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BMI values are kind of meaningless between 18 and 30

Saturday, July 14, 2012

There is a fun link floating around on the blogs here lately, where you can see how your BMI compares with the averages in other countries and globally overall.


"You're most like someone from Tanzania*
* Compared with other females aged 45-59 in Tanzania"

It kind of underscores the meaninglessness of BMI between the values of 18 and 30. Below 18 can be unhealthily thin. Above 30 is often unhealthily fat. But between those values it's really about body composition. The accompanying article illustrates this pretty well, actually. (Click the "See it in action" tab.)

There are 3 women featured.

- One is Obese Class II (severely obese, BMI 35-40).
- One is underweight (BMI 16-18.5).
- And the third, while she has a "Normal" BMI of 23, doesn't look like she has much muscle - reminiscent of the "skinny-fat" body type we hear about a lot.

My take on the whole BMI thing is that unless you're a linebacker or a bodybuilder or someone with an obvious lot of muscle, you want to be under 30. If you're not an extreme endurance athlete you probably don't want to be much below 18. Between those values it's about % body fat relative to lean muscle.

Here's a blog post I once wrote about measuring body composition:

And here's one I wrote about tracking changes in body composition:

All of this sounds kind of ridiculous, considering my Spark ID, huh?
When I chose that ID, however, my own BMI was 52.6 and I would have been THRILLED to get it below 30. I'm not sure I ever actually believed it would get there, let alone under 25.

In fact, the technical medical term for a BMI between 18-25 is "Normal."

So I coined my OWN term "Healthy" to describe a BMI between 18-30. Because I can, and because it makes more sense to me.

So right now what I'm most concerned about is getting my body fat back under 19% because I feel stronger and more agile there. And I like how it looks.

That means moar lifting and lotsa nice lean protein, consistently over time.
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Member Comments About This Blog Post
    lower than 78% of women in the US, higher than 55% in the world

    most like the Netherlands

    Weird, I did it a second time and got lower than 77%, and most like Kazakhstan (same numbers and BMI), though on the chart, they are almost equal, too.
    2640 days ago
  • JIBBIE49

    2641 days ago

    Comment edited on: 7/24/2012 1:40:45 PM
    Boy this study really proves the U.S. is FAT!
    Here's my results:

    Your numbers
    Obesity Index
    BMI is an estimate of how "overweight" or "obese" a person is
    Below average
    You have a lower BMI than 74% of females aged 60-69 in your country
    Above average
    You have a higher BMI than 55% of females aged 60-69 in the world

    Did you know?
    If everyone in the world had the same BMI as you, it would add 30,759,671 tonnes to the total weight of the world's population

    SCARY THOUGHT. So even though I'm skinnier than most people of my age and gender in this country, I am fatter than most in the world! Very interesting! Oh--I didn't see this til I went back and looked. I'm most like a woman from France. Geesh, I don't even speak French!
    2642 days ago

    Comment edited on: 7/23/2012 3:49:31 PM
    Papua New Guinea! This is lots of fun . . . but I know that what really counts is per centage of body fat . . .

    Still, I'm happy NOT to be in the overweight or obese category of BMI, even though I agree it's body composition that really "counts".
    2646 days ago
    Liberia for me. I know BMI gets a lot of bad mouthing, but I worked hard to get into the healthy range, and for me it was one more goal and one more victory. I like seeing that my BMI is lower than 86% of females in my age group in the US and lower than 63% of females in my age group worldwide, and I want to keep it that way. As for body composition, I was doing strength training before I started losing weight, so I always knew there was good muscle mass under all my flab. Now I can see those muscles, and I'm thrilled!
    2649 days ago
    This was kind of fun to see. Thanks for posting it.
    2649 days ago
    I have a BMI lower than average for my age group. I'm most like someone from Hungary.

    It's kinda bittersweet that I have a lower BMI than 76% of women in my age group. On the one hand, it's great that I'm not above the curve. However, I'm only just on the high end of 'normal'. Just 5lbs would put me back into the 'overweight' bracket. That means most US women my age are overweight or obese.

    I'm a little higher than the global average currently, but I'm almost over the threshold of being the global 'average' or below.

    Despite BMI's flaws, it's nice to not fall into the 'overweight' bracket anymore.
    2649 days ago

    Comment edited on: 7/15/2012 10:56:34 PM
    I noticed the link on Facebook from you or another... and tried it for me, knowing fully well how high my BMI is! ...Strangely, I did not take the info as objectively as I thought I would.. :( I think it is the part that says, "If everyone in the world was as gigantically fat as you are, it would add 228,072,230 tonnes to the total weight of the world's population."

    I don't know.. I guess that although I know I have a long way to go still, it's ridiculously disheartening to see it spelled out like that.. as if I WANT it to be that way.

    Actually, it may just be that my company has put up signs in the bathroom about obesity, and the cost to the company in medical premiums, etc., that go along witht he 1st Lady's campaign, & I feel like all of my hard work doesn't make a difference in the eyes of the jerks that will judge me not on my healthy actions like eating well, or running, but solely on how I look. Grr.

    Sorry to make this all about me.. Love you, Ang, and I'm thrilled for you!
    2649 days ago
    East Timor for me....may have to check the globe! I've always taken BMI guideline lightly, since it really just doesn't account for body composition. But then bodyfat calculations can be so far off from one measurement mode to another, so I'm starting to think I really just need to go by how I feel and look...
    2649 days ago
    Heh. You're most like someone from New Zealand*.
    * Compared with other females aged 30-44 in New Zealand

    Wouldn't mind visiting and seeing if that equates to anyone of similar height and weight. =P

    I like measuring a wide variety of things. It's nice to be under 30 BMI, sure, but by combining that number with body fat (inaccurate, perhaps, but consistently so on my scale) and resting heart rate and inches and looking in a mirror I have a much broader picture of my overall condition.
    2650 days ago
  • OPTIMIST1948
    Hmm. I got Algeria.
    2651 days ago
  • MKELLY72
    Very interesting.
    I'm most like a woman my age from Pakistan.
    I'd like to find out what my fat percentage is with my BMI of 23
    2651 days ago
    I like watching the number on the scale and bmi chart go down, but what I am concentrating on is body fat %. I get it measured by a PT at the gym about every 8 weeks, and it is consistently falling. Now I just have to get this injury under control so I can get back to the ST. I never thought I would miss it so much!
    2651 days ago
    Maybe it should always be about body fat %? The problem with that is the means for accurate measurement are expensive. But I suppose you're right, if you're over 30, it's likely because you're fat. Under 30, you might be fat. hehe.

    Lift moar, lift HEAVY and eat lotsa protein. Pink dumbbells not allowed.
    2651 days ago
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