Here are 10 reasons that the BMI is bogus according to NPR:
To save you a click:
The person who dreamed up the BMI said explicitly that it could not and should not be used to indicate the level of fatness in an individual.
It is scientifically nonsensical.
It is physiologically wrong.
It gets the logic wrong.
It’s bad statistics.
It is lying by scientific authority.
It suggests there are distinct categories of underweight, ideal, overweight and obese, with sharp boundaries that hinge on a decimal place.
It makes the more cynical members of society suspect that the medical insurance industry lobbies for the continued use of the BMI to keep their profits high.
Continued reliance on the BMI means doctors don’t feel the need to use one of the more scientifically sound methods that are available to measure obesity levels.
It embarrasses the U.S.
Some of those are more opinion than fact
Let’s add one more:
It was created by a mathematician by the name of Adolphe Quetelet.
He also founded the science of anthropometry and developed the body mass index (BMI) scale, originally called the Quetelet Index. [ 4 ] His work on measuring human characteristics to determine the ideal average man (“the average man”), played a key role in the origins of eugenics . [ 5 ] [ 6 ] [ 7 ]
Any list which includes “it makes cynical people suspect things” and “it embarrasses the US” in its reasons is a terrible list, and the fact that they’re including such garbage reasons makes all of their other claims suspect as well.
The article has a lot of statements about how it’s not accurate for a subset of the population:
I don’t think the American population would generally be classified that way (as fit and having little fat). In general, Americans are sedentary and overweight. BMI likely is incorrect for people who have a lot of weight from extra muscle, but that is just a small percentage of the overall population. In general, the BMI is a simple way to get a reasonably accurate idea of how someone’s fat may impact their health. The best way is with a body fat test, but that can be expensive and time consuming, as people will have to go somewhere to have it tested. BMI can be done by anyone at home.
Also, he doesn’t provide any disproving data. One thing he could have done is provide body fat percentage numbers for different people at different BMI values. If he can show that there is not an appropriate statistical correlation between BMI values and body fat, then it would help prove his point. But he’s just giving his opinion. My opinion is that his insurance rates went up because of his BMI value and he’s expressing his displeasure by trying to discount BMI completely.
8. It makes the more cynical members of society suspect that the medical insurance industry lobbies for the continued use of the BMI to keep their profits high.
Insurance companies sometimes charge higher premiums for people with a high BMI. Among such people are all those fit individuals with good bone and muscle and little fat, who will live long, healthy lives during which they will have to pay those greater premiums.
I’ve also heard that the diet industry lobbied for the change in the BMI levels that were done in the early 2000s
10. It embarrasses the U.S.
It is embarrassing for one of the most scientifically, technologically and medicinally advanced nations in the world to base advice on how to prevent one of the leading causes of poor health and premature death (obesity) on a 200-year-old numerical hack developed by a mathematician who was not even an expert in what little was known about the human body back then.
This was a four minute interview on NPR, the text is the transcript for the interview. What you are expecting is not suited for that format.
Here is a link to his info page:
Dr. Keith Devlin is an emeritus mathematician at Stanford University, a co-founder and Executive Director Emeritus of the Stanford H-STAR institute, a co-founder of the Stanford mediaX research network, and a Senior Researcher Emeritus at CSLI. He is a World Economic Forum Fellow, a Fellow of the American Association for the Advancement of Science, and a Fellow of the American Mathematical Society. Much of his current research is focused on the use of different media to teach and communicate mathematics to diverse audiences. In this connection, he is a co-founder and President of an educational technology company, BrainQuake, that creates mathematics learning video games. For several years he worked on the design of information systems for intelligence analysis. Other past research interests included: theory of information, models of reasoning, applications of mathematical techniques in the study of communication, and mathematical cognition. He has written 33 books and over 80 published research articles. Recipient of the Pythagoras Prize, the Peano Prize, the Carl Sagan Award, and the Joint Policy Board for Mathematics Communications Award. In 2003, he was recognized by the California State Assembly for his “innovative work and longtime service in the field of mathematics and its relation to logic and linguistics.” For many years he was “the Math Guy” on National Public Radio.
He is in reasonably good shape. He isn’t skinny, but he is no where near fat.
Now, he is a statistician, not a biologist. He probably has a problem with the bad statistics.
I don’t agree with you. I’ve known people from every size from super-skinny to nearly too big to move, and from people who are exercise addicts to people who complain if they have to walk across the room. And these are continuums. No one goes for unfit to fit in a day.
So. Here’s my problem with BMI - it discourages exercise.
When I was a teen, my mom (who pressured me to diet), told me “Don’t exercise, it will cause you to gain weight”
I’ve known a couple of people who said “I’ve been exercising regularly, but I haven’t lost any weight?”
Muscle weight is more dense that fat weight. If you exercise, you can easily lose inches while not losing weight. If you only use the scale as a measure of health, you will be discouraged that your effort is not changing anything.
I’ve seen news articles come out every few years that say that exercise will not help you lose weight.
Exercise is probably a greater predictor of health than weight could possibly be. But weight is easy to measure, how fit someone is, is much harder.
The inverse of “People who are fit can have high BMI” is "People who are not fit can have low BMI:
Reasons #1 through #7 are basically variations on the same (albeit legitimate) complaint. For #8, there are so many things that insurance industry lobbies use to maintain their profits and valuation that this barely even falls above the ignore line. On #9, most general practitioners have only vague notions about diet and exercise, so whether they use BMI or another “more scientifically sound methods that are available to measure obesity levels”, their guidance is still going to be generic and mostly useless to people who are overweight or obese. As far as embarrassing the US, believe it or not BMI is also used in Europe as a metric to assess obesity, and in the range of bad medical practices is far from the worst thing the American Medical Association has done, notwithstanding all of the multitude of actions and beliefs that Americans in general should be embarrassed about.
BMI as a singular metric provides a flawed interpretation of excessive weight and obesity that does not incorporate either musculoskeletal body type nor differentiate between lean muscle, subcutaneous fat, and visceral fat. Certainly at the margins is not a good estimator for unhealthy conditions, but you don’t have to look very hard at Americans and their dietary and physical habits to concur that there is a major problem with obesity even before you start looking at the statistics on chronic health conditions in which obesity is a significant contributor. The “fat acceptance movement” has tried to convince people that carrying a lot of extra visceral and subcutaneous fat is normal and healthy despite all medical evidence to the contrary, and while its message of not shaming people for being overweight is a positive and valuable one because shame doesn’t work as a corrective measure, the ‘acceptance’ of such conditions and that consuming copious amounts of nutrition-free ‘junk food’ is a-okay is not.
It’s true that some people have more difficulty regulating their weight or maintaining a healthy diet than others but baring physical ailments, chromosomal abnormalities, and chronic health conditions, maintaining good body composition is an artifact of dietary education and building good eating and physical movement habits. Not everyone can have six pack abs, but any basically able adult under the age of 70 should be able to walk a mile in twenty minutes, climb five flights of stairs without running out of breath, pick up a bag of sand and carry it a hundred feet, and fit through a normal 30” closet or interior doorway without squeezing through.
In general, I’d say that the complaints about BMI and calories in, calories out both rest on imperfection.
Nothing is perfect. You could put together a health metric based on lean weight over total weight, average fitness time per day, age, gender, how much kale they eat, and how many cute puppies they wake up to in a day but - for this specific individual - you forgot to include the total amount of exposure that they get sand blasting lead blocks into sculptures at that new job next to the chlorine factory and wow were your life expectancy calculations way off!
BMI is a blunt and simple tool that you can perform on most people, using cheap and minimal equipment - and get a metric that can be factored in with 30 other metrics, and give a fair guess as to that person’s health prospects in most cases.
Most of the angst over its imperfection isn’t that it’s imperfect, it’s that people don’t like that they’re not in the green zone.
The bodybuilders outside of the green zone on the BMI chart aren’t the ones writing big lists of why it’s a sham metric. For the ones writing the lists, probably it isn’t.
FWIW there is some promotion of using a different simple to measure metric: the body roundness index (BRI). NYT recently had an article on it but here is some actual source material.
Do you know of any references that examine if there’s a correlation of BMI to body fat percentages? A close correlation would seem to mean that BMI would be a useful way to approximate body fat percentage.
It’s been studied. I haven’t done this work for 15 years, so I don’t have a handy go to list of references. I think the correlation is in the 0.60-0.80 range, but I could be off. And like “predictive” people often don’t understand what a correlation means: “all your anecdote shows is that the correlation should be less than 1, which is what I just said.”
Having said all that, yeah, BMI can be a lousy indicator of any single individual’s health, but goes a really long way towards telling us that being over weight is a risk factor for heart disease, cancer, diabetes (2), stroke, mental health problems, kidney disease, etc.
Sure, but there was also already body fat measurement techniques, multi-metric formulas, etc. that could be used.
Before screws were invented, there were other more complicated and more robust forms of wood joinery than nails but most stuff was still done with nails. At that time, people weren’t out writing political pamphlets that “nails are some conspiratorial sham against them that should never be used for any practical purpose”. Everyone understood just fine that a nail is simply sufficient and cheaper for the majority case. You bring out the complicated, 3D joinery and wood glue for special situations.
The invention of the screw didn’t change any of that. Inventing the screw wasn’t what made the diatribes go away. They never existed to begin with, because why would there be?
Although it has some usefulness it is, in my opinion, vastly oversold.
To really understand a person’s health you have to look at multiple indicators. Athletes who are genuinely fit but fall under “obese” in BMI measurements can be seen to be healthy by other factors like resting heart rate, blood pressure, waist-to-hip ratio, fasting blood sugar, and others… which are all a bit more tedious/difficult to measure.
There are people with “perfect” BMI’s who nonetheless are unhealthy and have deplorable resting heart rates, sky-high blood pressure, etc., etc.
Actual, competent medical professionals should know and understand these things and be able to appropriately fit BMI into their assessments… but not all of them do. Or take the time to do so.
Meanwhile, insurance companies want cheap, easy ways to label people, and/or to pigeonhole them, charge them higher rates, etc.
And some people will happily blame every little problem a person has on that BMI number and use it to bludgeon those people and tell them it’s their fault that they have to deal with X or they wound up with Y syndrome.
It’s a mess.
But we live in a sound-bite society that doesn’t want to exert even minimal effort on nuanced understanding.
