What is the Body Mass Index and is it the best measure of obesity? - CrowdScience, BBC World Service

Summary

The BBC World Service's CrowdScience explores the Body Mass Index (BMI), a widely used health metric, questioning its relevance and accuracy in today's diverse global population. The discussion begins with individuals calculating their own BMI in their bathrooms, highlighting the simplicity of the measurement. However, the program delves into the limitations of BMI, such as its inability to differentiate between muscle and fat, leading to misclassifications for muscular individuals. Expert opinions from Dr. Naveed Satar and Dr. Francesco Rubino emphasize that while BMI serves as a quick screening tool, it is not a comprehensive health indicator. Alternative methods like the BodPod, which measures body composition, are introduced as more accurate but less accessible. The program also addresses the impact of BMI on health policy and insurance, the role of societal stigma in health care, and the need for a more nuanced approach to assessing health and obesity. The episode concludes with a call for a more inclusive and effective strategy for promoting health, rather than focusing solely on weight as a determinant of health.

Takeaways

• 📊 The Body Mass Index (BMI) is a common measure of body fat based on an individual's height and weight, used to assess if someone is a healthy weight.
• 🌍 The World Health Organization (WHO) categorizes BMI scores: 20-25 is considered normal, 25-30 overweight, 30-35 obese, and over 35 morbidly obese.
• 📈 Global obesity rates have doubled since 1990, with one in eight adults now considered obese according to the latest figures.
• 🏋️‍♂️ The BMI does not account for muscle mass, leading to inaccuracies for individuals with high muscle density, such as athletes.
• 👨‍🚀 BMI was invented in the 19th century by Adolphe Quetelet, a Belgian astronomer, who was interested in the 'average man' or 'ideal man'.
• 🏥 The modern term 'Body Mass Index' was coined by Harvard physiologist Ancel Keys in 1972, who noted its limitations but found it a useful tool for population studies.
• 🧬 BMI is criticized for not being individualized, as it does not consider factors like bone density, ethnicity, or distribution of fat.
• 🏛️ Despite its flaws, BMI is still used as a screening tool in healthcare to identify potential health risks associated with excess weight.
• 🌡️ Alternative measures to BMI, like the BodPod, bioelectric impedance machines, and waist circumference, provide more detailed information about body composition.
• 🌏 There is a call for a more nuanced approach to assessing health, considering that BMI does not reflect the complexity of individual health conditions and should not be used in isolation.

Q & A

What is the Body Mass Index (BMI) and how is it calculated?

The Body Mass Index (BMI) is a common measure of a person's body fat based on their height and weight. It is calculated by dividing a person's weight in kilograms by the square of their height in meters (kg/m²).

What are the BMI categories as defined by the World Health Organization (WHO)?

According to the WHO, a BMI of 20-25 is considered normal, 25-30 is overweight, 30-35 is obese, and over 35 is morbidly obese.

Why was the BMI developed and by whom?

The BMI was developed in the 19th century by Belgian astronomer Adolphe Quetelet, who was interested in the nature of the average or 'ideal' man. It was designed as a population-level tool rather than for individual healthcare.

What are some criticisms of the BMI as a health measurement tool?

Critics argue that the BMI is inaccurate because it does not account for muscle mass, which is heavier than fat. Therefore, very fit athletes or individuals with more muscle can be incorrectly classified as overweight or obese.

What is the role of BMI in healthcare according to Dr. Naveed Satar?

Dr. Naveed Satar, a professor of cardio metabolic medicine, views the BMI as a good screening tool that allows healthcare professionals to quickly assess whether a person may need further investigation or additional blood tests related to excess weight.

How does excess fat affect the body's organs and overall health?

Excess fat can seep into various organs, the blood, liver, pancreas, muscles, around the kidneys, and the heart. It can alter the body's fuel, apply pressure on internal structures, and disrupt the function of filters like the kidneys and liver, leading to impaired function.

What alternative methods are available to measure body composition?

Alternative methods to measure body composition include the BodPod, which uses air displacement, bioelectric impedance machines, and waist circumference measurements. These methods can provide more detailed information about body fat percentage and fat-free mass.

Why might some people, such as athletes or those with more muscle, have a high BMI but still be healthy?

Athletes and individuals with more muscle can have a high BMI because muscle is denser and heavier than fat. Despite a high BMI, these individuals may be very healthy and fit, as muscle mass contributes positively to their overall health and physical performance.

What does Dr. Francesco Rubino suggest about the future use of BMI in clinical practice?

Dr. Francesco Rubino suggests that BMI alone should not be used in clinical practice to determine if someone has an illness or excess fat tissue. Instead, a more nuanced assessment that uses BMI as a screening tool along with other measures should be employed.

How does the BMI contribute to weight stigma and what are the implications for healthcare?

The BMI can contribute to weight stigma by categorizing individuals as overweight or obese, which can lead to shame and avoidance of healthcare. This focus on weight can result in other health issues being overlooked. There is a call for physician anti-bias training to address weight stigma and for healthcare professionals to consider more precise health indicators.

What is the perspective of people from Tonga regarding their BMI and health?

People from Tonga express that their build and body type differ from the standards on which the BMI is based. They argue for a different approach to surveys and health assessments that take into account their genetic and physical differences, rather than relying solely on the BMI.

What is the conclusion of the discussion on the usefulness of BMI as a health measurement tool?

The conclusion is that while the BMI can serve as a quick screening tool for potential health risks related to being overweight, it has significant limitations and should not be the sole measure of health. There is a need for a more comprehensive and nuanced approach that considers other health indicators and respects the diversity of body types and ethnicities.

Outlines

00:00

🧮 Introduction to BMI Calculation and Its Origins

The first paragraph introduces the Body Mass Index (BMI) as a common health measure, explaining how it's calculated and its significance. Marnie and Richard, the hosts, share their own BMI calculations, setting the stage for a deeper exploration of the topic. The segment also introduces the question from a listener named Maik, who questions the usefulness of BMI, particularly for individuals with muscular builds. The history of BMI is briefly touched upon, mentioning its invention by Adolphe Quetelet, a Belgian astronomer, and its adoption by health organizations like the World Health Organization.

05:03

💡 Understanding BMI as a Screening Tool

This paragraph delves into the practical use of BMI as a screening tool with Dr. Naveed Satar, a professor of cardio metabolic medicine. It discusses the limitations of BMI, especially for muscular individuals like athletes, and the need for additional health measures. The conversation highlights that while BMI is a quick way to identify potential health risks related to weight, it is not a comprehensive health assessment tool on its own.

10:06

🏋️‍♂️ Alternative Measures of Body Composition

The third paragraph explores alternative methods to BMI for assessing body composition, such as the BodPod, which uses air displacement to measure body fat percentage and fat-free mass. The discussion with Professor Brendon Noble and Leah Siegel emphasizes that while BMI is useful for population-level analysis, it doesn't account for muscle weight, which can lead to inaccuracies for muscular individuals. The BodPod is presented as a more precise tool for individual assessments.

15:09

🌍 Global Perspectives on BMI and Health

This section examines the global implications of BMI standards, particularly in countries like Tonga where the population's natural build may not align with BMI norms. It includes perspectives from Tongan individuals who feel that the BMI does not accurately reflect their health status. The paragraph also touches on the health challenges faced by countries with higher-than-average BMIs, such as lower life expectancy and higher rates of diabetes.

20:10

🤔 The Role of BMI in Clinical Practice and Stigma

The fifth paragraph discusses the limitations and potential harm of using BMI as a clinical tool. Dr. Francesco Rubino, a bariatric surgeon, criticizes the reliance on BMI for treatment decisions and insurance coverage, arguing that it can lead to unfair treatment and denial of care. The conversation also addresses the issue of weight stigma and its impact on healthcare, suggesting that BMI calculations can contribute to this problem.

25:13

🔍 The Future of BMI and a Call for Nuanced Health Assessments

The final paragraph summarizes the critical views on BMI, suggesting that it should not be the sole determinant of a person's health or treatment options. It includes insights from Kate Manne, a philosopher, who argues for a more nuanced approach to health assessments that doesn't focus solely on weight. The segment concludes with a reflection on the need for better health measures and the importance of considering individual differences in body composition and health.

Keywords

💡Body Mass Index (BMI)

The Body Mass Index (BMI) is a numerical value derived from an individual's weight and height. It is widely used as a screening tool to identify potential health risks related to body weight. In the video, BMI is a central theme as it is used to categorize individuals as normal, overweight, or obese, and is a point of discussion regarding its accuracy and usefulness in assessing health.

💡Obesity

Obesity is a medical condition characterized by an excessive amount of body fat. It is often defined by a BMI of 30 or higher. In the video, obesity is a significant topic as it discusses the rise in obesity rates globally and the limitations of using BMI as a sole measure to determine if someone is obese and, by extension, unhealthy.

💡Adipose Tissue

Adipose tissue is a type of tissue that primarily stores energy in the form of fat. The video explains that excess fat can seep into organs and disrupt their function, which is a health concern. The accumulation of adipose tissue is a key factor in determining a person's BMI and overall health risk.

💡Muscle Mass

Muscle mass refers to the amount of muscle in the human body. The video points out that muscle is denser than fat, which can lead to a higher BMI even if an individual is physically fit. This is illustrated by the example of athletes like Mike Tyson or Serena Williams, who may have high BMIs due to their muscle mass rather than excess body fat.

💡BodPod

The BodPod is a device used to measure body composition, specifically the proportion of body fat and fat-free mass. It is mentioned in the video as an alternative to BMI, providing a more nuanced understanding of an individual's body composition. The BodPod uses air displacement to calculate these measurements, offering a more detailed assessment than BMI alone.

💡Bioelectric Impedance

Bioelectric impedance analysis is a method that uses a small electrical current to measure body fat. The video discusses this technique as another tool for assessing body composition. It is highlighted as an example of how technology can provide more detailed information about health than a simple BMI calculation.

💡Weight Stigma

Weight stigma, also known as fatphobia, refers to the discrimination and prejudice faced by individuals who are overweight or obese. The video addresses this issue, noting that the focus on BMI can contribute to negative perceptions and treatment of individuals with higher body weights, even when they are otherwise healthy.

💡Health Behaviors

Health behaviors in the context of the video refer to actions and practices that individuals engage in to maintain or improve their health, such as regular exercise and a balanced diet. The discussion suggests that focusing on positive health behaviors rather than weight loss may be a more effective approach to health, especially considering the high failure rates of diets.

💡Bariatric Surgery

Bariatric surgery involves surgical procedures that help promote weight loss in morbidly obese patients. Dr. Francesco Rubino, who is mentioned in the video, specializes in this type of surgery. The video implies that for some individuals, particularly those with severe obesity, surgical options may be considered as a treatment, highlighting the complexity of obesity as a health issue.

💡Fat Distribution

Fat distribution refers to where fat is stored in the body, which can have different health implications. The video notes that BMI does not account for how fat is distributed, which is significant because visceral fat (fat around the organs) is more harmful than subcutaneous fat (fat beneath the skin). Understanding fat distribution is crucial for assessing health risks beyond what BMI can provide.

💡Healthcare System

The healthcare system encompasses all organizations and resources that provide medical services to individuals. The video criticizes the healthcare system for its reliance on BMI as a determinant for treatment and coverage, suggesting that this practice can lead to unfair treatment of patients with obesity and a lack of access to necessary healthcare.

Highlights

The Body Mass Index (BMI) is a common measure of body's health, but it has its limitations and is not a precise indicator of individual health.

BMI was invented by Adolphe Quetelet, a 19th Century Belgian astronomer, who was interested in the concept of the 'average man'.

The World Health Organization categorizes BMI as normal (20-25), overweight (25-30), obese (30-35), and morbidly obese (over 35).

Athletes and muscular individuals can have high BMIs, which may not accurately reflect their health status due to the heavier weight of muscle compared to fat.

Dr. Naveed Satar explains that BMI is a good screening tool for quickly assessing if an individual needs further health evaluations.

BMI is criticized for not accounting for the distribution of fat in the body, which can be more indicative of health risks.

The BodPod is an alternative device that measures body composition using air displacement and can provide more detailed information than BMI.

BMI does not consider ethnicity, which can affect factors like bone density and overall body composition.

Residents of Tonga express that BMI does not accurately represent their body type and health, suggesting a need for culturally sensitive health measurements.

Dr. Francesco Rubino discusses the complexity of obesity, indicating that it is not solely a result of lifestyle choices and cannot be entirely controlled.

BMI has been misused as a clinical tool, leading to issues with insurance coverage and access to necessary treatments for some individuals.

Kate Manne, a philosopher, argues that BMI contributes to weight stigma and suggests that a more nuanced approach to health assessments is necessary.

The Lancet commission, led by Dr. Rubino, is considering the future use of BMI and the need for a more comprehensive evaluation of health.

There is a call for physician anti-bias training to address weight stigma and improve patient care.

Dr. Myra Gordon practices weight-inclusive healthcare, focusing on health indicators rather than BMI, to provide more compassionate care.

The relationship between weight and health is often oversimplified, and BMI may not be the most effective measure for assessing overall health.

The future of BMI may involve it being used as an initial screening tool, with a more holistic approach considering other health metrics.

Transcripts

Richard, I'm in my bathroom. Are you in your  bathroom?

I'm in my bathroom Marnie, yeah.  

Okay I need your numbers.

Okay, well, I'm  1m 90 tall or 6ft 2.

Okay and have you got your scales?

I've got my scales here and  it tells me that I am 94 kilos.

Okay so you're 1.9m squared divided by 94 kilos gives you 26.  Congratulations, 26. BMI of 26, okay.

Let's do yours now. Okay, so standing on. That's some kilos. It's 2.62 and then I divide that and it gives  

me 30, which was very brave of me. Well done.

Welcome to CrowdScience from the BBC World Service. I'm Marnie Chesteron. That was me in my bathroom, my producer Richard in his, armed with  

calculators, scales and tape measures because we  were calculating a common measure of our body's  

health: The Body Mass Index or BMI. And the reason? It's because of listener Maik in Germany.

Hi, my name is Maik Muehle and my question for CrowdScience is: What does the BMI tell me about my

health and is it still a useful measurement tool today?

I'm interested in this question because my BMI has always been too high and tells me therefore that I'm overweight, but I don't think that I really am.

I've always been quite muscly and I'm not the tallest. So therefore I think

it gives me a bit of a distorted BMI. So I wonder if we all just come in different shapes and sizes?

My background is that I have worked with dogs for many, many years and we can't be all greyhounds.

So I would describe myself probably more of the shape and size of a labrador crossed with a staffy.

My neighbours are like greyhounds, they can eat what they want and they are really tall and slim.

For me, I have just a different size and shape. So the BMI never gives me an accurate reading, I feel.

The Body Mass Index, or BMI gives you a number. The World Health Organization says that

20-25 is normal, 25-30 is overweight, 30-35 is obese and over 35 is morbidly obese.

Their latest global figures put adult obesity at one person in eight. Double what it was in 1990, they say.

Maik, producer Richard and I have BMIs of between 26 and 30. Maik has a strong feeling that his is

not a fair reflection of his general health. Is he right and if so, why on earth did the BMI rise to

its current status as universal health marker?

Time for a bit of history. The inventor of the BMI was a 19th Century Belgian astronomer called Adolphe Quetelet, who was interested in the nature of

the average man, or some say, “ideal” man.

Even then, he was thinking in terms of populations, rather than individual healthcare. Enter the US health insurance companies who noticed that those at the

extremes of the BMI - the very fat and very thin - had a higher risk of dying. The modern term, Body Mass

Index, was coined in 1972 by Harvard physiologist Ancel Keys, who said the BMI “proves to be,

if not fully satisfactory, at least as good as any other relative weight index as an indicator of obesity”.

Note the qualifier “not fully satisfactory”. But from the 80s onward, the BMI has been used by the World

Health Organization for recording obesity statistics. But what does it tell us?

That's a question for Dr Naveed Satar, professor of cardio metabolic medicine at the University of Glasgow

and Chair of the UK’s Obesity Mission.

It's a very good screening tool. It allows us to work out in a really quick fashion, whether we need to delve into aspects related to excess weight

and also whether I need to do additional blood tests to tell me is the weight that the individual is living

with leading to some complications of her tissues or organs that then needs me to look for, you know,

diagnosing further conditions linked to excess weight.

Why is having a lot of fat bad for you? So if you have excess fat beyond the body's needs, it will seep into various organs, into

the blood, into the liver, pancreas, muscles, around the kidneys, in and around the heart.

And excess fat effectively alters the fuel that the body sees. It applies pressure on the pumps and pipes within

your body. It also disrupts some of the filters of your body, i.e. your kidneys and your liver,

so that their function actually is impaired.

But one of the many criticisms of the Body Mass Index is that it’s inaccurate. Some incredibly fit athletes, like boxer Mike Tyson or tennis legend Serena

Williams, or even people like our listener Maik, have high BMIs, which suggest

they’re overweight and unhealthy when actually they just have a lot of muscle, which is much heavier than fat. Given this flaw, does Naveed see a point to measuring the BMI?

Yes there is. I mean I think again it will allow us as many nations

to look at the track of excess adiposity over time, that's what we've measured. Many people are able to

to measure change you know if they make  a change the best, most accurate way to measure  

that change, at least in the short term, is the  weight, which is measured on scales, which is  

the key part of BMI and as I said it's part of a  screening tool but you're completely correct -

BMI on its own is not enough. We are gradually  understanding that where you put your fat and what  

the consequences of fat are in terms of your body  and how doctors capture that and how we explain  

that to our patients as well as think about other  aspects, what conditions they have and what their  

activities of daily living are, putting all of  that into a package will better help us assess  

whether that individual's weight is leading to  problems that we can help them with.

Naveed says that excess fat puts our bodies under stress, like an overloaded car. And he admits that he still finds

the BMI useful, sort of as a starter test to see whether more measures of a person's health are needed.

But if the BMI is telling fit, muscly types they’re overweight, I wonder what other tools are on offer.

Sometimes here on CrowdScience, we turn human guinea pig and so with a certain amount of

reluctance, I went to the University of Westminster in central London to have a go on something called

a BodPod, an expensive body composition measuring device. There to talk me through the process

were Head of Life Sciences Professor Brendon Noble and nutritional expert technician Leah Siegel.

Today we're going to be doing a BodPod measurement. So it is a measure of your body composition using

air displacement. And the first few things that we'll do, we'll take your height and weight and

you'll put on a very tight outfit, just so that there's no added volume with your clothes.

And we'll also put a lovely little swim cap on for you. And then you'll go into the pod and you'll have your body composition measured.

Great. What's the point of this?

So looking at body composition, people do it for a lot of different reasons. Maybe from a health perspective, maybe from a

performance perspective if they take part in sport or athletics.

So Brendan, is this better than doing a BMI?

Yes. This is almost certainly going to be better than doing a BMI. BMI is very useful, across the population. But BMI is based on height and weight and muscle is very

much heavier than fat. And so if you've got a lot of muscle, this is going to skew things.

I should tell the radio audience, because this is radio, I do not have a great deal of muscle. I wouldn't

say I'm stacked. So more, curvy. Yes. Well, we'll see what the Bod Pod says.

So if anyone's seen any sci fi film where people are kind of frozen for long distance

space travel and they put them in these kind of pods where the little sort of viewing window

out at the front, it's basically that's what it looks like.

We'll open up the BodPod and you can sit inside.

The first measure, it will be very quick. About a minute. You just need to sit still, breathe normally and not talk.

I was sitting in this pod, in my underwear, with my hair bundled under a swimming

cap, trying very hard not to move - wouldn't want my results to be inaccurate.

So we can open the BodPod now. That was weird. So you can exit the Pod if you would like.

As I got dressed, the BodPod algorithm did its calculations. I had to tell it my ethnicity, because if I were a

black Caribbean woman for example, my bones would be stronger and heavier, yet another subtle difference that the BMI doesn’t factor in.

Yeah. So this is a printout of your test results. It has a

few different bits of information here. One of them is the body fat percentage that you can see there.

You also have your FFM percentage. So FFM is your fat free mass, that is everything

in your body that is not fat, so that's your muscle, your bones, your organs.

Is it really worth me having all this information unless I want to compete in the Olympics this summer and frankly I've  

left training a little late for that. After all, the information from the BodPod - how much of me is

fat tissue - is not massively different to what I’ve learned from my BMI. I could also

have used a tape measure around my waist, or pinched an inch of belly fat with some calipers. At the office, I’ve also used

a bioelectric impedance machine. You grip it with both hands and it sends a small and safe

electrical current through your body, measuring resistance. The higher the resistance, the higher

the body fat. They all give me the information that I knew all along - I’m overweight. Borderline obese.

But that’s just me. BMI is a globally used measure and as I just mentioned, BodPod takes ethnicity

into account in a way that weight divided by your height squared just doesn’t. Is that a problem?

Well let’s ask some people from one of the world’s most obese countries according to BMI statistics:

Tonga, in the South Pacific. What do Tongans think about their weight and about the BMI?

For me as Pacific Islanders, mostly I speak for Tongans, we were built different, heavy bones

you know? Big build. Even us here we still see our grandpa, grandma still making it to 80s, 90s

years old. And listening to these surveys on the news, I don't know how it goes but I think for us

here in Tonga, even on the Pacific we need to have our different way of surveys, you know,

for us to really calculate if we are obese or not. Not just judge us by how we look and how

big we are and how big is our legs. We love these legs. You can't stand in front of me if I

run straight to you. You will regret it. That's how we love it, you know, and we still

light, we can run really fast. So don't measure us by how we look.

I've been involved in a few weight loss programmes and whenever we go to weigh in, they give us the recommended BMI for

one's height. And I'm kind of like one of those taller Tongan women 1.75 metres. When they tell me my

recommended weight for my height, I look at that and I think to myself, I'm never going to get there.

I'm going to starve before I actually achieve that weight. And, you know, because one is just

naturally taller or has a bigger physique. So there needs to be some thought given to

constructing a BMI that's probably based on the genetics of those people, rather than prescribing

something where you know one feels like a failure from the start.

That was Fononga Pulu and Sela Latailakepa from Tonga speaking to us there about their BMIs. What they’ve highlighted makes

me think back to listener Maik’s dog analogy. Maybe BMI is not picking up on the difference between a

slender greyhound type or a solid pitbull type. And yet, when I look at the health stats for Tonga

obesity does seem to be an issue - life expectancy in Tonga is below the global average at just over

71 years. And diabetes, which is strongly linked to obesity, is the leading cause of death there.

There are clearly all sorts of factors at play here, from body type, to lifestyle, to availability of healthy food.

But at this point I still want more clarity on how much the BMI measurement is bringing to

the table. What does it teach you about your health?

The BMI doesn't tell you anything about how your organs work, or do not work, which is what normally defines whether a person has an ongoing illness.

And so BMI itself is a measure of risk, but it's not a measure of health.

Meet Dr Francesco Rubino. He’s chair of bariatric and metabolic surgery at King's College London, that means

he specialises in surgery related to obesity. He’s also leading a commission or group at the medical

journal The Lancet, looking at the current obesity epidemic and asking useful questions like “what is a

medically useful definition of obesity” and “should we replace the BMI?”

What does he make of the high BMI scores across many islands of the south Pacific like Tonga?

Yes. I think what is important to say is that we don't actually know exactly what is causing this epidemic and pandemic of

obesity that we have seen in the last many decades. We have assumed that this is a personal decision

to eat more or exercise less. But every scientific piece of evidence tells us a different story.

The reason why there is a pandemic is not completely understood, but it's clear that there are multiple

factors that contribute. So certainly our genetic makeup makes some people more predisposed

to develop obesity even in the same environment. And then there is probably something that changed

in recent years, in the most recent times, like in the last three to four decades, in the

food environment that perhaps is fuelling this pandemic. So reducing obesity to a matter of lifestyle choices is

just inconsistent with scientific evidence.

There is an implication that we trust the BMI because it’s a scientific tool used by doctors. And the suggestion is it’s a tool we can control,

remember, it’s our weight divided by our height squared. We can’t of course control our height,

but we can, the BMI suggests, control our weight.

To some extent it is true that you can modify your weight if you indulge in some type of food and overeating over

a period of time, or if you join a gym and start doing some exercise, you will see your waistline

may actually go up and down as you expect. And so you build this idea that you're in control.

But the problem is that we are only in control for a limited amount of our body weight

regulation. When you start having a level of weight that is significantly elevated and fat mass is no

longer physiologically normally regulated, then thinking that you can reduce and change at wish, undo obesity as you wish, is just naive.

If, as Francesco says, we have limited control

over our weight, is it problematic we're using a blunt tool like BMI to advise patients on how to approach their health?

BMI was never meant to be a clinical tool. And the problem is that we

have used it as such, mostly for insurance purposes, because it's an easy tool to define

who gets coverage for a treatment, who doesn't. But in doing so, we have seen time and again for

many, many years that people can be denied access to treatment based on arbitrary definitions

that take BMI above or below a certain threshold as a reason why

people shouldn't be treated. That absolutely makes no medical sense. But unfortunately, it's the way insurance

coverage in private and public health systems still works.

Yes, I've seen it. I've experienced it. I can tell you that there was a treatment that I was up for and, and I

thought because my BMI is kind of around 30 and, I thought, I know that if this is over 30, this is going to be

something in the arsenal for them to be able to say, no, you can't have this treatment. So when

I knew I was being weighed I just didn’t have any breakfast and peed beforehand.

Well, the paradox is that sometimes a BMI of a certain level is used to say

that people don't if they don't meet a certain threshold, they cannot get coverage for a treatment

for obesity. On the other hand, if you have a BMI that is too high, people don't

let you have access to another treatment not for obesity but for something else, on the assumption

that obesity may actually make it more difficult for that treatment to succeed.

So basically, no matter what people with obesity are always put in a difficult situation.

And I think they're treated unfairly by society at large, but including by the healthcare system and medical professionals.

To me, weight stigma is the single most important problem we have in obesity.

Weight stigma, also known as fatphobia and BMI’s role in it, is the subject of

philosopher Kate Manne’s new book 'Unshrinking: How to fight fatphobia'. I wondered if she’d go as

far as saying the BMI is so crude a tool that we should just drop it completely.

So I think many weight inclusive or weight neutral physicians do believe that for a couple of reasons. One is

that having your BMI calculated at every doctor's visit can be very stigmatising and especially in a

fat phobic society, really leads to demonstrable results of people avoiding health care as they

gain weight. So taking that out of the equation can be quite helpful in helping people not avoid

the doctor, which we have evidence that as women gain weight and as they enter higher BMI classes,

they avoid health care in direct proportion to increases in BMI, which is really serious.

The flip side of that would be that if you do go to your doctor and you do have a high a, say, obese BMI, that

will be the focus of whatever you've gone to the doctor about because the messaging is you need

to lose weight rather than addressing what else you might have gone to the doctor for.

Yeah, totally. And that was the other thing I think is worth mentioning here. Often times the focus of doctors

appointments become, well, you need to lose weight. But the fact is we don't yet have humane, effective,

feasible, safe solutions for people to reliably lose weight in a way that is actually practical

for people and that has good results and does more good than harm, in the majority of cases.

So we know that diets don't work. They have incredibly high failure rates of between 95 and 98%. We know that

actually dieting is a really good predictor of long term weight gain rather than the converse.

And that comes from not just one or two studies, but the most robust meta analyses of really every

long term diet study that's been done to date. So, it may be that the best solution for people is

to engage in health behaviours that are positive, like exercise and eating well and not taking

weight loss as a realistic and feasible health goal for the majority of bodies.

You say there's a moral panic over the so-called obesity epidemic? Is that related to the BMI?

Yes, absolutely. The BMI, many people don't know, the standards for it were changed in about 1998 in the US where

people who were previously categorised as having normal weight became overweight. And similarly,

people who were previously classified as overweight became obese overnight because the standard for a

healthy weight was decreased from about 27 or 28, depending on gender to 25 being the cut-off

for then becoming overweight, for both men and women.

You can't just change the classifications, can you? Well they did, they can and it was based  on World Health Organization recommendations.  

But this wasn't based again on the idea that people are actually becoming unhealthy at

a certain weight. It was based partly on a purely arbitrary idea that the number 25 was a nice easy number for people to remember.

So take the BMI out of the equation? Or I don't know, it

sounds like if you were in charge maybe there's  a lot of awareness training you do?

We desperately need to do physician anti-bias training that includes weight stigma, both because we know  

that physicians are not just guilty of implicit  bias in this regard doctors openly say things  

like they regard fat patients as a waste of  their time and that fat patients are more  

likely to annoy them. They're less likely to want  to help fat patients and they spend less time with us.

But when I speak to really brilliant weight  inclusive physicians like Dr Myra Gordon in the US,

what she has done is take weight out of the conversation. She doesn't assess patients’ BMI.

She goes directly to more precise indications of health, like blood pressure, like blood work and particular

metrics depending on a patient's particular symptoms.

And that both makes patients more likely to want to come back to a doctor who isn't shaming them or making their weight,

which as a fat person, I can assure you that I'm very aware of my weight at any particular time. But

these patients are more likely to want to return to the doctor and get that humane, inclusive care that

could be really life altering, potentially life saving.

So the BMI, invented by an astronomer, which has had its categories - overweight and obese - tinkered with over time, which was never meant

to be used as a clinical tool for individuals and which, as we’ve established, doesn’t take

into account different body types and ethnicities. Is still being used as the way to sort those at

risk of ill-health from those with a so-called healthy BMI. Where do all these problems

leave the BMI in the future - is it a useful quick tool to help doctors assess potential problems related

to being overweight or is it destined for the scrap-heap of medical history?

I think what I can anticipate is that the conclusion of this commission is that BMI alone cannot be used in clinical practice.

That’s Francesco Rubino again, whose commission is looking into, among other things, how the BMI should be used in the future.

We cannot use BMI alone for clinical purposes to understand if

somebody has an illness or if somebody doesn't, or even in the first place if somebody has a really

excess fat tissue or just an excess weight due to other reasons. So what we are advocating is, to

have a more nuanced assessment that uses BMI as a screening tool, but may be looking at other measures as well.

But what do we even want from whatever new form the BMI will take? Is the focus about getting

a better measures of fatness, or is there a better route to measuring health which is less focused on measuring fatness at all?

Kate Manne has some thoughts for those with a BMI of over 30 or 35.

I think that there is a lot of shame and blame when it comes to weight and I think a lot of people feel that

well, there's something a bit wrong with them, that they are heavier because they're somehow not doing

it right. And I really want people to understand that bodies just come in a range of shapes and

sizes. That's always been the case in human history. I think it always will be the case. And I think that

often times the relationship between weight and health is really exaggerated and oversimplified.

I tell my story in the book about having been a person who did have a BMI at one point

in this 'severely obese' category, a BMI of over 40. And I was perfectly healthy.

I had excellent blood work, I had excellent blood pressure, I was very active. And then I lost quite

a lot of weight just through starvation dieting, which was the only way my body would lose weight.

And believe me, I've tried everything and I'm now a lighter, still overweight, but, now a lighter

and much less healthy person because my body has really been through the wringer of starvation diets.

So listener Maik asked us what the BMI could tell him about his health and frankly, given that

his BMI is neither very low or very high, it doesn’t tell us very much. Those who do use it say

it’s a good gateway tool for assessing if someone is at risk of certain diseases. But even the fans of it

admit that it was modelled on the average white man and is only a rough test of whether someone needs further tests.

Those who aren’t fans point out that if you are overweight you face enough stigma from

society without a number on your chart that might mean your doctor focusses on your weight, not

any other medical issue you have. I’m not denying that carrying excess weight increases your risk of

dozen of diseases, from type 2 diabetes to cancer. It’s just I’m left wondering, given that shaming

and dieting haven’t stopped the growing numbers of us who are overweight, what is the best approach

to keeping us healthy. But that’s another CrowdScience for another time. My thanks to Maik

for his question and back to him for the credits.

That's all from this episode of CrowdScience from the BBC World Service. This question  came from Maik in Dresden in Germany and if  

you'd like to ask the team a question then email  it to [email protected] and this programme  

was presented by Marnie Chesterton and produced by Richard Walker. Thanks for listening.