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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.
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.
Works?
What do you mean "works"?
It's an observation from collected data, nothing more.
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.
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.
The only people who hate BMI are fat people, and US health agencies who hate the fact that the rate increasing out of control.
Fastest way to decrease your BMI is to lose a leg. The fastest way to increase it is to lose two.
Not all mass is fat, and not all mass is the same.
BMI is a general guideline that offers a reasonable approximation of body mass at the population level. That it also offers a reasonable estimate on the individual level, when all other factors are taken into account, is a plus.
Medical practitioners aren't out there widely telling otherwise obese people with missing limbs that they're a perfectly healthy weight or that all mass is fat.
When you read unverifiable anecdotes about a dumb doctor telling a power lifter that they are obese, don't take it as gospel. When your doctor tells you that you're a perfectly healthy weight because you're missing a leg, even though you don't exercise, eat like shit, and have a 50 inch / 125 cm waist, that's when you start asking questions and find a new doctor. Most of them aren't like that.
this post was submitted on 17 Apr 2026
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