Why BMI Is More Controversial Than You Think

BMI (body mass index) is one of the most controversial tools in health and fitness.
Some people say it’s outdated, inaccurate, and harmful. Others argue it’s still one of the most useful population health tools we have.

So… who’s right?

In this episode, we break down:
- where BMI came from
- what it was originally designed for
- what BMI actually measures
- whether BMI is useful for individuals
- why athletes and muscular people complicate the conversation
- how BMI relates to disease risk and mortality
- the biggest misconceptions about BMI
- weight stigma and the ethics of discussing body weight
- whether BMI should still be used in healthcare today

We also discuss how social media has shaped the BMI debate — and why many online conversations oversimplify both the science and the criticism.

This is not a “BMI is perfect” episode.
And it’s not a “BMI is meaningless” episode either.

As usual, we aim for nuance over outrage.

We hope you like it.

P.S., If you want to support us and would like monthly lifting workouts, you can join the Momentum by Sohee fitness app. http://momentumbysohee.com

If you are interested in fat loss science, you can purchase Ben's best-selling comprehensive fat loss book, Everything Fat Loss. http://geni.us/EverythingFatLoss

Transcript

SPEAKER_01 0:00

Today we are talking about one of the most argued about numbers in fitness, BMI or Body Mass Index.

SPEAKER_00 0:08

Now, BMI is definitely quite controversial. That a lot of people who think that it's not helpful, that it's outdated, that the number itself is harmful, and other people think that these criticisms are way, way overblown. The reality is there's a lot of nuance that tends to be missing from these conversations. For example, there was an article written by an MD where she said BMI is trash, full stop.

SPEAKER_01 0:35

That's fairly absolute, I think.

SPEAKER_00 0:37

Quite what's the saying? Painting with a broad brush. I had to look it up before this episode to make sure I was saying it right.

SPEAKER_01 0:44

I'm not even sure if that's the right saying.

SPEAKER_00 0:47

It's an overgeneralization. Okay. Right. And a quite extreme, one-sided take that is I think it's kind of unfair.

SPEAKER_01 0:57

I think it's fair to say that every single topic in health and fitness, but also in general, you are always going to get extremists of that point of view. And I think if everyone understands that, they should then realize that a lot of things that they will read about BMI are often either exaggerated or one-sided or not as impartial as we are going to be, hopefully. Yeah.

SPEAKER_00 1:23

I find that a lot of the claims or the views regarding BMI they tend to cherry pick a lot of the information to make their arguments. So we're gonna do the opposite of that, or at least we're gonna try to, anyway, with this episode.

SPEAKER_01 1:38

So we have had multiple requests to cover this topic. We are going to start with the origins of BMI, because if you know where it came from, I think a lot of the rest of it will then make more sense. But then we are going to go into a longer list of pros and cons.

SPEAKER_00 1:54

Yeah, specifically cons and then pros afterwards.

SPEAKER_01 1:58

I can't remember why we've done it last that way around. Oh, it might be because the cons list is is fairly lengthy.

SPEAKER_00 2:03

I I switched the order around. I thought it made more sense logically for the flow of the episode.

SPEAKER_01 2:07

A lot of people are aware of some of the cons, but we're going to go into some that most people are not aware of, and then we're going to go into some pros, which I guarantee most people are not aware of. So there will be people listening to this episode who are like, I'm dying to listen to that list. You have to listen to both because otherwise you're not doing the impartial one-sided view.

SPEAKER_00 2:28

First things first, what is BMI?

SPEAKER_01 2:31

So BMI or body mass index is a calculation based on your height and weight alone. If you know your height and you know your weight, you can calculate your body mass index. Unlike body fat percentage or waist to hip ratio or whatever is a very, very simple measurement.

SPEAKER_00 2:50

And the measurement is your weight in kilograms. But a lot of online calculators, you can do it in imperial units if you want.

SPEAKER_01 2:58

Right. I even looked at some of them and I was like, that's them, that's an American website.

SPEAKER_00 3:04

Yeah. So it's your weight in kilograms divided by your height in meters. So if you're 157 centimeters like me, it would be 1.5 centimet 1.57 meters squared. So meter. So weight over height squared. That's the calculation. But again, you don't need to know the formula because you can calculate this online. All these websites can do it for you.

SPEAKER_01 3:24

You just put in your height and weight, and then it will tell you a category. And I will put an image on the screen, but for those of you unaware, which I don't think will be many people, you will probably see a categorization chart where it spits out categories, and these change over time, and the terms used often change over time and depending on where you live, etc. But you might see terms like normal weight, underweight, overweight, obese, morbidly obese, or severely obese or whatever.

SPEAKER_00 3:52

Or I think they use class one, two, and three obesity.

SPEAKER_01 3:56

That's what I mean about terms changing. But in general, when people think about BMI, they probably think about things like normal weight, overweight, obese categories.

SPEAKER_00 4:05

And you might have heard something.

SPEAKER_01 4:06

Which I don't love, by the way. I'm not saying I love, I'm just telling you what you've probably seen.

SPEAKER_00 4:09

You might have heard people say, well, my BMI says I'm obese, stuff like that. That's kind of where those statements are come from. Uh question for you. What is, as of this morning, what is your BMI?

SPEAKER_01 4:19

I calculated this morning, my BMI is 25.3. So I am technically overweight. However, when I weighed myself yesterday, I weighed a tiny bit less and I was normal weight. That one pound made quite a significant difference.

SPEAKER_00 4:36

And that's something that we're gonna talk a little bit more about later on, is the problem with these kinds of classifications where you say you're this much different, or you're now we're gonna put you in a whole different category.

SPEAKER_01 4:47

I think very few people would look at me and say he embodies what I thought an quote unquote overweight person would look like. Yeah. And one of the biggest criticisms of BMI, which we'll go into later, is if someone is training a lot and they have more muscle mass, it can kind of artificially assume that they have a higher body fat percentage because they weigh more than you would expect based on that.

SPEAKER_00 5:11

And that is one of the biggest I think it's one of the most often said criticisms of BMI.

SPEAKER_01 5:16

Yes, but I think it's one of the least important criticisms. But it's the one that a lot of people, especially in the fitness industry, a lot of bodybuilders and fitness enthusiasts will be like, BMI is trash because here's my six-pack and I'm overweight, and therefore BMI is useless. But as far as the criticisms go, that's actually one of the more surface level, less relevant, less necessary kind of criticism.

SPEAKER_00 5:42

We'll talk more about that later, but real quick, did you say enthusiast? Is that how you pronounce it? Is that an English way? I say enthusiast. Oh.

SPEAKER_01 5:53

You say loads of things. I learned something new. You say loads of things weird. I do say enthusiastic.

SPEAKER_00 5:58

Am I the one saying it word or are you the one saying it weird? Definitely you.

SPEAKER_01 6:02

We both speak English, but you do the American. Uh like you say I say controversy.

SPEAKER_00 6:09

Controversy. Yeah. I say frustrating, and I notice you say frustrating.

SPEAKER_01 6:13

Frustrating. Frustrating. I don't know. I don't know.

SPEAKER_00 6:16

Anyway. I don't know how you pronounce it. Enthusiast. Okay.

SPEAKER_01 6:20

Yeah, enthusiasts.

SPEAKER_00 6:21

Next up, let's dive into without making it too dry, the history. Where did BMI come from? What is the history of BMI?

SPEAKER_01 6:28

So, rewind a couple of hundred years to the 1830s. There was a mathematician, statistician, and astronomer, apparently, called Adolphe Cetelet. And if you are French or Belgian listening to this, you are welcome to correct my pronunciation because I'm sure I've got it wrong. And originally it was termed the Ketelet Index. And he has a book at the time, and basically he looked at lots of people and he did stats, and that was it. There was no measurement of health here. It was just if you analyze people like height and weight, for example, what kind of trends would you see? So, some examples of trends from this book, which I I've put in there just for you to realise what he was kind of getting at. So here are some slightly more obscure trends. So, for example, taking the height and weight of 63 newborn boys and 56 newborn girls in a hospital and noticing boys tended to weigh a little more than girls. Yeah. A very benign thing to notice, but at some point you have to analyze people to pick up on trends like that.

SPEAKER_00 7:42

Right. And then he also noted that in the first seven days, a lot of newborns would initially lose weight before eventually getting it back, which is something that I feel like is quite common knowledge nowadays, but it's due to collecting data exactly like this that we know this to begin with. Which fun fact our baby did not lose weight within the first week. Not only was she well above average weight when she was born at eight pounds, 10 ounces, at her one-week pediatrician checkup, she had lost half and a half 0.5 ounces, which is basically nothing.

SPEAKER_01 8:16

Yeah.

SPEAKER_00 8:17

Medical staff were shocked.

SPEAKER_01 8:19

One of the things I actually like about this is if you realize that he was getting statistics on a kind of diverse, I say diverse, I'm talking about age. I'm not talking about race here.

SPEAKER_00 8:31

Very low-racially, very not diverse.

SPEAKER_01 8:33

Racially not diverse at all. But if you realize that he is doing things that are diverse from like an age perspective, it makes you realise that there are important needs for this. So for example, weighing babies is important because if they are not digesting well or if they're losing weight or if they're malnourished or whatever, these are things that can be used that aren't necessarily uh pathologized in the same way that overweight is for adults. Yeah. And a couple of other examples just to kind of throw them out there. So he also got data from local schools and orphan hospitals to establish average heights for boys and girls up to 20 years old.

SPEAKER_00 9:12

Also seems harmless.

SPEAKER_01 9:13

Pretty benign. Yeah. Uh between ages of five and fifteen, he noticed that boys grew 56 millimetres per year on average, but girls only grew 52 millimetres. Again, fairly kind of benign thing to pick up on. Then he did things like using data from colleges and hospitals, he averaged uh he established average heights and weights for men and women up to 80 years old. So noticing that above a certain age, people would stop growing. Weight gain was very rapid during puberty, but then slows down around age 25. And to quote, because this is where we kind of move into BMI, when man and woman, appreciate this is 200 years old now, when man and woman have attained their full development, they weigh almost exactly 20 times as much as at birth, and their stature is about three and one-fourth times greater than it was at the same period. New quote After the development of individuals of both sexes, the weight is almost as the square of the stature. And BMI, not BMI, but the Ketela index was born. So it's essentially an observation based on analyzing people. So if you take Sohi's height and weight, you take my height and weight, and you do it for 50 other people or whatever the number is, you'll be like, oh, the average is around here, and we notice growth charts over time and growth trends over time. Importantly, very important for you all to understand, there is nothing to do with health here. That was not the goal, it was not the purpose, it was not the implication. He was not measuring health, he was literally just measuring things like height and weight and other things that are in the book. But let's go with that.

SPEAKER_00 10:57

Additional detail that a lot of people will bring up is that the population he studied was white European people.

SPEAKER_01 11:04

Right. And if you have heard that BMI is racist, this is uh This is where it stems from. A valuable criticism for where it stems from. Because if you analyze a local group of people and then you apply those numbers to people from other countries, races, ethnicities, it can get pretty messy pretty quickly. And we will go into that in more detail later.

SPEAKER_00 11:27

Yeah. Uh another fun fact. Well, it's not very fun, but it's an interesting thing.

SPEAKER_01 11:34

We're a health and fitness podcast. We're playing it fast and loose on the words.

SPEAKER_00 11:37

Okay, anyway.

SPEAKER_01 11:39

So You can't go from fun fact to morbid facts. Those those are mutually exclusive, surely.

SPEAKER_00 11:44

This is also where the um the eugenics movement was stemmed from this. Super fun fact. Sorry, not it's definitely not fun. We are not laughing at the fact that eugenics happened exists.

SPEAKER_01 11:57

Super fun facts.

SPEAKER_00 11:58

Um, but you know, eugenics is where you are trying to promote an ideal, I say having a quotes ideal human and try to kind of refine what the human race looks like, and you you take the people of quote unquote ideal body weight, and then you're like, okay, these are the people that we want breeding together and so on and so forth.

SPEAKER_01 12:17

Yeah. So kind of as a side note to that, that was not the same guy.

SPEAKER_00 12:23

No, that was someone else. That was Francis Galton. Yes, it was Francis Galton. Okay.

SPEAKER_01 12:31

The reason that I'm just kind of putting that in there. That happened later on. If you said, Oh, I've established these kind of average height and weight charts, and then I come along and look at them and go, oh, I'm gonna burn everyone that's in the red area, you can't be like, that's not I didn't do that. Right. That's not a criticism of my Ketelay index. It's just this fucking weirdos come along and decide to do that. So you know, take take that with a pinch of salt, be aware of how it is used, but that doesn't necessarily mean it was why it was originally created.

SPEAKER_00 13:00

Right, but that's also partly why people find it problematic now.

SPEAKER_01 13:04

Yeah.

SPEAKER_00 13:05

Because of its origins, exactly, exactly the stuff like this. But also it was eventually used for life insurance, which you'll talk more about.

SPEAKER_01 13:11

Yeah, so I have some notes on my iPad here, mainly because historically or doing history kind of lessons, I personally dislike because I can't go back in time and verify things for myself. So I'm always relying on research papers, and because I'm relying on research papers, I like to quote things. So, for example, and I'll put images on the screen if you're watching. So between 1885 and 1908, anthropometric like body measurements were taken from life insurance companies, which were then allowed to be cross-referenced with mortality rates. So if you're a life insurance company and you insure however many thousand people, you could see who dies younger, essentially. And that is where BMI kind of evolves into because now we are not just taking height and weight, we are taking height and weight and cross-referencing it with some marker of health, in this case, mortality. When did people die? Then, by 1937, Metropolitan Life Insurance Company partnered with a statistician and using data of 4 million participants, established the ideal body weight. That's nearly as far as the history lesson goes. I'm not going to go into more detail with life insurance companies, although it evolves a lot. But the whole thing you need to remember here is this is where ideal body weight came from. So if you look at four million people and say, well, based on their height and weight, these people lived longest. Yeah. Therefore, people outside of that range aren't part of the ideal body weight. And that is where overweight, underweight kind of comes in and stems from.

SPEAKER_00 14:46

Yeah, yeah. And then surface level, if you think about that, you think, okay, that makes sense. Yeah, it does make sense. Oh, yeah, yeah. And obviously, as you don't analyze deeper than that, so became kind of widely accepted.

SPEAKER_01 14:58

This is going to be a super loose comparison, and I don't want anyone to ruffle their feather feathers over it. But for example, if a car insurance company said, Oh, we notice that 17-year-old men get into more accidents, that is just something that they can notice from data. Or, for example, home insurance, if they notice that people who live in certain areas are more susceptible to fires or flooding or whatever, that is essentially how you can collect data. It's just whether you are using it for malicious purposes, which is obviously what we'll get into. But just keep in mind that analyzing data and coming up with trends isn't necessarily a bad thing in itself. Yeah.

SPEAKER_00 15:37

I also want to bring up an actual interesting fact, an actual fun fact, which I think is more innocuous. Less eugenic. Yes, okay. This is according to a research paper, okay? And as we talked about beforehand, we weren't able to um verify, verify, so take it with a grain of salt. But according to this one paper, they had first originally identified normal weight range as BMI of 19 to 24. Okay. From there, there was another person who came along and said, Okay, yeah, but 20 to 25 is easier to remember. So let's make it that. Let's make that the normal range. So let's just shift it a bit. Let's shift it to something that people can remember more easily, which seems quite arbitrary, but also reminds me of anyone who's watched the our previous episode, 95% of diets fail.

SPEAKER_01 16:19

Oh, yeah.

SPEAKER_00 16:20

The number of people who have said, well, 95%, even though it's not accurate, it's easy to remember. Therefore, we're gonna go with that. So kind of reminiscent.

SPEAKER_01 16:29

20 to 25 is easy to remember. I like round numbers. The same reason on if I'm doing volume on a TV, I will always stop at say 20 or 25, and you'll do 19 and it bothers me.

SPEAKER_00 16:39

I'm like, no, but I want to find the actual right volume, whereas you might like the inconsistent.

SPEAKER_01 16:43

I need to round up. Yeah. So history lesson. If we fast forward, we're going to go right to 1972 with a very famous researcher called Ansel Keys, which I won't go into more detail actually. That's boring. Anyway, so he kind of validated this theory. So if you have height and weight measurements, at the moment you have no actual measure of body fatness, and that is kind of where he came in. So he tested this, and there are other measures or other predictors of body composition. It isn't just body mass index, there are other ones that you can test, which we don't need to go into now. And if he looked at skin fold measurements, for example, he can then cross-reference and see which of these is the best predictive equation. And at the time, this index, which then changed into the quote unquote body mass index, was the best one. So this is how the initial height and weight predictor then was validated for is it a good predictor of actual body composition or actual body fat percentage?

SPEAKER_00 17:48

Yeah. And he also found that even though he himself said that towards especially the middle ranges, the normal ranges, it was not super accurate at predicting or linking to body fat when you the further away you got, so if you had a very high BMI or a very low BMI, it was better at predicting you would then have higher body fat percentage or a lower body fat percentage.

unknown 18:11

Yes.

SPEAKER_00 18:12

Accuracy would increase the further away you got from normal BMI, middle BMI.

SPEAKER_01 18:16

So, yeah, generally speaking, if someone has a super, super low BMI, they are probably unlikely to have a lot of body fat. If someone has a super, super high BMI, they are probably unlikely to not have much body fat. It's very rare that huge, huge bodybuilders will have a BMI of say 40 plus, for example. Right. Uh but as a quote here, because I think this is important, so this is essentially the founder of BMI, or at least how BMI is known now. Yeah. His own quote. In much of the literature, especially in discussions of clinical problems and in reports from the life insurance industry, relative weight is taken as a measure of obesity or fatness, in spite of repeated demonstrations and warnings of the serious errors arising from that confusion. So we kind of went into this thinking there are definitely limitations with this kind of approach. Let's validate it, let's test it. And that is where BMI was born, 1972.

unknown 19:12

Yeah.

SPEAKER_00 19:13

And it's been used over the decades to observe trends in especially obesity levels across in the US population. We're gonna pop on a graph.

SPEAKER_01 19:22

Can I interrupt super briefly, super, super briefly? So because we said that Adolf Kettele used a very, very narrow uh population of people, this was slightly less narrow. So when people say it's very racist, because if you're only studying people from Brussels, for example, and extrapolating it elsewhere, this was less narrow. So he looked at data of over over 7,000 men. Note men only, which is obviously still problematic, but over 7,000 men from 12 different cohorts, including Italy, Japan, South Africa, Finland, and America.

SPEAKER_00 19:57

That's definitely an improvement.

SPEAKER_01 19:58

So it's an improvement, but it is still men, which of course is still a limitation you need to be aware of. Back to you. Okay. Thanks.

SPEAKER_00 20:05

Yes. Pop on the graph. Graph on the screen. Basically, you can see over time, over the decades, the 60s, 70s, and so on, obesity. We're using once again, we're using BMI as a reflection of obesity, but we have BMI trending upwards over over the decades across different age groups between men and women. And then they use this population level data to say, oh, we're having uh obesity problem that's getting worse and worse and worse.

SPEAKER_01 20:32

Yeah, I want to just explain something here because I really need everyone to understand this because I think it's actually very basic. But imagine that you are a researcher and you are trying to collect data from people. So, for example, let's say you are looking at we want to know which dietary patterns make people live longer, for example. You need to get a certain amount of data from people to create research, and you will ask people's uh age, for example, whether they smoke, whether they drink. If you ask people's weight in isolation, that is fairly fucking useless. If you asked someone's weight now blindly and you've never met them, and they say, Oh, I weigh 200 pounds, that means nothing. But if they say I weigh 200 pounds and I'm four foot tall, or I weigh 200 pounds, did I say 200? Still 200? Yeah, or I weigh 200 pounds and I'm eight foot tall.

SPEAKER_00 21:28

Oh gosh, yeah.

SPEAKER_01 21:30

Having having height then puts it into context. So if you're doing research of lots and lots of people, using height and weight or asking for height and weight is something that makes sense, and therefore, whether you like it or not, you have indices based on height and weight. Whether you want to use BMI or not is separate, but you can't ask for things like body fat percentage, whereas you can ask for height and weight because everyone knows it. So it is very, very common for research. To use BMI or use heightened weight because that is essentially the best data that they can get if they're asking thousands and thousands of people for information. Hence, when you're looking at trends in research papers, they will often say, we find that people with a BMI between 20 and 25 tended to live a little bit longer than people with a BMI over 35 or BMI under 19 or whatever it is. That is why they have come to those conclusions. It's because that's kind of the only re data that they can base their research on.

SPEAKER_00 22:34

Yeah, especially to get the end, the sample size that they they're getting, usually tens of thousands, sometimes more. It's way more accessible to collect those two pieces of information from that many people.

SPEAKER_01 22:45

Yeah, and you need to know that. We will recap towards the end. But this is a good thing to know.

SPEAKER_00 22:50

Yeah. Let's dive into what are the cons of BMI? And this is this is where this is the stuff that most of you will be familiar with, at least some of the points that we bring up.

SPEAKER_01 22:58

Firstly, it is not great on an individual level. That is not really so how it's supposed to be used. So if you understand why researchers use it when they're looking at lots and lots and lots of people, that doesn't mean that it should be applied to you as an individual strictly. So as an example, if someone else weighs the same as me at the same height, so 180 pounds-ish, uh, a smidge under six foot, I'm not quite allowed to round up, a smidge under six foot, they might smoke, they might drink, they might take party drugs, they might not exercise, they might have a worse diet, they might have a worse lifestyle than me, but we still have the same BMI. So you can't accurately predict people's health status based on BMI alone. So whilst you can look at trends of lots and lots of people, you should not look at someone and say, your BM BMI is this. That means you are immediately unhealthy because you will trip over. Yeah.

SPEAKER_00 23:58

Which unfortunately, unfortunately is a mistake that a lot of people make, including did you merge unfortunately and importantly?

SPEAKER_01 24:03

I think so. I I liked it.

SPEAKER_00 24:06

Which unfortunately does happen even in a medical setting, which is I think I will say that I I think this is a big part of why a lot of people have such strong reactions against not only BMI, but body weight measurements in general. It's if you personally have had a not pleasant experience in terms of people treat you differently, or maybe your doctor was dismissive of your health concerns because they made assumptions based off your bi your body weight or your BMI, I understand why there is such this strong reaction against it.

SPEAKER_01 24:39

And I want to double down on that because I think that is probably the most important take-home message from this whole video, is regardless of what the research says on BMI, regardless of whether it's valid in what percentage of people or how accurately it predicts body composition in what percentage of people, ultimately the way it's used in real life is the reason that so many people get upset by it. So if you were a client and you came to me and I said, I'll step on the scale, well, you're obese. That is very valid for people to be pissed off. Yeah. That isn't necessarily a problem with the BMI number itself as much as how it is then implemented. So if you stood on the scale, if I was your personal trainer and you came in and I said, we'd just like to get your height and weight, get some initial stats if you're comfortable with that. If I said your BMI is this number, most people would go, okay. But if I say your BMI is this number, and then I look at the chart and go, mm, you're obese, that is when people tend to get more upset because it's more of a moral judgment rather than just what the number is. Right. Same with body fat percentages. When I used to do body fat percentages with clients, not all clients, clients have felt comfortable doing it and clients have wanted to track their body composition. If I said your body fat percentage is 19 to pick out a random number, almost always they would say, Is that good? Yeah. Because without the charts they don't know how to interpret it. Right. So the number the number itself is fairly benign, whereas when you cross-reference it with a chart with a big red area saying overweight or obese, that is when people are gonna feel pretty shitty. Yeah.

SPEAKER_00 26:20

And I think the categories and there's papers written on this, people argue it's not the number itself that's the problem, it's the way that we then categorize, oh, this number puts you in the overweight category or the obese category. And it's the negative connotations associated with these terms overweight and obese that I think people have take issue with oftentimes. And then then obviously that's linked to weight stigma and whatnot, and there's a whole trickle-down effect from there.

SPEAKER_01 26:49

Yeah, and we can come back to that, yeah. But next con BMI does not actually tell you anything about body composition, specifically fat storage patterns. Right. So if you had five people with exactly the same BMI, they are going to have different body fat percentages. On top of that, they are going to have different fat storage patterns, which can then infer a different health risk. So if two people have a BMI of 25, but one person has more visceral fat proportionately than the other, that might be a higher risk factor in itself, even though they both have the same BMI and the same body fat percentage. Yeah. So BMI is kind of guessing how much body fat you have, but it's not doing a very good job and it's not able at all to tell you about fat storage patterns, which is a huge problem.

SPEAKER_00 27:43

Going back to you as an example, you're someone who has a much higher than average amount of muscle mass. But definitely or or lower, low much lower than much lower than average levels of body fat. That's for sure. Yeah. And BMI alone, you wouldn't know that. So there, yeah, as you were saying earlier, there's someone who can be exact same height, exact same weight as you, but put you side by side. You can look body composition-wise, you can look very, very different. And they could, as you said, have much, much higher levels of visceral body fat, which we know is linked to negative health outcomes.

SPEAKER_01 28:16

And this is why some researchers, scientists, obesity, obesity specialists, however you want to phrase it, this is why they will often recommend using a separate measurement to kind of cross-reference or further validate that BMI score. For example, if I have a BMI of a smidge over 25 today or a smidge under 25 yesterday, which is kind of funny, and someone else has the same BMI as me, they might say, okay, let's also do a waist measurement, because that will give us a crude-ish indicator of visceral fat. So they might say, let's take a waist measurement or let's take a waist and hip measurement, because that will give us an indicator of abdominal fat, for example.

SPEAKER_00 29:02

Yeah. Next con is that it doesn't really translate well to different populations. So one example we used was with athletes. So I would consider, let's say you were you're an athlete or someone who's a professional athlete, they typically are going to have um higher than level, higher than average levels of lean body mass. Now, a lot of people, as we said, do use this as one of the criticisms is that, well, it doesn't tell you how much lean body mass people have, which is true. But the reality is, is that those people account for a very, very small minority of the population as a whole.

SPEAKER_01 29:33

Yeah. So in the fitness industry, I think it's almost a bragging right in the bodybuilding world for people to go, look, I'm overweight, or look, I'm obese because I have so much muscle. But in reality, I have been exercising for 20 plus years. I am a smidge into the overweight category. It isn't until you get to bodybuilders who are often taking a lot of anabolics and performance-enhancing drugs that they tend to super supersede that. Generally speaking, the percentage of people who have bodybuilded, bodybuilt, I don't know. Body bald.

SPEAKER_00 30:10

I don't know.

SPEAKER_01 30:11

Whatever. Who have built their bodies into such incredible muscularity that they are in a class two, three obesity is very, very slim.

SPEAKER_00 30:24

Yeah. And then you also have differences by uh sex as well as by ethnicity. Yes. And by age.

SPEAKER_01 30:31

Yeah. So for example, there are research papers that will say if you look at black women and white women with the same BMI, black women often have more lean body mass than white women. But if you were just looking at BMI alone, you wouldn't necessarily take that into account. And this is where the racism thing that we started earlier, we mentioned earlier, becomes more prominent. Because if you study a group of white people and say anything above this is overweight and we think that you have more body fat, and then you apply that to black people, for example. And if it doesn't translate well, you are getting into very, very dangerous territory where you are applying the wrong brush stroke to the wrong population. Yeah, and there's there's also other research. So, for example, uh, if you compare Asian Indian and African American people with the same BMI, uh African American people might have a lower body fat percentage. Yeah. Same, same as what I just said, but looking at a different comparator.

SPEAKER_00 31:31

Another criticism or con, which you've touched on at the beginning of the con section, is that it does not predict individual health status. So the example that we like to use is that you have a chronic illness. So you have Crohn's disease. We have a whole episode on this, you can go back and listen to it from before. Or if someone is super, super thin but they have cancer, or if they are a chronic smoker or alcohol drinker, that would not be reflected in BMI. Or if even if they have the ideal or normal, normal BMI, quote unquote, but they have something, they have a health a con like a condition, a medical something, an illness.

SPEAKER_01 32:08

Average life expectancy for people with Crohn's disease tends to be a few years lower than people without Crohn's disease. Obviously, BMI doesn't capture that. Fun fact, I might die earlier.

SPEAKER_00 32:20

Yeah, I don't really like to think about that.

SPEAKER_01 32:21

You said fun fact, I'm just going with the fun fact. Only a few years, it's not like decades or whatever. But there is also research that I have mentioned before in my first book. So if you look at Call What? I'm not even doing that because it's gonna sound intentional. Fine, everything fat loss. But near the beginning. So if you look at people in BMI groups and you look at when they die, so you cross-reference those two, if you break it into subgroups, you will find that healthy behaviors can intercept the BMI to mortality relationship. So someone with a higher BMI might have an elevated risk if you only go on those two. But if they consume more servings of fruits and vegetables, if they are exercising, if they don't smoke, if they don't drink alcohol, all of those can bring down their mortality risk, which is not captured in BMI alone. So if you go into the doctor and they say, well, you are unhealthy because your BMI is 25.1, which is what mine is or close to now, but they haven't asked me anything about my lifestyle, it's making a very snapshot judgment based solely on your health, based solely on your weight, rather, right, to infer your health, rather than actually asking you about your health. Right. And that is the right.

SPEAKER_00 33:41

And and and and I I would argue that when you think about it, it's not actually that example, it's not the BMI number itself that is the issue, it's the people who then take that value and what they do with that number and how they treat you as a result of it. That's the problem. Kind of similar to saying, well, it's not the scale weight that's the problem that you hate, it's your interpretation of what you think the scale weight signifies. That's the issue. That's that's kind of the parallel that I think of in my head. But it's still a problematic.

SPEAKER_01 34:08

Which nicely, I think, brings us on to the next con, which is when BMI is used to penalize individuals. Yes. So for example, if I do I'm actually supposed to do life insurance now. Now we have a baby. I'm supposed to do life insurance because if I die, it'd be nice if you get some cash. And they will ask me for my height and weight. And if they look at my height and weight and say, well, actually, he's 25.3 or whatever it was today, that might mean that I have to pay a slightly higher premium than if I was 24.9. I haven't looked into this to know if those are the numbers, but if I'm slightly above the threshold and I'm in the overweight category this morning, in theory, if I did my paperwork yesterday, that could influence the cost of my life insurance based again solely on height and weight. Yeah. And again, there are other examples like drugs, uh cutoff or surgeries, for example. You qualify for this procedure if you get to a certain weight. Yeah. And I don't want to go into that because a medical medical professional sh would do a much better job going into that. But you can see why this becomes a slippery slope. If you need medication or you need surgery or something that could be life-saving, they say, well, we can't give it to you at the moment based solely on your BMI. Yeah. You understand why it's a painful topic for a lot of people because it can be used to discriminate against them.

SPEAKER_00 35:30

Yeah. The last con that we're going to mention here is actually very related to the point that you've recently brought up, so it's a nice segue into this, is that classifying people as obese, so putting that categorical label on them, can have quite negative connotations. There's a couple studies that demonstrate this. The first one has to do with um, this was to not surprise anyone. People don't like the terms or the labels fat and obese in general, which makes sense.

SPEAKER_01 35:57

There's so there's actually slightly contradictory research literature here, but in general, I think it's okay.

SPEAKER_00 36:02

I think it's people are trying to change that in recent years where a lot of people are. Especially in the body positives. Yes, and they're saying actually fat is not an insult, it's a neutral descriptive term, whatever, blah blah blah blah. Regardless, in the study, they found that people in general did not like the terms fat and obese. And they also found that if they felt like their um doctor was going to make them feel bad about their weight, one in five people would say there if that's gonna be the case, I would rather avoid medical care, which honestly I I understand.

SPEAKER_01 36:29

Yeah. Yeah. If you're avoiding medical care because your doctor makes you feel like shit, that is a huge issue. And this is a great example of how BMI kind of gets weaponized, maybe, is the you see what I'm getting at? Yeah. I don't know if it's the right word, but I get it, yeah. Yeah, it it becomes an issue, and people are penalized for their weight, and therefore they don't go back to the doctor, and that is a whole can of worms in itself. Another research paper that I like is they took a group of people and they gave them their classification: normal weight, overweight, underweight, but this one had a twist because they lied essentially. So they would misclassify people on purpose. And the reason you do this is because uh one, if people have more body fat or less body fat, that in itself could change how they feel about themselves, but you need to intercept that with how you are describing them. So if you take someone who's normal weight and say, oh, actually you are overweight, what happens to how they feel? And this study found that if you classified people as overweight, they had an increased depression score and a decrease in self-esteem. And this isn't based on their weight status itself, their actual weight status, it's based on their perceived weight status, which is a direct example of how a not even the BMI number, but the score on the wall of you are overweight, you are obese, can immediately make people feel like shit. Yeah. And that's different to the number itself. It's how that number is then used.

SPEAKER_00 38:06

Yeah, which then brings us back to the question of is the actual categorization of this range is gonna be this label, this range is this label, is that ultimately helpful? Now I understand why they use the terms overweight obese. It's easier to understand than you're in weight range one, two, or three, obviously it's gonna be make more sense. But at the same time, there's all this heavy connotation associated with them that you cannot unlink from that.

SPEAKER_01 38:36

Yeah, some immediate judgments. Yeah.

SPEAKER_00 38:38

For example, and also the other point too is if you're if your BMI is 25.1, so you're borderline quote unquote overweight, you're still classified as overweight in the same way that someone with a BMI of 29.9 is classified as overweight, even though your body weights can vary quite a bit. So you're still both within the overweight category. Is that fair? I don't know.

SPEAKER_01 39:01

Let's probably not shift onto BMI pros, which is admittedly a much shorter list.

SPEAKER_00 39:06

It's shorter, but you'll you'll understand when we talk about it, you will understand why BMI has persisted to this day, and why, at least I think people haven't found a better method, necessarily.

SPEAKER_01 39:23

Yeah.

SPEAKER_00 39:24

Okay.

SPEAKER_01 39:25

First and foremost, it is inexpensive and it is easy to implement. So let's pretend BMI didn't exist and you were a researcher and you were trying to get some kind of body composition data of thousands of people for your nutrition study. Like, we want to see whether red meat causes heart disease. So we're going to look at diets of 10,000 people. You need some marker of body composition to know whether that is a variable. What do you do if BMI doesn't exist? You can ask for their height, you can ask for their weight, you can't ask for their body fat percentage because how many people can accurately do this? So, as an example, uh, I have been on courses where people were taking body composition of each other using skinfold calipers. So imagine a group of highly interested personal trainers and strength coaches, not just we've just qualified, but we've been in the industry years, we love this, and we're taking each other's body fat percentage using skinfold calipers. And I promise you that if four people came up to you and measured your super iliac, for example, or your umbilical next to your belly button, you would normally get different measurements every single time. Sometimes only a little bit, but I've had measurements where one guy was like, Oh, this is 20 millimeters, and the guy that did it before was like this is eight millimeters. You there isn't an easy way to take people's body fat percentage, which is free and accurate. Yeah. What would you do? You can't use skinfold because most people don't have calipers, most people don't know how to use them. You can't use DEXA scans because they're hard to find, they're expensive, they take time. You can't use underwater weighing for the same reasons as DEXA scans.

SPEAKER_00 41:11

Every method you've listed is either inaccessible or there's so much margin of use there's so much user error. And even with even if you say, okay, well, you can use those scales that tell you your body fat, those are wildly inaccurate.

SPEAKER_01 41:23

Yeah, so like bioelectrical impedance analysis, the BIA scales that you stand on, sometimes the ones you hold with your hand, they pass a little electrical current through you and they predict your body fat percentage based on your body density, and the margin of error on them is huge. Yeah. Number one, again, if you are looking at data of thousands of people, you can't ask them all to find a a device. If you did that, you'd have to use the same device for everyone, and you would have to factor in such a wide margin of error that it would be a limitation in the study itself. So basically, BMI wins by default, yeah, because there is no better way.

SPEAKER_00 42:00

There is no despite all the criticisms, all the cons, which are very valid, were like, okay, but what other better way is there? So I actually had a very small, and we can fly for this quickly because the criticisms are going to be the same of alternative methods to BMI that researchers and other people have proposed. Um, but we can also talk about why they haven't really picked up. So the first one is waist circumference, which personally I I when I used to work with a lot more coaching clients for their fat loss goals and whatnot, I always I liked to collect their their waist circumference because it is actually a really great way to capture body composition a lot more than body weight by itself. So I used to do the same thing. Yeah, it captures body comp quite well, especially body fat changes, right? Problem with that is main thing is that people are very bad at taking accurate waist circumference measurements.

SPEAKER_01 42:51

I was gonna say that waist circumference sounds easy, but it isn't easy because number one, people suck in, even subconsciously. Yeah. The number of times they pull tighter, yeah. Or the tape drops down slightly at the back.

SPEAKER_00 43:04

Yeah, it's not straight, or they they it's a bit higher one time or a bit lower another time. There's so much variability.

SPEAKER_01 43:10

I used to say, let's go around the belly button and we keep the tape measure exactly flat the whole way around. That way it doesn't matter if their pelvis is tilted one way or another, for example. But even so, uh a measurement could change by a couple of inches, just whether someone's like fully relaxed. I would always say relax, breathe in, breathe out, relax. And I would always say, Are you fully relaxed? And almost always it would then move another inch or so, just because subconsciously, when people yeah, when people around your stomach, yeah, like I'm permanently semi-flexed anyway, it's basic basically the same thing.

SPEAKER_00 43:44

It's like it's like when you have um imaginary lat syndrome, but it's with your waist.

SPEAKER_01 43:49

It's like when you're walking walking past a swimming pool on holiday. Sure, yeah. Like how many men are really 100% relaxed? Not not not 80%, not gripping. There be uh just a little bit too hard or whatever, fully 100% relaxed. Probably not. And that's waist measurement. Waist measurement is a tape measure which is very cheap. You could do it at home, it's still not reliable.

SPEAKER_00 44:11

Yeah. On a related note, there's also what's some something called the body roundness index, which I'm not sure how much I like that name, body roundness index, which uses your waist circumference, maybe also your hip circumference, plus your height, and it does not take into account your weight. So for that reason, people are like, oh, this is nice. We're looking into body fat percentages. But again, we go back to the same exact problem with okay, but how accurate are you gonna be with measuring your waist and your hip circumference? Yeah. So for that reason, it's once again not gonna be that accurate. Um, but there is if we did we they did find that there is a nice U-shaped association between this value, the body aroundness index, and all cause mortality risk. So they're like, okay, in theory, it can be great, but in execution, when we try to do this in real life, it falls apart.

SPEAKER_01 44:59

Yeah.

SPEAKER_00 45:00

So we try other methods, you can propose whatever you like.

SPEAKER_01 45:04

Ultimately BMI still slightly.

SPEAKER_00 45:07

Is there anything better than BMI right now, especially for a population level?

SPEAKER_01 45:11

Yeah.

SPEAKER_00 45:12

Not really.

SPEAKER_01 45:13

Next pro is if you look at population data of thousands, hundreds of thousands, millions of people, BMI does often correlate with certain health risks, such as mortality. So I can put some images on the screen, but say from a meta-analysis where it looks at lots of lots of different research papers, it will often find that people with a much, much higher BMI tend to die earlier. And also people with a very, very low BMI tend to die earlier. That bit often surprises people because they often think overweight, obese bad, underweight less bad. And a lot of people idealize being super thin, especially at the moment. But as an example, if you are suffering with a disease or a muscle wasting condition, uh, when I was in the midst of my Crohn's disease and I lost 50 pounds, I went down to 132 pounds. If I had died then, that would have been an example of how there's a an elevated risk with very, very low uh BMI status. So if you look at research papers, there are often elevated risks at the high end on BMI and the low end of BMI. Now that does change based on subgroup. So for example, if you look at if you break it into subgroups like people with cardiovascular disease, or if you look at Asian people versus white people, or older people versus younger people, or smokers or non-smokers, or whatever, that can change the trajectory of the curve. But there is still a correlation between BMI and mortality risk and certain other health risks. So it is still sometimes a valuable tool to use. Yeah.

SPEAKER_00 46:55

Final pro, very quick one. BMI can predict some health risks quite well, such as undernourishment.

SPEAKER_01 47:04

Yeah. So for example, let's remove doing it to adults, let's remove telling people what weight category they're in, let's remove all of the emotional baggage that that comes with. Let's say our baby, they can look at weight charts and they might say, hmm we are worried that your baby is not getting enough food. Yeah. Um, or certain diseases. So if someone's weight drops off the low end of a BMI chart, that might be cause for concern on if there are underlying conditions, for example. So, yes, there's a lot of emotional, emotionally charged topics when it's used from a we're going to penalize you for having more body fat, which is often primarily how it's used, but it is still very useful for uh identifying potential issues. Yeah. So are babies getting enough food, for example, are babies matching their growth chart. When they were doing ultrasound on our baby when you were pregnant, they would still cross-reference it to average reference points.

SPEAKER_00 48:05

She's in the 83rd percentile. Now she's in the 91st percentile.

SPEAKER_01 48:08

Even things like head circumference or abdominal circumference or whatever, those aren't BMI, obviously, but they are still comparing it to averages to potentially identify issues such as certain diseases or deformities or whatever. That is an example of how cross-referencing things to an average can sometimes raise flags, which might then need an intervention, which is obviously a very, very important thing, which often isn't how BMI is used, admittedly. Unfortunately, yeah. It is important.

SPEAKER_00 48:40

Yeah. With all that said, what are some of the key takeaways for you? First point is that BMI is one data point. It should not be interpreted or taken in isolation. That does mean that if you have a doctor or healthcare provider who is making assumptions off your body weight or BMI alone to then make assumptions, incorrect assumptions based on about your health or dismissing you, I'm gonna go as far as to say they are wrong. They are in the wrong for doing that.

SPEAKER_01 49:06

There is a a quote that I pulled out from the American Medical Association, if you want to read it, which helps, I think, really drive that point home.

SPEAKER_00 49:16

Yeah. Uh the AMA suggests that it, it being BMI, be used in conjunction with other valid measures of risk, such as, but not limited to, measurements of visceral fat, body adiposity index, body composition, relative fat mass, weight circumference, and genetics slash metabolic factor. So basically take other factors into account, put it into the proper context, which is what they're saying.

SPEAKER_01 49:39

Kind of what you would hope. Rather than a doctor saying your BMI is 28, therefore you are unhealthy, it would be more along the lines of, oh, your BMI is 28. And we have noticed that your blood pressure is high. That is actually measuring a proper health marker rather than assuming you have ill health based on body weight alone.

SPEAKER_00 50:00

Yeah. For example, for you, we can say, well, your BMI technically puts you in the overweight category, but given how much muscle you have, your body fat percentage, the fact that you exercise, etc., that's not something that we're actually concerned about. Or something like that.

SPEAKER_01 50:12

Even if I had done this yesterday when my BMI was 24.9, a medical professional might say, well, your BMI is technically normal, but your inflammatory markers are higher than normal, which is very common for me because of my Crohn's disease. Your blood markers are often out of whack because they have been historically. That is again an example of how you should cross-reference it with more important clinical points.

SPEAKER_00 50:35

Right. Tell us about the Lancet review from last year that's very related to this.

SPEAKER_01 50:39

So this is very, very important. There was a big review paper from last year where they interviewed dozens of obesity experts and they were debating and trying to agree upon the definition of obesity. So people will argue whether obesity is a disease or not, and that's a kind of separate thing. We don't have to go into it now. But one of the important things that they agreed upon is you should not rely on BMI in isolation, and you should then cross-reference it with other things. And this is a literally dozens of experts getting together, so it's fairly authoritative. And an important quote from here is 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.

SPEAKER_00 51:34

We can't emphasize that enough, and yet I know that people are going to continue doing that.

SPEAKER_01 51:38

That is essentially, if if we could summarize the entire episode, that would probably be the the sentence that people need to take away. On a population level, BMI is useful, it wins by default, but it is often used on an individual level to make people feel shit.

SPEAKER_00 51:56

It reminds me of that statement that I've said many times. You cannot infer someone's health status based on their body size alone. That's but kind of I would say they're basically one and the same. Yeah. Wouldn't you? Yeah. Yeah. Um, but ultimately, despite all of its limitations, we should not be dismissing BMI completely because it still has utility. Again, from a big picture zooming out aerial view population level, it is still useful for that.

SPEAKER_01 52:23

I actually think it's kind of a red flag when people say BMI is trash with no further context, because for you to be fully informed as a listener, consumer, however you want to phrase it, you need to know pros and cons. Everything has pros and cons. Even if the cons list is very, very big and the pros list is very, very small. If someone says it's trash, you have to throw it out, that is not giving you the full picture, and we think you deserve better. So I think it's very, very important that you understand why it is still used and it will continu will still continue to be used, but it's okay to acknowledge that and still all unanimously agree that the biggest problem with it is how it is misused to penalize people, make people feel like shit, and all the other ramifications of the things that we've discussed in this episode.

SPEAKER_00 53:17

I actually think that a lot, if we could address the weight stigma part uh that's so tightly linked with BMI, the overweight and obese categories, a lot of people's gripes with BMI would go away. Unfortunately, that's probably never gonna happen in in terms of weight stigma never being a thing anymore. Yeah. Um so that's gonna be something that we're always gonna have to address.

SPEAKER_01 53:38

If everyone who went into a doctor's office had their weight, if they had their weight taken, if they had their weight taken and it was just written down and that was the end, yeah, the whole topic of BMI would probably fall apart because most people wouldn't care about it anymore. Yeah. It's just the fact that for decades it has been used to paint people with the same brush. You are unhealthy because your BMI is 28, therefore you need to diet, you are lazy, all of the connotations that come with it. Yeah. And that's the issue.

SPEAKER_00 54:09

Part for the course, for us, BMI is not all good, BMI is not all bad, as with many other topics, we don't take a very extreme stance. But research says it has its pros, it has gone, it's here to stay. So let's understand its utility while recognizing its many limitations.

SPEAKER_01 54:26

What I would actually love to hear is if you have listened to this episode, I like this because I like getting feedback. If you've listened to this episode, is there anything that you have learned?

SPEAKER_00 54:35

Because we have been been fairly diverse.

SPEAKER_01 54:38

Yeah. But more importantly, I would like to know people's personal stories with BMI because a lot of people will listen to this and go, I fucking hate BMI because when I was six years old, a doctor told me that I was BMI 30 and I needed to go on a diet, and I that stuck with me ever since. I've had all of these stories from clients, and I think if people chimed in with their experiences with BMI, it would probably be a better learning curve for everyone else who had a different perspective. Because when you see people in the comments all giving their own anecdotes, I think it helps shine a light on social issues that people might not be aware of.

SPEAKER_00 55:16

Yeah. That is a good suggestion.

SPEAKER_01 55:18

Oh, cheers, babe. Thanks a lot.

SPEAKER_00 55:20

Looking forward to hearing from some of you.

SPEAKER_01 55:22

Hope you've enjoyed the episode. We'll catch you next time. Hi five, later potato.