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To deny to the BMI is to deny logic

Updated on October 14, 2012

The BMI or Body Mass Index has become something of a controversial topic in the realms of health, fitness and weight loss. The controversy ranges from misunderstandings of what the BMI actually means and is supposed to indicate, through to full blown conspiracy theories - and I have read some truly ridiculous ones before now!

Here is the deal with the BMI.

It does not measure any of the following:

  • how active or fit you are.
  • how fat you are.
  • your worth as a human being.

That last point is ESPECIALLY important to remember, since there is a tendency these days for people to respond to what is essentially a medical diagnosis of being "overweight" or "obese" as a personal insult or judgement. I dare say the media is partly to blame for this with their constant scrutiny of any female celebrity who gains (or loses) a few pounds... but that is another issue to be tackled another day!

What the Body Mass Index actually does.

This is commonly confused so allow me to at least attempt to clear it up.

The Body Mass Index takes your weight, and compares it to what should be the expected weight for a human being of your height, gender and age under normal circumstances. I'll come back to "normal circumstances" later, but according to the Index there is a very wide range of around 15kg that is considered "normal". So, contrary to what is often alleged in internet blogs, we are talking about a range of weights that accounts for different body types and genetics, rather than an unrealistic pin-point "perfect" weight that people are required to be.

To reiterate; anywhere with this range of about 15kg is "about normal". Any less is "underweight", and any more is "overweight". And then beyond overweight you have "obesity". So if "overweight" could be seen as a little ambiguous, we have a category that translates to "ok, now you're actually more over weight than overweight". There can be no denying that this is a condition that should not occur under normal healthy circumstances.

Is it a bit out of date, though?

Yes, and no.

Remember a little earlier I talked about "normal circumstances"? Well, that's the issue. Right now we are NOT living under normal circumstances, and it has actually become normal to be overweight or even quite close to obese. Where "morbidly obese" used to be the relatively uncommon extreme weight category - literally meaning "in all likelyhood you will actually die of a disease you would probably not have contracted if not for being so obese" - we now have to come up with new categories since it has become quite common for people to reach sizes / weights that were previously unheard of. I'll say that again, these new categories did not exist previously because it was unimaginable for a human being to be this size / weight.

So, people have gotten bigger. But that doesn't mean that we should change our definition of what "normal" should be. When you watch some old movies or tv shows from the 70s or even early 80s, and you think "wow, look how thin everyone is!" - that's the size a human being is actually supposed to be. We're not talking about athletic physiques, or body builders cast as action heroes - just the average man, woman or child. They were more lean and slender than the majority of people today.

Even when there is a "fat" character in these shows, you'll see people twice that size in the street every day now. Things have changed!

Now this part is important so pay attention.

As I just said, 30 years or so ago the BMI would have been an accurate representation of the population, with most people falling into the "normal healthy" weight category.

Here's a list of stuff that not many people did in the 70s though.

  • Gym memberships, other than serious body builders.
  • Very Low Calorie Diets.
  • Meal replacement shakes.
  • Cutting carbs / avoiding bread.
  • Eating disorders.
  • whatever other lies you want to buy into about what's required to lose weight.

None of this stuff was very common at all back in the relatively recent times when most people fit into a healthy BMI. Rather, people just ate the appropriate amounts and had more active lifestyles.

Bottom line: these days we have unhealthy junk food too often, in portions that are too large. And we're not active enough. That's why people are fatter and heavier.

Back to the BMI though and applying some logic.

I think that was a lengthy enough response to the "but it is outdated" argument that people often use to disregard the validity of the Body Mass Index. Yes, people have gotten bigger, fatter and heavier, but not by natural evolution. Evolution would see us become stronger, leaner, and more fit for survival, not the opposite.

I'll attempt to address some other common arguments against the Body Mass Index that I have been subjected to recently.

  1. "But according to the BMI, some body builders or athletes who are quite lean would be classed as overweight".

    Indeed. As I said early on, the BMI is not a measure of how fat you are.

    It is entirely logical to expect an athlete who has deliberately trained to be stronger (due to more muscle mass) and more fit than the average human being, to weigh more than the average human being.

    As far as health implications go, being "overweight" due to super-human strength and fitness is fine. Being "overweight" due to carrying too much body fat though, not so much.

  2. "I exercise and stay active but according to the BMI I am fat".

    No. According to the BMI, your weight is higher than the normal range. This may or may not be due to carrying excess body fat despite leading an active lifestyle.
    The easiest way to tell is by looking in a mirror.

  3. "I'd like a weight loss plan to flatten my stomach, and tone up the backs of my arms and my thighs. But I'm not overweight, I don't believe in the BMI and besides, muscle weighs more than fat anyway. Actually forget it, you are a horrible, horrible man for judging me on how much I weigh instead of how nice a person I am".

    God has cursed me to endure this exact conversation at least once every couple of months, when I all want to do is help people so that they'll like me! Where do I even begin with this one?

    Logically, if you;
    (a) can visually identify areas where you are carrying excess body fat,
    (b) are not currently active and in particular are not performing strength training,
    (c) register as overweight or obese on the BMI, and
    (d) have actually asked for a weight loss plan...
    You are the one telling me where you need to lose fat from, but you're not really overweight and you're just carrying extra muscle mass despite not having trained to build it?

    Clearly there is no logic at all in this line of thought! And me being horrible is a separate issue entirely!

  4. That's ridiculous, if I lost that much weight I'd be nothing but skin and bone.

    Actually I managed to convince a nice lady otherwise when I pointed out that her friend standing next to her was taller (and therefore could be expected to weigh more) than her, but actually weighed less than the (maximum normal BMI) weight that I had suggested.

Bottom line: if you're overweight and not actually doing some serious muscle building training, the difference between your current weight and maximum normal BMI is a pretty accurate indication of how much excess body fat you are carrying.


How we conclude is entirely up to you.

You could decide "well, this guy is not very understanding and expects too much of people", but in actual fact you should feel EMPOWERED by the knowledge that all human beings (other than in relatively rare medical exceptions) ARE designed to fit into a particular weight range, and to get into this weight range does not require any unreasonable, over the top or extreme methods.

Simply put: appropriate meal choices and portion sizes, and a reasonable amount of physical activity.

It's only logical.


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    • profile image


      5 years ago

      Technically the BMI doesn't account for things lie bulk muscle which weights more than fat. So a lightly muscled person may seem over weight. What you're looking for is percent of body fat.

    • profile image


      5 years ago

      Awesome you should think of sohtmeing like that

    • personaltraining profile imageAUTHOR


      7 years ago from Melbourne, Australia

      thanks! My long term goal would see me in an obese weight range, but obviously with relatively low body fat percentage, fit, healthy and strong. In the photo above I would have been around 10kg (20lbs?) overweight, technically speaking.

    • Alphadogg16 profile image

      Kevin W 

      7 years ago from Texas

      Nice Hub. I definitely fall in the lean but still over weight category. At 6', 210 lbs, with 8% body fat, I'm suppose to weigh approximately 185 lbs according to the BMI.


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