It was designed for analysis of populations on average. Then it was applied to individuals and never should have. Variations in body structure average out over large populations, but not at the individual level.
this post was submitted on 17 Apr 2026
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BMI was never discredited. It's always been intended as a population-level estimate of obesity. There have been a number of studies over the years that have correlated other health outcomes to BMI, but those things are intended to be population-level correlations. For example BMI is correlated with average expected life span, where a BMI in the "healthy" range is correlated with longer average lifespans, and both under or overweight BMIs are correlated with shorter average lifespans. Your specific health situation may vary.
MRI or DXA scans can more accurately determine body fat percentage to determine obesity. Comparing those with BMI has an error rate of around 20% of people being miscategorized as under or overweight.
Bottom line, don't be sedentary all the time, get physical activity and eat a healthy diet instead of getting too hung up on what metrics are best. Progress over perfection.
I like Harvard's Nutrition Source for science-based nutrition info that's easy to read.
For example BMI is correlated with average expected life span, where a BMI in the "healthy" range is correlated with longer average lifespans, and both under or overweight BMIs are correlated with shorter average lifespans.
Actually, there's a curve where all cause mortality is lowest at BMIs that are slightly overweight, between 25-30 kg/m^2 :
https://pmc.ncbi.nlm.nih.gov/articles/PMC11051237/
So the traditional "overweight" range appears to be slightly healthier overall than the "healthy" range. Perhaps because some healthy people have higher lean tissue mass (muscle, bone density, etc.).
The intended use is to get a quick overview of populations and it works great there. For individuals the Waist to Height ratio and Waist to Hip ratios are better quick scan controls.
It's also good as an estimate if you hugely widen what's taken as normal. 80 is just too damn high and 12 for an adult is just too damn low.
I mean, sure, but unless the physician is blind is bmi really needed at that point? :)
Works?
What do you mean "works"?
It's an observation from collected data, nothing more.
Worked how?
It fully works as intended. It's only when people try to use it for other purposes that it fails. It's an estimation tool, nothing more or less
It's just a method for guestimating how much of a body is lean mass vs fat. There are a few others, such as the Navy method, that are more or less accurate for different body types
The current state of the art is DXA scanning:
It's just a method for guestimating how much of a body is lean mass vs fat.
It was created to estimate the amount of obesity in a population, not on the individual level. It also breaks down for tall and short people.
yep, that's what the guess in guestimating means, it was always a statistical approach to solving a problem that requires disecting a person otherwise. That's why the x ray based scanning is the current state of the art.
TIL the guess in guestimating means using tools to describe a population on the individual.
yep, it's the wrong tool for the job, like measuring planetary distances in football fields.
From what I have read, it is body-fat measure that we ought be using, & the plastic-calipers cost something like $5-10, online.
I'd read that in some scientific news thing, a few years ago, sorry don't remember which one.
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The body fat calliper method is extremely dependent on the person doing the measurement, so it’s more useful for measuring progress. The Navy Method is slightly less variable, and is a pretty good balance between cost, accuracy, and reliability if you’re looking for something. Not as good as DEXA, far better than body impedance, and more accurate than callipers.
Body fat definitely is a better method, up to a point - once someone is definitely into the “obese” or “underweight” on the BMI, there’s a good chance of the person is unhealthy in some way. Bodybuilders achieve worryingly low body fat % with “obese” BMI score, but they can still have plenty of other markers that say they’re unhealthy, and underweight is underweight. But my BMI is ~25 (“overweight”) and ~15% body fat; I’m ok.
A lot of people who are 50% body fat and have a BMI of 35 love to hear that the BMI is flawed.
I just remember as a teen at 16 and my PCP had it in the waiting room. And he swore by it. At 16 I was 6 foot and weighed about 150. And he said I had to much body fat. That I need to go on a diet. My mom the nurse was about to tear him a new asshole before i interrupted and asked Does a fifth of whiskey and a pack of Lucky Strikes a day count? You could hear a pin drop after I said that.
The UK's NHS BMI calculator puts the BMI of someone around that age, height and weight at the 54th centile. It's hard to be more average.
If you consider only the healthy part of the BMI spectrum you were still barely more than average (58th centile).
Your PCP's motivations are hard to determine, but a diet does seem a bit extreme. Without further information we might conclude that he would have wanted to put near half of your country's teens on a diet.
16 years old 6ft tall 150# works out to 183cm 77kg BMI20 (lower mid normal) and I’d put you on a diet and exercise program for sure. To gain weight and muscle. Muscle mass is correlated strongly with quality of life in later years, and you’ve described a string bean. Maybe a skinny fat string bean, but still.
LMAO....so sorry ...I am really no sarcasm...but never thought I would ever see in a sentence a skinny fat string bean lol. No my pcp was talking about losing more wieght.
They said you needed to lose weight at 150‽ I'm also 6ft but I have 100lbs on you and I still am dense enough to sink in ocean water. My build would have made your doc have a stroke.