I have a problem with Body Mass Index (BMI) as a measurement of health.
Almost everyone has heard the acronym; BMI. And while many have an idea what it is, let me start my arguments – and yes, they are arguments – with the definition of the term.
‘BMI is a person’s weight in kilograms (kg) divided by his or her height in meters squared.’
This is one way to define it. Simple, huh? But don’t be fooled. This seemingly simple definition is anything but. However, this isn’t the time to jump the gun. So let me layer on the science of it.
BMI can also be calculated using other variables like pounds (instead of kilogram) and with some calculators, it can be computed using feet and inches instead of meters. The main components are weight and height. For the purposes of this article, I will use kilogram to meters (or feet and inches) for my measurements.
Let us get into it, shall we?
For a little over a hundred years, BMI has been used as the standard of body measurement since Adolphe Quetelet, the Belgian Mathematician, Astronomer and Statistician, developed the unit of measurement. It seeks to measure whether a person is underweight, normal, overweight or obese. Right now, the formula for calculating BMI is;
BMI = weight (kg) / height (m2)
And generally, it is accepted that:
- A BMI of 18.49 or below means a person is underweight;
- A BMI of 18.5 to 24.99 means they are of normal weight;
- A BMI of 25 to 29.99 means they are overweight;
- A BMI of 30 or more means they are obese.
Until sometime last year, I accepted this measurement as truth. I studied Biochemistry and I remember thoroughly enjoying the nutrition classes because we dealt with things like BMI. I was especially happy about it after I learned how to help malnourished babies get back to ‘normal’ weight. Those were the aspects of Biochemistry that made me love the course.
But recently, I had a run in with a loud-mouthed doctor when I went to the hospital with my mum. She had suffered a heart attack. The doctor stabilized her and after she had taken the drugs he gave her, she stood up and went into the restroom. As soon as my mum was out of earshot and we were alone, the doctor said something to the tune of, ‘if you don’t want to suffer what your mother is suffering, you need to lose weight quickly. Can’t you see that you are too fat?!’ (And yes…that was almost verbatim). At first, I feigned laughter because he was a much older man and I was worried about my mum. And then I wondered why he was making the comparison because my mum is way slimmer than I am.
‘Climb the scale there. I am sure your BMI will confirm what I am telling you. You are too overweight!’This time, I didn’t laugh. And because I am not one to suffer a fool gladly, I made sure I spoke pointedly at him so that he would get the message. ‘I am not your patient. Your job here is to get my mum better; nothing more. Can you KINDLY focus on that?’
I am sure he hadn’t been spoken to like that in a while. He kept quiet and waited for my mum to return. When he was done with his duties, my mum and I left. It wasn’t until later that I heard he told my mum I was a rude child. It gave me so much pleasure to have put him in his place. But… I digress.
That day, I was so mad at the doctor. I saw what he did for exactly what it was; fat shaming. The man didn’t really care about my health. He didn’t have my medical history nor had he engaged me in a conversation to find out about my lifestyle. All he saw was a fat girl that he thought he could talk to in whatever way he felt he could. I wished I hadn’t been so ‘respectful’ of him and had given him a proper tongue lashing. And the more I thought about it, the angrier I became.
But then, the anger passed. I looked at myself and admitted what I already knew; I am fat. My BMI says I am obese. But the question I asked myself after reacceptingthis fact was…am I healthy?
This question prompted another. ‘If BMI used just weight and height to classify people into normal (which is translated to mean ‘healthy’) and obese (which is translated to mean ‘unhealthy’), could the unit of measurement be more about aesthetics than it was about health?’
I decided to pursue the thought.
With almost 8 billion people in the world ranging from the shortest person – Chandra Bahadur Dangi who is just 54.64 cm – to Robert Wadlow who is said to have been the tallest person in the world (standing at 8 ft 11.1 in), there couldn’t possibly be a ‘normal’ height for people. This also meant that there couldn’t possibly be a ‘normal’ weight for people. As I processed these thoughts, I wondered: if you can’t have a normal height or weight, how can we have a ‘normal’ BMI? Because, what may be normal to a 5’9 man weighing 70kg may be underweight for a 7’1 person of the same weight, and overweight for a 5’4 woman of the same weight. So…if there was no constant in all this, how could the BMI be accepted as the appropriate unit of measuring ‘normal’ health?
To process this thought further, I started doing some basic mathematics in my head. It was too stressful for me, so I found a BMI calculator that used the kilogram to feet and inches ratio. I started to calculate BMIs for a range of people if one variable was kept constant. Here is what I found.
Chart showing varying BMIs where;
I used the RKM BMI Calculator to arrive at my figures. The first thing I noticed as I calculated these BMIs was that I got a prompt only when the calculated index was termed overweight. It was surprising because, if the worry was about determining health, it should have prompted me when all the figures that fell into the underweight categories were calculated. In fact, all the BMIs above 150 showed an ‘impossible’ prompt; meaning people couldn’t – or maybe shouldn’t – have those indices.
This seemed to be buttressing my view; BMI is designed to keep people skinny more than it is to keep them healthy. From my calculations, you can see that the ‘best’ weight seems to be between 50 and 100kg. Anything more than that and we have the obesity label slapped on an individual.
But let us think about this a little more.
Lebron James, the American and Los Angeles Lakers Basketballer, is approximately 6 feet 7 inches tall and weighs 113kg. His BMI is 28.06. His BMI says that he is overweight; and thus, unhealthy. Serena Williams – the world class tennis player – is 5 feet 7 inches and weighs 70kg. Her BMI – 24.17 – shows her to be of ‘normal’ weight but you would never believe that with how much people tear into her for supposedly being ‘big’ and ‘towering’. Remember that nonsense by Maria Sharapova? The sheer idiocy! Moving on, let us look at Simone Biles, the American gymnast. Her 4 feet 7 inches frame weights 47kg. This brings her BMI to the upper limit of ‘normal’. And finally, Shaq O’neil – the former Basketballer – who weighs 147kg and stands at approximately 7 feet 1 inches has a BMI of 31.54. This means that he is obese.
Here is why all these make no sense.
BMI doesn’t take into account a person’s food choices, lifestyle, exercise or even whether their weight is fat or muscle mass. In fact, it doesn’t take gender differences into account, or physiological changes like those seen with pregnancy. It focuses on two variables that are too simplistic to be effective. Which is why, looking at just their heights and weights, it is simple to say Lebron is overweight and Shaq, obese. It is also easy to conclude that based on these descriptions, they are unhealthy. Is that so however? The answer is no.
Lebron is an athlete with a strict exercise and feeding habit. And it is clear even just by looking at him that he is made up of more muscle than he is of fat. Serena may look big but at 70kg, she is pretty average. Simone doesn’t in anyway look like she weights 47kg. And while Shaq is supposedly obese, his frame is fitting for his weight. Therefore, BMI in their cases is a redundant measure of their state of health.
This made me do more research to see if other people considered BMI to be a flawed unit of measurement for people’s health. And the more I searched, the more it seemed that the science community was agreeing with me; or better put, I was agreeingwith the science community.
It was while basking in the fact that I was right that I stumbled onto something surprising. There is a new alternative to BMI! It is called the Relative Fat Mass Index or RFM.
I was intrigued. So I learned more about this new method.
It would seem that to calculate what your RFM is, you would be expected to measure your height and waist circumference, and then use this formula below to calculate it:
64 − (20 × height/waist circumference) + (12 × sex), where sex = 0 for men and 1 for women.
This means that the formula dis-aggregated is thus;
MEN: 64 – (20 x height/waist circumference) = RFM
WOMEN: 76 – (20 x height/waist circumference) = RFM
On a side note, I don’t know why there is a difference in the formulas for men and women. I will have to find out and update.
So what makes RFM a better alternative? I think the fact that RFM presented near similar results to the dual energy X-ray absorptiometry (DXA) body scan – defined as the gold standard for measuring body tissue, bone, muscle and fat – is something to look into. In simpler terms, RFM presented similar results to the ones produced by a machine and, I am not saying machines cannot be wrong, but… it presents a pretty convincing argument.
There are other methods that have been developed to accurately measure a person’s health based on the fat tissues in their body, but BMI still remains the most commonly used method. Why are these other methods – shown to be way better at telling the health of a person than the BMI – not catching on in general practice?
I think the answer goes back to the doctor’s reaction to my weight.
BMI is not designed to give people an overview of their health. If it was, it would put as much emphasis on underweight people as it did overweight and obese people. Again, look at what happened with the calculator I used. It prompted me every time the result was ‘obese’ but never when the result was severely underweight. Both extremes present potential health problems for people, but only one got the stick.
At this point, the answer is pretty clear to me; BMI is designed to keep the populace thin more than it is to keep it healthy.
To give this more credence, it is important to note that for centuries, the global beauty standard for women was skinny or thin; with few exceptions. Women did all they could to maintain weights that were nearly impossible to keep without extreme exercise, starvation or severe health risks. It is why many people initially didn’t call out anorexia, bulimia, excessive smoking and even starvation because it achieved the results that were accepted; skinny women. It is also why when a skinny person eats a lot of food, nothing is said to them. In fact, they are praised for being able to put so much away and ‘maintain their figure’. But God bless that a fat person eats…
However, with the advent of the body positivity movement, things have begun to change. There is a conscious decision to show that health is not just about weight and height, but also about the quality (and quantity) of food eaten, whether a person is active or sedentary, how much exercise they are doing, and what makes up the bulk of their weight; fat or muscle. Like most social changes, it has been met with fierce rebuttal and in some cases, attacks. But it is to be expected.
I believe that overall health is determined by way too many factors to be allowed to rest on the shoulders of archaic methods of measurement like the BMI. And fat doesn’t necessarily mean poor health…just as being skinny doesn’t necessarily equate to good health. So it is time we stopped using BMI to try to shame fat people into losing weight; it is a failing ploy anyways.
I need to clarify that this is not a call for people to disregard their weight as it affects their health. It is important to be healthy and this entails living and eating right, exercising, having more muscle mass than fat tissues and generally caring for your body.
So yes! The time to stop using BMI has come. And if one more person tried to ‘worry about my health’ for me, without taking out time to find out the parameters that determine said health, I am (literally) going to go nuclear on them.
PS: Here are some good BMI Calculators that incorporate other health determinants that you may want to check out.