The skinny on the Body Mass Index (BMI)

2009 February 8
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By M Parrott
Article ID: 137

Round up a group of ten-year-old children. Put each one on a scale. One third of those children are overweight. Expand your view, and you’ll see that 23% of school children are overweight. So says the British government. They also state that within four years, one out of three adults will be overweight. I’m not sure if this scare trend is common across all cultures, but let me tell you now it is bull. The problem here is that to make these weighty judgements, the government uses the Body Mass Index (also known as the BMI) which is so innately flawed that you might as well flip a coin on whether someone is obese or not.

What is the BMI (Body Mass Index)?

Let’s start with the BMI’s origin. A Belgian mathematician and sociologist named Adolphe Quetelet created the Body Mass Index between 1830 and 1850. He did this as a way to compare a person’s height with their weight. This technique was originally meant to aid in social science education, and wasn’t intended to determine obesity levels. BMI was not meant for medical diagnosis. So how can we use it to see if people are obese? If we’re analyzing a specific individual, we can’t! At least, not reliably.

Let’s consider the problem with using weight as an obesity measurement. You might be thinking, “well, of course your weight determines if you’re obese.” Not really. Muscle and bone density play a big part. Compare equal amounts of muscle and fat, and you’ll find the muscle weighs a lot more, at least four times more than fat. So a BMI label for someone with no fat but a lot of muscle will be obese. For example, Michael Jordan is obese according to the BMI and I guarantee he is a lot more fit than anyone reading this. I’m normal weight and Jordan is certainly in better shape than I. So here it is; if athletes are classed as obese then how can we possibly apply this formula to anyone? How can the BMI tell us if we are obese or not? (Yes, we can take additional factors into account like diet and exercise, but the BMI doesn’t do that.)

One of the key measurements of the Body Mass Index is weight. But weight isn’t even an accurate measurement of how healthy you are. Some health fanatics and personal trainers will tell you that there are no genetic factors behind being fat, but this is far from true. Consider the variation in ethnicities. Look at Viking descendents and Greek descendents and you’ll see a vast difference in structure. Those of Viking descendents are often higher than average weight; they have a larger bone structure. Greek descendents have a thinner bone structure and are in comparison generally lighter. So back to the BMI: why is one formula applied to everyone of every ethnicity if different ethnicities are genetically pre-disposed to be different weights?

If you’d like to see how morbidly obese you are – or are not – see this BMI calculator from the Center for Disease Control.

Diet and exercise are good for you. If you eat right you will be your natural, healthy weight. Yes, the BMI may label you as obese or over-weight. But so what? That’s the weight at which your body is healthiest.

Another detrimental part of the BMI is the social aspect. No matter what you look like, no matter how thin, fat, muscular, dimple-ridden, smooth skinned, pot holed or deformed: you’re still a good-looking piece of humanity. It doesn’t matter if you are the image of a greater being or the creation of self-directed chance. Humanity is a beautiful race. Live life however you want to live it. Don’t be bullied by anyone, especially the government or media, on how you should look. It’s your life; it’s your choice.


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5 Comments
2009 July 4
Alida Ryerson permalink

So the word is spreading along with our waists… NPR this morning had their mathematician reveal the fallacy of the BMI. It was pleasing to be able to say to my friend… Oh I knew that already…..

Thanks for your efforts. I look forward to the broadcasts.

2009 July 23
Barbara McNichol permalink

Thanks for your references. I did a little research on the BMI for my daughter who is almost 8. She is very active and not the least bit plump in appearance but she is tall for her age. The “ideal” BMI for kids is calculated by age so her BMI (21) puts her in the obese category. I did some more calculations. At the same height and weight she would be overweight at 10 and healthy at 12. To get her to a healthy BMI she would have to lose 10 lbs. Believe me she does not have 10 lbs to spare. I have 10 lbs to spare, though I have a “healthy” BMI so I know what 10 lbs to spare looks like.

2009 October 25
Ken McFarlane permalink

When an item makes a statement that is clearly wrong, it calls into question every statement in the article. It is ridiculous to say “muscle weighs … at least four times more than fat.”
Muscle density is about 15% more than that of fat tissue, not 300% as ‘four times’ suggests. A pint of muscle would weigh about 18 ounces, and a pound of body fat about 15 ounces.

As for football players being ‘healthy,’ NFL player average life expectancy is less than 60, compared with nearly 80 for the general population. So much for ‘healthy.’

BMI is used because it is easy and non-intrusive to measure and that’s important for large studies.  Other measures, like waist-to-hip ratio or body fat fraction are sometimes proposed as a standard, but also have issues. Some would not agree to undress completely and  be immersed in water up to the neck to participate in a study.

2009 October 25
Ken McFarlane permalink

A correction: “A *pint* of body fat weighs about 15 ounces.” A pound is only 15 ounces in today’s packaging. Canned goods (tomatoes, beans) used to come in 1-pound cans.

2009 October 30
M Parrott permalink

Ken, my dear, I am British, so a “Football player” is a “soccer player” to you.
 
As for the muscles versus fat bit you are absolutely correct; I was wrong about how much more it weighed. Muscles weighs around 18% more and I shall be in contact with Andy shortly to get modified. However I disagree that it puts the whole thing into question. My other points still stand and surely my willingness to modify the post after something I have said is shown to be wrong gives some credibility?
 
It doesn’t matter if the BMI is non-intrusive, it’s still being used and abused to make people feel bad about themselves. People wonder why so many kids have anorexia and bulimia nervossa blaming it on tv and adverts when the government is pounding into our heads that we are all overweight and they are doing this with a ridiculous measurement. It is not created to be used as a way to say if you are over-weight and therefore should not be used so.
 
Humanity is a beautiful thing skinny or not. You are either the creation of a higher being or evolution depending on your beliefs. Either way that’s fantastically amazing. Your skin cells alone are something to be astonished at. Don’t feel bad because society tells you you’re fat.

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