, Q&A Wednesday, Tools For Weight LossQ&A Wednesday: Why Does Body Mass Index (BMI) Matter?

Q&A Wednesday: Why Does Body Mass Index (BMI) Matter?

Tricky, tricky, tricky…

Q: I keep seeing this BMI thing everywhere, and I know that my girls aren’t overweight, but their doctors tell them they are and they need to lose weight. If they don’t look overweight, why does it matter if the BMI says they are?

If the question is whether or not the body mass index (or BMI) matters… the simple answer is that in reality, it doesn’t.

No, really.

But before you go writing off your physician’s advice, let me explain it a little clearer.

The BMI is merely a calculation based on your height in correlation to your weight. It is a ratio of what one’s frame is carrying in weight, and used as an estimation of one’s health. Not necessarily their health today, but their health tomorrow.

The idea is that there is a likely height-to-weight ratio that estimates just how much weight a particular frame can manage. Anything beneath that weight can imply that your organs aren’t being supported, you might be suffering an illness or you might be malnourished. Anything above that weight can imply that you have too much fat crowding your organs, you might be suffering an illness or you are “over-nourished,” so to speak.

Look at that paragraph – see all the uncertainty? “Likely,” “can imply,” “might,” “might”… c’mon.

The BMI was invented sometime between 1830 and 1850... before slaves were freed. Think about that.

The BMI wasn’t paid much attention until approximately the 1970s (over 100 years later… think about that, too) when a guy named Ancel (An-sill) Keys created a study titled “Indices of Relative Weight and Obesity” which used the BMI, gave it its “body mass index” name and popularized the simple ratio. Calling it an adequate measure of body fat percentage in the human body, and because it was a cheaper and quicker measure than what most researchers were using at the time, the BMI spread like wildfire. Flaws and all.

I already have a problem with Ancel Keys because he’s the reason why we swear that fat is the reason we’re fat, even though we’ve now suffered through two decades of “fat free/low fat” products and are fatter than we’ve ever been. The details of his Indices study are basically that he studied approximately 7,400 men in five countries. Women? Meh, y’all and your little bodily differences weren’t needed for such a study.

In the 1980s, when the National Institute of Health began advocating the BMI for regular use in treating patients, there were differing values for men and women.. and the marking number for being “overweight” rested somewhere around 27. Once the late ’90s hit, both men and women were now to share the same standard scale, and the marker for being “overweight” was moved down to 25.

Why, you ask? If you ask this guy, he’ll tell you the NIH and the CDC were in cahoots with one another so that they could create an obesity epidemic… thus resulting in more money being given to both entities. I’m a conspiracy theorist and all, but wowzers. The change in the threshold for obesity did result in something like 30million more Americans being classified as overweight.

If there are all these problems with it, why is it still in use? Because, quite frankly, while it’s often wrong… it’s also sometimes right. Though that “overweight” label might hurt some people’s feelings (why, I don’t know), its labels like “underweight” and “obese” that signify much more than the “overweight” category. (Although, I must admit, I doubt you need a scientific calculation to identify an individual as obese. Seems like a waste of time.)

Personally, I think it’s stupid. The body responds to its environment. Some athletes are extremely active, and the body will recognize that it may need to burn calories and lose weight to help accommodate that activity. Those athletes are, by definition, underweight. Some individuals have labor intensive jobs that require lots of heavy lifting, and the body will respond by packing on the muscle. Those individuals, by definition, are overweight. My bodybuilding friends? They’re shooting the BMI the finger because they’re obese.

If the body mass index is merely meant to measure the amount of mass a body should/could carry… and we know there’s a major difference between a body carrying fat and a body carrying muscle, for our doctors to use a measurement that doesn’t quantify muscle in comparison to fat is a medical fail. Seriously. Neither Keys nor the originator of the BMI intended for it to provide such blanket assumptions in such a specific fashion. “You must be like these other people because you share the same height and weight.” That’s what the BMI says. That’s why it’s so stupid.

I, personally, find the body fat percentage to be far more valuable in gauging my physical wellness. The body fat percentage estimates what percentage of your body appears to be purely fat. The “average American female’s” body fat percentage is somewhere around 32%, while the typical athlete is around 22%.

The bf% is a much more valuable number because it acknowledges that those in the overweight category may simply be muscular, and those on the thinner side may still be hiding some fat that needs to be addressed. There is no cheating or hiding behind “unfairness” with the body fat percentage. A caliper or a hydrostatic test is usually used to measure bf% – I use an electrical machine at my gym – but there’s also this quick and dirty calculator that I use to keep track, and it only requires a tape measure. You’ll get two numbers – take an average between the two numbers, and you’ll have a better and much more valuable estimate. If body fat is the issue (not muscle), then getting numbers that address specifically that definitely helps.

Lastly, if your body mass index still has you down… head on over here and see others who, apparently, are in your “weight group” and feel a little bit better about yourself. Lots of beautiful people over there, wondering how or why this arbitrary ratio matters so much. Just like the rest of us. (This one is my personal favorite.)

PS: Show a little love by voting for me in the Black Weblog Awards for Best Health or Wellness Blog category! That’s right – BGG2WL is a finalist thanks to you! Let’s do what we can to bring it home!

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About the Author:

The proud leader of the #bgg2wlarmy, Erika Nicole Kendall writes food and fitness, body image and beauty, and more here at #bgg2wl. After losing over 150lbs, Kendall became a personal trainer certified in fitness nutrition, women's fitness, and weight loss by the National Academy of Sports Medicine. She is also certified in sports nutrition by Precision Nutrition. She now lives in New York with her husband and children, and is working on her 6th and 7th certifications because she likes having alphabet soup at the end of her name.


  1. thelafemmenoir August 18, 2010 at 11:23 AM - Reply

    I always knew the that BMI index was a sham because if you look at history, times were hard and food was not as abundant then as it is now. People were actually starving or living on very little at the time. Plus, the scientist never intended for his material to be used in this manner anyhow.

  2. BAnjeeB August 18, 2010 at 12:22 PM - Reply

    Very good piece. I bought one of those hateful scales that tells me my body fat percentage a few years back. While I think all scales are inherently evil, it has been a good way to keep me on track. It’s not the only way I keep track of progress, but it is helpful sometimes to see it on that little screen.

  3. aisha August 18, 2010 at 3:22 PM - Reply

    I think BMI is one of many measures. It’s a good starting point. Anecdotally I hear people who are unhappy with their wieght, always on diets, in plus sized clothing and never work out eschewing the BMI. They haven’t even tried to even come to the top of range. That’s the problem, using the BMI caluclation flaws as an excuse to best you can be.

    • Erika August 18, 2010 at 3:44 PM - Reply

      It’s an imperfect measure because it doesn’t take into consideration the quality of the mass that the frame carries.

      That’s part of the reason why I hate addressing the idea that “minorities and women aren’t properly measured under the BMI… they get a fair disadvantage” because it’s disingenuous. Those who are in the overweight category might be given an “OK” but those in the additional levels beyond such… still have a reason to be concerned. The idea would eventually get passed through a big game of telephone, and result in people giving passes for morbid obesity because “the BMI isn’t right.”

      This is why the body fat percentage makes much more sense to me, honestly. Thanks for commenting! 🙂

  4. Streetz August 19, 2010 at 1:59 PM - Reply

    THank you for the BMI clarification. Too many people (including my former physician) go by this as gospel. Measiring weight vs lean body mass vs body fat vs measurements are waaaaay more accurate.

  5. huny August 19, 2010 at 6:51 PM - Reply

    erika, fantastic post as usual. when I first saw the title I cringed because it gave the impression you were going to champion the BMI. which I knew didn’t sound like you at all lol.

    “Anecdotally I hear people who are unhappy with their wieght, always on diets, in plus sized clothing and never work out eschewing the BMI”

    hmm. interesting wording you used here, aisha. people in “plus sized clothing” don’t have a monopoly on being unhappy with their weight, always on diets or not working out. plenty of thin people do all of those things at well but nobody seems to care cause hey, they “look” healthy, right?

    not all plus sized people (defined as a size 12 US and up) are unhealthy nor make excuses for their larger frames, either. I’m getting tired of this assumption. I’m also not feeling the implication that if you’re plus sized you aren’t “the best [you] can be”.

  6. Merewen October 19, 2010 at 10:19 PM - Reply

    I’ve always had a problem with BMI. It doesn’t take into account bone structure or muscle mass. In High School I was very very very active in sports and cheerleading. 150lbs lots of muscles and very LARGE breasts. When I tried to join the Marines after school the recruiting officer pulled out that chart and I was floored. He told me I needed to weight 135lbs. For me personally….eewwwwww. I would have looked like a crack head! If I am able to keep up and/or excel then what’s the problem?

  7. Nora December 7, 2010 at 1:50 PM - Reply

    Recently there was a study saying what many of us already knew – BMI is *NOT* accurate for people of colour! Because they *gasp* only considered white bodies when creating this system! How…unsurprising.



  8. Lyn December 20, 2010 at 12:30 PM - Reply

    I found the BMI to be frustrating as well. Though I have weight to lose, before I gained it I was very athletic. My family is a very athletic muscular bunch. But when I go to the doctor I get called OBEASE all the time, which does irritate me because in my mind that word seems to embody someone who can’t touch their toes, run, walk up a flight of stairs without losing their breath, or fit in a bathtub comfortably. I am none of those things. Im glad to read the facts about the BMI so now I wont let it weird me out as much.

  9. Melissa February 16, 2011 at 8:09 PM - Reply

    I have used the BMI from time to time as an overall gauge of where I am. I do figure competitions and I rely on a combination of tools to decide how my physique is progressing toward competition day. I believe, that for me, body measurements combined with a body fat calculator work the best. I do use the scale, however, because I have a pretty good idea what my physique should look like at different weights.

  10. HerMindandBody November 13, 2011 at 1:48 PM - Reply

    Although BMI is probably not accurate for atheletes, those with physically demanding jobs, or elderly, I think it is a good staring point and a simple way to assess your current state. I think BMI is used more as a convenience. I do have a scale that measures body fat, but for those who do not have access to a body fat analyzer, it’s a start.

    • Erika Nicole Kendall November 13, 2011 at 2:57 PM - Reply

      …yeah, unless you’re lifting weights, as well.

      • irene May 21, 2012 at 2:54 PM - Reply

        So I checked out the calculator for body fat percentage and I am completely mortified. My percentage was 78.35:( I knew I had a weight problem but seeing the numbers ummm I just don’t know. Where do I began with my journey for weight loss??

        • Erika Nicole Kendall May 21, 2012 at 8:24 PM - Reply
          • irene May 23, 2012 at 9:34 AM - Reply

            It’s been two days and I have been pouring over the site. The info is amazing and absolutely on point. I have cleaned out my fridge and though it’s not much I walked for 15min. I do have a question I am scared in a way to lose weight and have so much extra skin when I reach my goal. Any tips on what I can do to tighten up while losing weight?

            • Erika Nicole Kendall May 23, 2012 at 2:35 PM - Reply

              Yes. Eat your vegetables. Eat LOTS of them. Eat ALL the veggies you can get your hands on. LOL But I’m serious. LOL

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