If you have a lot of abdominal fat then you also have visceral fat so it's just a proxy

How many ECGs can you sell vs how many other snake-oil products? :)

(Edit: This is intended to be sarcastic. I agree 100% with the comment)

(Edit 2: Added the smiley face)

> BMI is really easy to measure, and is mostly accurate, that’s why it’s so pervasive.

BMI is easily misunderstood by people who know just enough to see that it’s imperfect, but not enough to understand why it’s still a valuable screening tool.

I’ve been in the “overweight” BMI range with low body fat before. It’s not too hard to get there if you’re lifting weights and paying attention to your diet consistently for years, but it takes a lot of work to get there. It doesn’t happen accidentally except for people who win some genetic lottery to build a lot of muscle and keep body fat low without trying.

Getting all the way to the obese BMI range while having healthy body fat is only happening for people with an extreme dedication to body building and diet (and let’s be honest, a lot of the people in this category are manipulating hormones too).

Yet whenever BMI comes up some people try to dismiss it as too flawed based on these possible edge cases. The edge cases for BMI exist, but that doesn’t mean it’s not useful. It’s a good general purpose screening tool with numbers that are available. If someone has more precise measurements available, those should be used instead. BMI is a really good first pass screener to determine if a closer look should happen.

Yes, it is a pretty high level metric with good correlation a bunch of diseases, but really many of these is because it is ALSO correlated to percent of fat, which is often the more relevant metric. But as you said BMI is so much simpler to measure.

Many active gym people have pretty high BMIs but fairly low fat (because muscle is dense), and unsurprisingly have better outcomes than the average person (if you ignore the share that uses/overuses anabolic steroids and co)

How accurate is it, in practice, for a given individual? I'm not that out of the ordinary proportion wise. I have a slightly longer torso and arms versus my legs, a somewhat muscular-ish baseline and broad shoulders, but I accumulate fat almost exclusively abdominally. My teenage self, lifetime peak of my fitness, no visible body fat, hyperactive football player, qualified as solidly overweight. If I was to listen to it, I'd be called obese before I noticeably start to show body fat.

I often wonder far from the median I am in this regard. I was under the impression that it was pretty accurate for assessing populations, but fell apart very quickly at the individual level. How many "normal"/otherwise healthy people do fall outside BMI's numbers?

But it's actually not just being "overfat".

It's specifically a high level of visceral body fat.

Genetics determines which parts of the body gain fat first as you gain fat overall, and some people have the unfortunate genetics to gain it first viscerally and some people have the fortune to gain it there last (and everything in between).

This means that you can have different people with the same body fat percentage but drastically different disease risks.

But yes this was also known already.

That's why it's been recommended to take a waist measurement alongside BMI to get a much more informative screening tool. Waist-to-height ratios are another alternative.

Yeah BMI is sort of a 'good enough' technique but also has some very obvious areas that it can miss. If you fall outside the typical fat to muscle ratio is a good example.

Genuine question: What is the difference between overfat and overweight? Isn’t the extra weight in an overweight person comprised of fat?

They have. BIM is usually talked about in the same breath as waist circumference which would be a better measure of abdominal fat.

I

Same for me, no one considers BMI to be a good indicator of anything, but it is better than nothing, and more importantly, it is super simple.

Any idiot with a bathroom scale and a measuring tape can do it. And by adulthood, height doesn't change significantly and you probably know it, so you may not even need that measuring tape. Other metrics need specialized equipment, error prone or complex procedures, etc... I don't even know how to make a waist measurement. Where exactly? How relaxed should the subject be? How long after eating?...

That's the value of BMI: simple repeatable. Not the best but enough to get and idea and make statistics.

A waist measurement is the cheapest and simplest way other than just looking.

You want to make sure you measure under similar conditions, like in the morning after relieving yourself (for example).

If it's too high, losing a ~0.5-1 lbs per week while strength and endurance training with progressive overload will get it down sustainably.

https://www.barbellmedicine.com/blog/visceral-fat-waist-vs-w...

whats wild is there are people who look very fat - who have lots of subcutaneous fat, who don't have visceral fat. The excessive subcutaneous fat can be hard on your joints but doesn't seem to correlate to other health issues.

There are scans for like $50 that will tell you. Google Dexa scan or something like that.

My problem is it’s usually the second guy advancing this argument.

This is a common misconception. BMI while an ok population metric, for individual's the biggest problem with is its poor sensitivity - it fails to classify people as obese who are obese.

Using your 6 3" male as an example, they are significantly more likely to be clinically obese (using waist circumference, body fat % etc) at a weight lower than BMI cut-off of 240 lbs.

BMI is not a good metric for really short and really tall people.

The "ideal weight" of a person is proportional to height to an exponent somewhere between 2 and 3. Simple physics would say 3 but because tall people are not just scaled up copies of small people, it is closer to 2 in practice, maybe around 2.3, but we say 2 because it is easier to calculate.

The downside is that BMI overestimates the "ideal weight" for short people and underestimate it for tall people. But BMI is not great at capturing exceptions anyways, so there is little interest in "fixing" this.