BMI charts are as ubiquitous to doctors offices as stethoscopes and thermometers. Used as a quick and easy way to measure adiposity (quite inaccurately, as we’ll get to), BMI has somehow become a proxy for measuring health by assigning people categories of underweight, normal, overweight, obese, and morbidly obese.
Even those who would defend the use of BMI would admit it has it’s problems. Even before my practice aligned with Health at Every Size, I thought BMI was 90% useless. Still, I don’t think people realize quite how bunk the BMI scale actually is. Shout out to whoever started that BMI = BS Measuring Index on IG, because I think that’s the most accurate description I’ve heard (if you know please tell me so I can give credit!). While there is limited use for BMI in research, there is ZERO use for BMI in assigning or predicting health.
The MANY Problems with BMI
BMI wasn’t designed for use on individuals.
BMI was actually crated by a mathematician in the mid-1800s as a way to measure the average weight of a population. The creator himself stated that it was NOT for use in individuals. Not only that, but the population measured was in no way representative of the diverse populations it’s being used on today. BMI was developed on a group of all men - no women. And because it was Belgium in the mid-1800s, I’m going to guess it was mostly, if not all, white men.
BMI doesn’t distinguish between different types of body mass.
BMI doesn’t distinguish between fat, muscle and skeletal tissue, or fluid weight. There are many things that are associated with fitness and good health that would make someone’s weight higher. Muscle is a great example. Because it weighs more, many athletes are technically overweight or obese, despite being pretty much specimens of good health. Bone is another example. Denser bone is associated with better health, but it also weighs more.
“Overweight/Obese” does not mean unhealthy.
Weight is not a proxy for health. Approximately 25% of “normal” weight people have an abnormal cardiometabolic profile, while approximately 50% of those who are “overweight” and 30% of those who are “obese” have normal cardiometabolic profiles. Except for at statistical extremes (high AND low), weight is only loosely correlated with health outcomes. And please note correlation is very different than causation.
The BMI equation itself is kinda screwy.
BMI is calculated by dividing weight by height squared. From what I understand, the mathematician who came up with the formula decided to square height in order to make his data work - it wasn’t a formula he came up with in advance. Forcing your data to fit by changing equations is not good science. Also, by squaring height, it actually makes taller people have a higher BMI.
Focusing on BMI ignores behaviors.
The argument for using BMI is that it’s a quick, easy and expensive tool for assessing a (supposedly) modifiable risk factor. But you know what else is a pretty quick way of assessing modifiable risk factors? Asking about just four behaviors - fruit and vegetable consumption, physical activity, smoking, and alcohol use. If you are worried about your BMI, please know that by eating fruits and veggies, getting moderate physical activity, not smoking, and limiting alcohol consumption, the statistical health risks associated with higher BMIs are completely erased! Can you imagine what visits to the doctor would be like if they screened for these things on intake instead of taking weights, and provided resources for those who were interested in making changes?
Fat isn’t a disease. It’s a naturally existing body size.
Bodies exist in a wide range of shapes and sizes - curvy, plus sized, fat, very fat, large - there’s many different descriptors people like to use. Assigning a disease (i.e. obesity) to a body size that would naturally exist, even if everyone was eating healthy and exercising regularly, is dehumanizing and promotes weight stigmatizing behaviors and institutional policies.
Have you been told to lose weight for health?
If so, I’m sorry that you were given lazy medicine. It’s really unfair to you, because weight is not something entirely in our control - nor is health for that matter. By hinging health on weight, it distracts from actual positive behaviors that can promote better health, and creates a weight stigma that actively harms health. In my practice, we’re committed to providing weight inclusive care, which means focusing on your behaviors with food, and relationship to it - NOT an arbitrary number on a scale. Learn more about my practice here, and contact me to set up a free 15 minute phone consult to see if we’re a good fit to work together.
Wildman et al: The obese without cardiometabolic risk factor clustering and the normal weight with cardiometabolic risk factor clustering: prevalence and correlates of 2 phenotypes among the US population Arch Intern Med. 2008.
Be Nourished: Debunking the BMI Myth.
Flegal et al: Excess deaths associated with underweight, overweight, and obesity. JAMA. 2005.
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