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Comment by JohnMakin | Hacker News Reader

This is a tricky subject, because as this article mentions, BMI is an imperfect measure of health. So, we should probably stop using it. I am 26.2 BMI but I am an athlete. I have a higher body fat than I would like, particularly around parts of my mid section, but otherwise am in good heart health and all blood tests come back great. Yet, I will still be told to lose weight by most primary care doctors, based purely on BMI.

Unfortunately this fact has been hijacked by "fat positive" movements like Health at Every Size. They take this fact that BMI is an imperfect measure of health and stretch it waaaaay too far in my opinion, with most supporters translating it as "I can be healthy no matter how fat I am," which is definitely not true. There is an absolutely positive correlation with body fat, weight, and health. Unfortunately sane discussion on this is practically impossible no matter where you stand.

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Would it be reasonable to say that BMI is a bad measure at an individual level, especially at values close to ideal range but at the same time it is a useful measure at population scale? As stated on the NHS Scotland website:

"BMI is used to categorise people’s weight. BMI charts are mainly used for working out the health of populations rather than individuals.

Within a population there will always be people who are at the extremes (have a high BMI or low BMI).

A high or low BMI may be an indicator of poor diet, varying activity levels, or high stress. Just because someone has a ‘normal BMI’ does not mean that they are healthy.

BMI doesn’t take account of body composition, for example, muscle, fat, bone density. Sex and other factors which can impact your weight can also lead to an inaccurate reading. As such a BMI calculation is not a suitable measure for some people including children and young people under 18, pregnant women and athletes."

It's only useful at scale if people at scale are unhealthy.

If the norm was to be like OP, then BMI would not be useful at scale.

Given that you need to know the outcome to determine if the measure is valid, it rather defeats the purpose of using the measure at all.

Not really, it’s one variable amongst many. If the general population also has poor diet, we can assume the BMI is not because everyone has an exemplary physique

> Unfortunately this fact has been hijacked by "fat positive" movements like Health at Every Size. They take this fact that BMI is an imperfect measure of health and stretch it waaaaay too far in my opinion, with most supporters translating it as "I can be healthy no matter how fat I am," which is definitely not true.

"Health At Every Size" was how it started, encouragement that you can improve your health despite not losing weight. For example, if you don't normally work out but decide to start, you're probably going to gain weight first - adding muscle faster than you lose fat.

"Healthy At Every Size" is the corrupted version you're describing.

> For example, if you don't normally work out but decide to start, you're probably going to gain weight first - adding muscle faster than you lose fat.

It takes at least a month to get your CNS firing correctly before your body can possibly build muscle in any significant way.

If you don’t work out and then you start, and you gain weight, you’re eating poorly, not gaining muscle.

BRI (Body Roundness Index, height/waist) seems like a much better metric than BMI and just as easy to measure: https://www.health.harvard.edu/staying-healthy/body-roundnes...

This is actually what I use.

I think that such “fat positivity” is not necessarily an organic grassroots phenomenon, rather it might be a consequence of the modern ad-driven internet. Celebrating personal expression, underdogs and minorities (and the obese can be slotted in alongside these) is something that advertisers love. Perceived negativity and judgement, on the other hand, could threaten advertiser relationships.

I never thought about it from this angle. I personally think celebrating body positivity is a good thing, but as it correlates to health, I think it can become harmful. IME there are a TON of "body positive" fat-focused influencers but I'm not sure a fat shaming influencer or even one that was criticizing the pro-fat movement would ever survive on social media, but maybe I'm wrong. I don't follow the young tiktok trends.

At least two influencers in the US criticize the HAES movement. And they're pretty just in their criticism (one is an ex-obese and is probably still overweight).

Yes, but a large component of worse health outcomes is due to bias on the part of healthcare workers.

Overweight people frequently have their problems ignored or downplayed, or given treatments for issues that they aren't experiencing, which leads to worse health outcomes.

I'm not denying that being overweight can be bad for one's health, just pointing out that when doctors provide worse treatment to a group of people that group has worse health outcomes and makes obesity more dangerous that it would be in a world without weight stigma.

Yea, my dad died of something similar - was morbidly obese among a lot of other problems towards the end of his life, they attributed a lot of those problems solely to his weight, but it turned out he had severe obstructive sleep apnea that was never treated. Had it been, I think his outcome would have been a little bit different. he was never even tested. We'd been telling him for years to get it looked at but his doctor convinced him the issue was weight.

Isn't obesity one of the contributors to sleep apnea?

It is a risk factor, but it is not 1:1. Lots of people have obstructive sleep apnea that are not obese. Sleep apnea can also contribute to weight gain.

You got me in the first half.

I actually thought you were preaching the same thing as the ones you are criticizing later on.

I agree that there is people with a high BMI that are quite healthy. So this is not a perfect indicator of health. Sure. But those people are a minority. At the scale of a country of ~346 millions people, having 3/4 of adults with a high BMI is a clear sign of an unhealthy population.

And, yes, unfortunately, some people decided that, because BMI doesn't work with a minority, we shouldn't care about it and, furthermore, shouldn't care about body composition.

Exactly this. Athletes are an outlier when it comes to BMI.

Furthermore, I reckon the majority of the people discussing BMI, as in these comments, would tend to be outliers, too, based solely on the fact they care/understand.

The majority of the population has no fucking clue, and can’t even read nutrition labels. And I am not blaming them. This stuff should be taught in school—basic nutrition education.

And even most athletes I personally know fall under what's considered a healthy BMI (< 25). Some sports require a body composition that pushes the boundary of it but as a general proxy of the health of millions in a population it's a pretty good one.

I will disagree here, athletes aren't the only one who can have a BMI > 25 and still be healthy, I'm at 26.2 now (down from 34) and my body fat is in the healthy range. BMI is actually just a poor indicator, hip/waist ration is as easy to calculate and is better imho.

Hip to waist is probably better but it has flaws as well. Especially in those who have lost a lot of weight and now have a lot of extra skin still there. No measure covers everything. You have to look at it in a holistic way. You can always use water tests to get lean body ratio if you’re super into it. Generally more important is how much is lean mass, how are your vital signs, what does your blood work show. Then one is getting closer to actually knowing how healthy someone is. A person 100lb overweight can be arguably healthier than someone who is 100lb lighter but has organ issues or high blood pressure or type 1 diabetes.

BMI is quite useful and fairly accurate for your average American, it probably covers 90% of us who engage in little to mediocre amounts of physical exercise. Everyone knows it’s for average people and not physical exercise enthusiasts, those people are into healthy enough to know they aren’t fat. BMI is an easy measure for doctors and patients to get a rough estimate. Your PCP will not tell you to lose weight if you show him your abs and pecs. Obviously this implies in-person doctors.

BMI, Both-Might-Indicate lots of muscles or fat stores. I can see how someone lugging lots of muscle mass around would want their own number - a BMI is either a credit score or a debt score, its absolute value means nothing. What if we did started to put a + or - in front of the number, if there was more muscle than fat being stored.

> What if we did started to put a + or - in front of the number

Not how a metric centred around 22.5 works.

Ok what if I used a different symbol with no mathematical alignment?

> what if I used a different symbol with no mathematical alignment?

A nonsense symbol?

The metrics you're looking for are body fat and muscle mass.

> I can see how someone lugging lots of muscle mass around would want their own number

Healthy people with high BMI are not how they are by accident, they don't care about their BMI because they know why it's high and they know it's not an issue

Yeah and this also affects like what...2% of people? It is indeed a non-issue that people keep marshalling in when this topic comes up.

exactly. the number of people who have "high BMI" due to muscle mass and general fitness is utterly trivial when compared to number who are straight up fat.

it's a nothingburger; whether you use BMI or Body Roundness or whatever, most USA-ians are fat as hell.

I don't think it is tricky at all. The number of people who are a bad fit for BMI is small percentage of the general population.

The tricky part is getting people to understand bell curves, standard deviations, and outliers when explaining why a policy is the way it is.

> a positive correlation with body fat, weight and health

I assume you mean a positive correlation between body fat and weight, and a negative correlation with either of these metrics to overall health?

Sure, body fat % is much better to use. Of course for many people BMI is perfectly accurate. Most obese people are not athletes after all.

BMI should just be modified with some kind of fitness dimension. Like take the traditional BMI and multiply it by your mile time / 9

BMI being based on the metric system, you should go for one's time on 1km ;)

This has been done for a long time. No sooner than 15 years ago many BMI calculators had options to adjust based on your average activity level.

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