fat, which has a strong correlation of fat being around your vital organs. Increased abdominal fat is also associated with increased inflammatory markers and other risks for chronic disease. Other countries focus on waist to hip ratio markers, instead of a unique waist measurement. For instance the World Health Organization promotes using waist to hip ratio: women >0.85 men >0.9. (Ie take your waist measurement and divide it by your hip measurement.) That, however, also has its challenges in that it can be difficult to get a hip measurement in the same place each time. (No belly button landmark!) I found the AHA guidelines of <35” waist for women and <40” waist for men, a metric that, although not perfect, is a good general standard for many people. However, with all things, there are people who are healthy and do not fit the standard measurements.
The purpose of this explanation is for you to understand where these tools providers use have generally originated from. A good provider will look at you as a patient and discuss what they see in person in addition to the metrics of your vitals. Many times for people who are working on trying to improve their body composition, seeing a diagnosis of ‘obese’ by their provider feels defeating. If this is you, then I encourage you to not accept the label as your identity, but become curious about why that label was given. It could have been inappropriately placed. Take your own metrics: like a waist measurement or an early morning naked bodyweight at home for a week straight. Gather data on yourself that you can take periodically and help you evaluate what your progress is.
Your wellbeing is your own.
Coach Sarah, FNP-BC, MSN