To study this, Anderson and her team looked at the most recent self-reported body mass index (BMI) data from 746,250 Canadians who were 18 years or older between 2009 and 2023.

Maybe because BMI was never intended to be an indicator of health and is just a simple and dirty math formula invented by a Belgian astronomer 200 years ago?

Is BMI Accurate? New Evidence Says No

For years, BMI—body mass index—has been the go-to tool for plotting our weight into categories. If your BMI number is 25 or higher, you fall into the overweight or obese category. So, does that mean that a BMI over 25 is unhealthy? Although many of us cling to the belief that a thin body is a healthy body, recent evidence suggests that’s not necessarily true.

URMC Newsroom (www.urmc.rochester.edu)

The really old, racist, and non-medical origins of the tool we use to measure our health

At one time or another, most people have calculated their body mass index or had it done for them. But despite its widespread use, it can't actually tell you much about your health. 

(www.abc.net.au)

BMI is just weight and height, a pound of muscle, a pound of fat, a pound of bone…

Doesn’t matter, a pound is a pound.

I failed BMI everytime I got measured in the military, they had to “rope and choke” which is a more time consuming method where waist/neck measurements were used. If I had still failed that, I’d have been given a buoyancy test as well for an even more accurate tests.

But it’s hard to call someone obese after you just measured the circumference of their abs…

When used as an average of a population BMI isbetter but it was made based on what weights were considered healthy for a white man 200 years ago, way before protein and weight training. And when the average person was like 5’6.

Lots of clearly healthy white men are labeled obese because of that. And no one else was even involved in coming up with the system, so they’ve always been getting wrong results.

It’s fucking insane we’re still using this ancient flawed method when we have so many better ways. Especially since the largest determiner of height back then was access to enough calories when young. Pretty much everyone is getting that now. And reaching their max height which is where BMI has always been the most flawed.

Like, obesity is an undeniable problem. But BMI is the least scientific metric we could be using short of some bullshit like astrology signs. The obesity epidemic too serious to fuck around like this

I’m curious why you think there’s an obesity epidemic if BMI as bad as you claim. Surely this means the problem is blown way out of proportion and the obesity rates are actually much lower?

Nope.

Because lots of obese people have healthy bmi’s

They’re usually the ones blowing badly defending it and haven’t had blood work done in a decade. They have no idea how unhealthy they are

Makes sense to me. I was at my most sedentary during the pandemic. That sedentariness kind of became a new normal. I’m still trying to change that

To study this, Anderson and her team looked at the most recent self-reported body mass index (BMI) data from 746,250 Canadians who were 18 years or older between 2009 and 2023.

Maybe because BMI was never intended to be an indicator of health and is just a simple and dirty math formula invented by a Belgian astronomer 200 years ago?

Is BMI Accurate? New Evidence Says No

For years, BMI—body mass index—has been the go-to tool for plotting our weight into categories. If your BMI number is 25 or higher, you fall into the overweight or obese category. So, does that mean that a BMI over 25 is unhealthy? Although many of us cling to the belief that a thin body is a healthy body, recent evidence suggests that’s not necessarily true.

URMC Newsroom (www.urmc.rochester.edu)

The really old, racist, and non-medical origins of the tool we use to measure our health

At one time or another, most people have calculated their body mass index or had it done for them. But despite its widespread use, it can't actually tell you much about your health. 

(www.abc.net.au)

BMI is just weight and height, a pound of muscle, a pound of fat, a pound of bone…

Doesn’t matter, a pound is a pound.

I failed BMI everytime I got measured in the military, they had to “rope and choke” which is a more time consuming method where waist/neck measurements were used. If I had still failed that, I’d have been given a buoyancy test as well for an even more accurate tests.

But it’s hard to call someone obese after you just measured the circumference of their abs…

When used as an average of a population BMI isbetter but it was made based on what weights were considered healthy for a white man 200 years ago, way before protein and weight training. And when the average person was like 5’6.

Lots of clearly healthy white men are labeled obese because of that. And no one else was even involved in coming up with the system, so they’ve always been getting wrong results.

It’s fucking insane we’re still using this ancient flawed method when we have so many better ways. Especially since the largest determiner of height back then was access to enough calories when young. Pretty much everyone is getting that now. And reaching their max height which is where BMI has always been the most flawed.

Like, obesity is an undeniable problem. But BMI is the least scientific metric we could be using short of some bullshit like astrology signs. The obesity epidemic too serious to fuck around like this

Sorry for the repeat questions but I’m not too knowledgeable on this; I thought BMI would have more false-positives (very muscular people for e.g.), but it seems you’re saying false negatives are a greater concern.

Would that be people with extremely low muscle mass so they have a BMI that might only show as overweight but due to body fat percentage they’re obese?

Oooof, was hopping we would not import this American tradition as well

Makes sense to me. I was at my most sedentary during the pandemic. That sedentariness kind of became a new normal. I’m still trying to change that

BMI isn’t a valid indicator of health for (young) people with lots of muscle mass from weight training (e.g., competitive athletes). Those people are a relatively small group in society, however. BMI is a somewhat valid indicator of health for most members of society, which makes it a reasonable population health metric. It has its drawbacks and there’s plenty of nuances to argue about but it’s very easy to use, and that handiness earns it its popularity

Well first off that paper is from 2025, but data collection for the OP study is as far back as 2009.

second this is the first line of the paper you indirectly linked:

current BMI-based measures of obesity can both underestimate and overestimate adiposity and provide inadequate information about health at the individual level, which undermines medically-sound approaches to health care and policy."

This study is not information at the individual level.

And here is a quote from later on in the abstract:

We recommend that BMI should be used only as a surrogate measure of health risk at a population level, for epidemiological studies, or for screening purposes, rather than as an individual measure of health.

E: OP’s study actually cites the new obesity definition in it’s methods to justify it’s use of BMI:

Not all individuals with a BMI of 30 or higher will have impaired health or increased risk of death, and some individuals with a BMI below 30 may also have obesity.18 However, for population-level screening and surveillance, the use of BMI categories as a proxy for obesity in adults continues to be recommended.9,14

citation 14 is that study referenced in Scientific American!

To study this, Anderson and her team looked at the most recent self-reported body mass index (BMI) data from 746,250 Canadians who were 18 years or older between 2009 and 2023.

Maybe because BMI was never intended to be an indicator of health and is just a simple and dirty math formula invented by a Belgian astronomer 200 years ago?

Is BMI Accurate? New Evidence Says No

For years, BMI—body mass index—has been the go-to tool for plotting our weight into categories. If your BMI number is 25 or higher, you fall into the overweight or obese category. So, does that mean that a BMI over 25 is unhealthy? Although many of us cling to the belief that a thin body is a healthy body, recent evidence suggests that’s not necessarily true.

URMC Newsroom (www.urmc.rochester.edu)

The really old, racist, and non-medical origins of the tool we use to measure our health

At one time or another, most people have calculated their body mass index or had it done for them. But despite its widespread use, it can't actually tell you much about your health. 

(www.abc.net.au)

BMI is just weight and height, a pound of muscle, a pound of fat, a pound of bone…

Doesn’t matter, a pound is a pound.

I failed BMI everytime I got measured in the military, they had to “rope and choke” which is a more time consuming method where waist/neck measurements were used. If I had still failed that, I’d have been given a buoyancy test as well for an even more accurate tests.

But it’s hard to call someone obese after you just measured the circumference of their abs…

When used as an average of a population BMI isbetter but it was made based on what weights were considered healthy for a white man 200 years ago, way before protein and weight training. And when the average person was like 5’6.

Lots of clearly healthy white men are labeled obese because of that. And no one else was even involved in coming up with the system, so they’ve always been getting wrong results.

It’s fucking insane we’re still using this ancient flawed method when we have so many better ways. Especially since the largest determiner of height back then was access to enough calories when young. Pretty much everyone is getting that now. And reaching their max height which is where BMI has always been the most flawed.

Like, obesity is an undeniable problem. But BMI is the least scientific metric we could be using short of some bullshit like astrology signs. The obesity epidemic too serious to fuck around like this

BMI is a somewhat valid indicator of health for most members of society, which makes it a reasonable population health metric.

That’s a half truth to some extent. Muscle mass isn’t the only thing that fumbles the BMI math. The calculation is also notoriously less useful for women in general, and for black/latino women specifically even more misrepresentative. And even outside those groups BMI isn’t really a “reasonable” health metric by today’s standards. But it ins’t totally useless either, so I guess it depends on what we mean with “reasonable”.

So you also agree that studies point that BMI doesn’t work very well in diagnostics? Because you’re replying the statement with a boldened sentence agreeing with gp.

Or perhaps was the point that it’s not true that “it doesn’t really mean shit now” since the BMI still has some usefulness at the population level?

My point is that the op article and underlying paper is valid and valuable.

but it seems you’re saying false negatives are a greater concern.

Someone with a bad BMI but healthy will get further testing and told they’re healthy…

Someone with a “good BMI” because they have bird bones and no muscle, just fat, will never have further testing done and always insist BMI is all that matters. You can see it anytime BMI comes up, people ignore all evidence that say they may need to look deeper than that single number.

Consider life in the 1830s to now, it would have been impossible for even the wealthiest to avoid exercise and consume as many calories as the average modern human. Shit just isn’t comparable.

There’s no logical reason to keep using it