Chances are at some point you have pulled up a BMI (body mass index) calculator and punched in your height and weight. I did it just now myself, 5 ft. 8 in. and 175 pounds… BOOM, overweight! Almost obese actually.
I am scared to punch in my true height (which might be 5 ft. 7 in.) so I am sticking with what the height I tell people I am at 5 ft. 8 in.
Here’s the thing about BMI, it doesn’t take anything other than height and weight into account. Age, sex, race, body frame, muscle mass, and other factors are left out.
Now to be fair, I would probably benefit from losing a few pounds. I am not necessarily using myself as an example of how it’s wrong, rather of how the BMI calculator was so quick to give me a ‘definite’ answer that it cannot possibly account for everything about me and what makes me healthy or not healthy. So, let’s take a dive into this and see, what’s really going on with BMI?
The History of BMI
The first question I asked myself is where did it come from? Why is it even a thing? It isn’t a secret that most health and fitness professionals know that BMI calculations aren’t particularly useful when helping someone get healthier. In fact, I think every single professional that I have talked to or listened to knows this.
But BMI calculators are still very common and widely used by lots of people every day.
I did some digging and found that the origins of BMI can be traced back to a Belgian man named Adolphe Quetelet from the early 1800s. There was a lot of emerging theories about using metrics and data for more applications and he sought to find a way to use data for ‘finding the average man’ and to write about it in his book: “A Treatise on Man and the Development of His Faculties”.
Quetelet collected as much data as he could and created a formula he called the Quetelet Formula that took the height and weight of Belgian men of the time and measured their thinness or thickness.
In the 1940s a life insurance company took hold of this process and used it to figure out how much to charge for policies because it was thought that the height and weight of a person was a big indicator of their mortality risk. Later in the 1970s it had been coined the body mass index that we now know of and started being used by doctors and health offices regularly.
That’s the history of it, we have been using it that way ever since. The biggest problem we find when looking at the history of it is that in neither of these scenarios that drove the start of a BMI metric was diversity represented.
What I mean is that it was first developed by an early statistician for his sociology book using only Belgian men of a certain age that were available for study in the 1830s and was never intended to measure obesity. Then popularized in the US by an insurance company that only evaluated white males of a certain age who were looking to purchase life insurance policies.
What is BMI and how is it calculated?
The body mass index is a chart that uses an individual’s height and weight to label them underweight, normal, overweight, and obese. The calculation is: your weight in kilograms divided by the square of your height in meters. In US measurements you would do it this way: your pounds divided by your height in inches squared then multiplied by 703 to convert to metric and find your place on the chart.
Using the actual formula isn’t really necessary if you have access to the internet because there are countless BMI calculators online.
This calculates (not very accurately) your body’s fatness, or in other words your thickness or thinness. As you can imagine, this formula cannot calculate your body fat directly, it is only a moderate correlation between your weight and height that can be used for screening purposes.
What does BMI not account for?
While it is true that there is often a connection between height and weight on your status as overweight or underweight, any two people with the same BMI likely have big differences about them. Think about factors such as these instances that are largely true of bodies at the same number on a BMI chart:
· Women tend to have a higher body fat percentage than men.
· Older people tend to have more body fat than younger people.
· Athletes tend to have less body fat than non-athletes.
· Race and ethnicity groups tend to have different body fat percentages.
· Body frame, bone density, and muscle density affect weight.
Additionally, BMI numbers can be very skewed at the ends of the height range. Meaning that thickness is exaggerated in tall people and thinness is exaggerated in short people.
As an example, studies have been done of athletes, boxers in particular, and shown that their BMI fluctuates when they are in and out of training as their muscle density increases and decreases, even though a particular boxer is remaining healthy throughout – it is simply that their body and weight fluctuates as bone density and muscle density change with their training.
In another illustration, data has also been recorded of people in different stages of life, through young adults years, middle aged years, and into older age, a person who is active and healthy throughout life may still experience different body makeups in their bones and fat percentages simply associated with their age and not an indicator of their health changing.
Often times the eye test is a better evaluation of how overweight or underweight someone may be. When examining someone, a trainer or doctor will be able to see if an overweight or underweight label from the BMI chart is worth taking seriously.
Think about two different people in a crowd and assume they are the same weight and height, but one of them has very broad shoulders, thick legs and arms and a big head, while the second subject has a large stomach and neck. This picture could help you see that two people putting the same height and weight numbers into a BMI calculator could come up with the same label but represent very different body situations.
Where can BMI be helpful?
BMI charts can be helpful for doctors and healthcare professionals as a screening tool. When a doctor office is taking lots of data on charts and gathering as much helpful info before the doctor sees a patient, BMI can be helpful in indicating to the healthcare professional what health risks may be present that they should be prepared to address.
Once seen be a doctor however, a good doctor will be able to assess if the initial BMI calculation is accurately depicting the situation and can gather more specific data then provide more personal care or instructions from there.
When should I stay away from BMI?
When trying to understand your own situation of being overweight or underweight, BMI should not be taken as a conclusive answer.
Too many regular people, like you and I, look at BMI chart and decide right there if they should be worried or not. In reality, that is a poor way to assign how you feel about your body. As mentioned before, give yourself a look in the mirror and consider how you look. And more importantly, there isn’t a box on the BMI calculator that lets you say how you FEEL. If you notice you are low on energy, having back pain, or struggle with what you think should be regular tasks – that is a better indicator that it’s time for you to take some action.
BMI does not measure your health. It’s that simple. BMI is a tool that can be used by trained professionals to prepare for potential health risks.
The biggest downfall of BMI numbers is that it doesn’t calculate body fat percentage, skinfold thickness, diet, exercise and demographics – all things that need to be taken into consideration when evaluating health.
A 6-foot-tall athlete that weighs 200 pounds and an office worker living a non-active lifestyle of the same height and weight may both be calculated as overweight according to the BMI chart – but that wouldn’t be true in both cases.
In my research I came across multiple authorities that state BMI is a good evaluator, such as the CDC saying, “BMI is a reliable indictor of body fat” or the National Library of Medicine saying BMI is a “good way to decide if your weight is healthy for your height”.
Both institutions do still explain what BMI is actually calculating and used for, but maybe they should consider rewording these statements to better educate people and not encourage them to make decisions based on the BMI label alone, but rather to understand the place BMI labels should have in our health evaluation alongside many other factors involved.