The Body Mass Index is a common graph used for determining what a patient’s “normal” weight should be, based on their weight and height. Nevertheless, some have claimed it to be outdated, unscientific, inaccurate and even racist. Yet many doctors and weight loss authorities still use it and feel it is reliable. What is it and is it accurate?
I recently had a visit with my new doctor. Some people dread going to the doctor, but I’ve always looked forward to it. I’m generally pretty healthy. I used to be an athlete, and I still try to keep in pretty good shape. Not great, but pretty good, and usually a little better than my age bracket. A visit to the doctor is normally uneventful, and sometimes even complementary. (Full disclosure: I carry a bit more belly fat than I’d like to, which I credit to years of working long hours, and I’ve got a touch of osteoarthritis from an old car injury). When the COVID lockdown ended, I started hitting the gym nearly every day for an hour or two, and I put on a good bit of muscle, even if I didn't burn much fat.
I wasn’t surprised when the doctor told me, “You have to lose weight!” In fact, I heartily agreed, “I know! After a year in lockdown I could certainly stand to lose about 20 pounds.”
“NO! You have to lose 50 pounds! You’re almost morbidly obese!”
Obese?! For once, I was at a loss for words. Was he even looking at me? There was no one else in the room, but what he was saying didn’t make sense. I’m not a terribly large person, I’m only 5 foot 5”. Twenty pounds lighter and I’d look pretty good. 25 pounds would be pushing it a bit, but FIFTY POUNDS? I’d look like skeleton. Sure I’m a bit chubby, but obese? Morbidly obese?!
“It’s THE BMI! BODY MASS INDEX!” he snapped, “It’s your body composition!”
I thought quickly. “Are you looking at the scale for women, maybe?” I asked, even though he was quoting out of his head. He told me it was the same for men and women. The only factors to consider, he said, were weight and height, but that didn’t make any sense to me. A woman my height might reasonably be much lighter than I am, if she had delicate bone structure and very little muscle or fat. Aside from my spare tire, I’d added enough muscle to my chest and shoulders since the COVID lockdown that the new jacket I bought only a year ago didn’t fit over my shoulders anymore.
At this point, red flags were going up in my mind. I’d never had a doctor say anything like this to me before, and for me, his judgement was coming into question, because what he was saying didn't sound scientific. “You know muscle is heavier than fat?” I felt compelled to ask. He insisted that it didn’t matter. It was all the same, he said, only height and weight mattered. I was flummoxed.
As far as he was concerned, there was no more to discuss. BMI was everything there was. All of this shook my faith in the doctor, but maybe he was right and I was wrong. He was the doctor after all. Could I actually be the thinnest obese man in history?
As I left the office, I suppressed the urge to eat an entire pizza in protest, and decided to learn a bit about the BMI when I got home.
I Have to Educate Myself
As a motivational coach, I’ve dealt with a lot of weight loss clients. I deal with their feelings and motivations, but I leave the technicalities of weight and diet to their health care professionals. I can help the clients get over their mental and emotional hurdles, but I don’t tell them what goals to reach for. So I knew about the Body Mass Index (BMI), but I didn’t know the specifics.
What little I did know was that the very concept of “body composition” is the ratio of muscle to non-muscle tissue, and for practical purposes of weight loss, what mattered was the percentage of fat versus non-fat, and it’s common knowledge that muscle weighs more than fat of the same volume.
I also knew there were other variables involved. Gender matters. Males tend to have denser bone and muscle than females as a result of hormonal changes at puberty. Another thing to be considered is age. A 20-year old is usually going to have a stronger metabolism and naturally fitter body than a 40-year old, even if the 40 year old exercises a whole lot more, and I’m 60! (I don’t look a day over 58, though). Race and genetics are another issue that has to be factored in. Different ethnicities store fat in different ways and in different parts of the body, and may not offer the same weight/height ratios.There are probably other specific variables as well.
There it is, the BMI chart. And sure enough, It says I’m vastly overweight. But you know what? It might say you’re overweight too! You’ll notice there’s no accounting for any of those other, obvious, variables. I thought there might be a more sophisticated version of the chart and searched for it on the web, but there aren’t any. Maybe the doctor was right, but to my mind, simple common sense says this chart is both incorrect and also unscientific--two variables, height and weight, simply aren’t enough to accurately gauge a person’s health.
It didn’t take me long to discover a whole lot more. There’s a lot of material about the BMI available, but it wasn’t the dry science I was expecting.
The Quetelet Scale
Are you Belgian? Are you more than 150 years old? If you answered “no” to these questions, the the BMI may not be right for you!
The BMI, was originally known as The Quetelet Scale, after it’s creator was Lambert Adolphe Jacques Quetelet (1796-1874). Quetelet was possessed of one of those brilliant, inquisitive, scientific minds which this period in history produced so many of. He focused his considerable mental powers on many aspects of the natural sciences and the arts, but his two greatest passions were astronomy and mathematics. Stars aside, He felt that numerical statistics could capture and describe the idealized perfection of nature (which he believed to be graphed as a bell curve). He further felt that once that mathematical ideal was established from a small pool of data, it could be generalized out reliably to a much larger population. To that end, he compiled statistics on all kinds of things, including crime rates, marriage rates and, since he was artistically inclined, perfect human proportions. He came up with the formula for the ideal human body based on the formula: weight x height2. In other words, 'the weight increases as the square of the height' This formula was based on measurements from the humans he happened to have at hand, and is sort of the way you's measure the volume of a milk bottle. He published his findings in 1830, and the numbers have not been revised since.
He was not a doctor. He didn’t know much about medical or structural variations or about human anatomy, and he didn’t intend the Quetelet Scale to be a diagnostic tool. It was more of a philosophical exercise.
The Quetelet Scale enters a New Century
Ancel Benjamin Keys (1904 – 2004) was another brilliant scientist of a different century, and a trailblazer in the field of nutrition. We can credit him for the our modern understanding of the relationship of cholesterol to heart disease, the benefits of the Mediterranean diet, and a number of other discoveries which have become the cornerstones of modern nutritional science. He helped formulate special meals for the soldiers in WW2 based on their caloric needs and it’s rumored the (in)famous K-Ration of WW2 got the “K” in Keys’ honor.
One of his grandest research projects was the Seven Country Study, which charted the relationship of diet and longevity (particularly heart disease) in seven different countries over a period of several decades. He followed the health histories and measurements of hundreds, possibly thousands, of people over the years in order to get a large sampling of data. In order to process and quantify all the data he was collecting, he chose the Quetelet scale out of convenience, because out of all the existing scales for body mass, he felt the Quetelet Scale was mathematically the most complete, and therefor, convenient for his purposes. When he published some of his findings in 1972, he included the Quetelet Scale, which he renamed The Body Mass Index. But he was clear that it was really only useful for processing large amounts of demographic data, not for use on individuals.
So there we have it. An academic exercise conducted by Belgian astronomer nearly 200 years ago in the search for mathematical perfection, picked up in 1972 as a convenient demographic tool. It does not figure things like muscle vs. fat, activity level, age, gender, nutrition habits or an individual’s genetic variations. It simply calculates the volume of a human body as if it’s a jam jar.
So why on earth would modern doctors today, people of science, take up this bit of outdated ephemera when modern tools and methods could provide better data? To be fair, a lot of medical experts neither use nor endorse it. Many have come up with better alternatives. Yet some doctors have accepted it without questioning it’s obvious flaws. Many sources on the internet present it as simple fact without any discussion of it’s failings. According to what I’ve been able to glean, many medical schools are still teaching it, and the students are accepting and absorbing it (even though their own eyes are probably giving them contradictory data!). So why would medical schools promote something that one’s own sense contradicts?
I don’t know. According to some of the sources below, the BMI was picked up and endorsed not by medical experts, but by health insurance companies who felt is assessed the health risks of their customers accurately (and with a good safety margin for the company, I’d imagine). Apparently, a lot of people who teach it never even thought to question it. It’s just been passed along by tradition.
Are There Better Ways To Measure Fat?
If you want to get an accurate gauge of your weight and health, it goes without saying that you should consult with a health care professional who is trained and qualified. They will know the best course of action for you regarding testing, and for helping you reach your own health and fitness goals.
There are a number other more thorough body mass indices. One that attempts to address the shortcomings of the BMI is the ABSI (A Body Shape Index). The ABSI was created at City College of New York, with an initial pool of test subjects that included over 14,000 people, and it has since been reaffirmed with even larger sample groups. It is still a generalization, but at least it includes more of the obvious, important variables: age, gender, waist diameter as well as height and weight. If more exacting tests are needed, there are a number of them. I’ve listed the common ones below.
Body Composition Testing Methods
Skinfold Caliper Test-- This is a very common test with athletes and body builders, and is considered to be an easy and fairly accurate test for measuring subcutaneous (beneath the skin) fat. It uses a special caliper which pinches the skin in several specific places around the body to measure the thickness of the fat underneath. The thicker the pinch, the more fat. These measurements are then calculated to get an overall average. It can also indicate which parts of the body have the most or least fat stored in them (which can be an important finding in certain situations). There are several obvious shortcomings of this test. It can’t measure fat stored deep inside the body, only under the skin. It can also be inaccurate if too much or too little pressure is applied with the calipers, or if the pinch is too big or too small. Individuals may also have more or less dense skin, regardless of the fat beneath.
Bioelectric Impedance Analysis-- This utilizes a device that sends an imperceptible electric current through the body, and measures the amount of electrical resistance the body offers. Since fat has a greater electrical resistance than muscle or water, measuring the resistance will tell how much fat is conducting the current. For the test, several electrodes are attached to various parts of the body. The test itself can be done fairly quickly. Some sources feel it’s reliability is questionable, just because there are so many things that can potentially throw off the results--exercising before the test, dehydration, skin temperature, room temperature, medication, etc. Nevertheless its fast and convenient and a good starting point. There are even home devices you can hold between your hands, although their accuracy seems questionable.
Hydrostatic Weight Measurement-- This is also considered a very accurate measurement of body composition, though some sources indicate it’s considered a bit old fashioned, perhaps due to the complexity of test. An individual’s weight is measured before the test (dry), and then the individual is submerged in a tank of water and weighed again. The theory behind it is that fat is more buoyant than non-fat, so the individual will weight less when submerged. By noting the difference between the wet and dry weight, they can get a pretty accurate measurement of the actual amount of fat by weight.
Dual-energy X-ray Absorptiometry (DXA or DEXA)-- This involves a special scanner that creates an X-ray imaging of the entire body that also measures the density of the various structures--bones, organs, fat and muscle. This is obviously an extremely accurate way of measuring and seeing the fat in different places, and it can also measure density of bones and other organs. It generally takes about 15 minute or less to do.
Thoughts About The Other Controversial PointsA number of sources (including a few of the links cited below) state the BMI to be “racist.” By now we’ve established it isn’t a reliable index for any other group except 200 year old Belgians. I don’t know if Quetelet even knew that different human genetic groups had different anatomical specifics, but most likely, he didn’t know or consider it. He wasn’t a medical man. However it’s fair to say it’s application by modern medicine to a broad range of race and body types is, at least, misguided.
In fairness, the BMI isn’t entirely inaccurate, either. It was based on measurements taken from “average” (not physically active) 19th century Belgian men, who tended to be somewhat smaller, and lighter due to the their diet and living conditions. So while modern 20-21st century American and European people across the board are a bit bigger and heavier, the BMI does seem to be more accurate with younger, less physically active women (physical activity tends to add muscle mass and throw off the accuracy).
When I was discussing this with someone, they asked why the gender discussion is only in terms of male and female and ignores more of the gender variations that are accepted in the 21 century. I have no answer to that, since I didn’t find any data about that. I imagine that this is why it’s important to have qualified professionals interpret the data, and that we’ll see more variation in the future.
Note that this article is purely for information and perhaps entertainment value, and is not intended to provide medical advice or diagnose anything. Always consult with the appropriate, qualified professionals about all your health concerns.
Quetelet and the BMI
(This excellent article has a much more detailed historical and scientific discussion than most)
BMI And Race
Ancel Keys and the Seven Country Study
Better Body Weight Measurements
(web page has built in calculators for six different methods)
Bioelectric Impedance Analysis
X Ray Imaging
Hydrostatic Weight Measurement