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I've been going to the gym around 3 - 5 times a week for 2 solid months now. I do a variety of weight training exercises and up to 20 minutes of running on a treadmill. I have a fairly balanced diet and consume a lot of protein through solid food and shakes.

After my first month of training, I decided to pay to use the electronic weighing machine at my gym. After analysing the print out from the machine I noticed that my BMI is above what it should be.

Today I used the electronic weighing machine again to see if my BMI had gone down. To my surprise, it had gone down by 0.1% - I wasn't sure if I should be happy about this or not as it's not really that much of a difference.

Results comparison:

https://scontent-b-lhr.xx.fbcdn.net/hphotos-prn1/t1.0-9/14560_10202863048912502_829773703_n.jpg

enter image description here

I have suspisions that the machine is reading my height incorrectly, so I really don't know if I should trust this machine or not.

Should I really care about my BMI? I'm losing fat and gaining muscle (from what I understand from the results), so what's the deal breaker here as my BMI is still over :(

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    Did you use the same machine in both measurements? You seemed shorter in the newer result.
    – Kneel-Before-ZOD
    Commented Mar 24, 2014 at 0:51
  • Yes exactly the same machine. Both measurements were taken post workout too. I'm sure the height thing is down to not standing up with a good posture, but still. I actually got somebody else to measure my height a few weeks ago and I stood close to 5 foot 7. I'm really not sure what to think of these results.
    – Joel Murphy
    Commented Mar 24, 2014 at 1:03
  • @Kneel-Before-ZOD Squats compress your spine bro. I read it in an article somewhere.
    – user2861
    Commented Mar 24, 2014 at 4:00
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    No, BMI is pure BS. I was 250lbs and 7% bodyfat and I was morbidly obese when I went to my company's health evaluation (back in the day). I said, "yep, I'm dead."
    – Dan Andrews
    Commented Mar 24, 2014 at 20:35
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    Please see @Kneel-Before-ZOD answer. We will agree to disagree at this point. I think it's total BS for healthy people.
    – Dan Andrews
    Commented Mar 27, 2014 at 2:03

4 Answers 4

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A difference of 0.3" (a little more than a quarter of an inch) is within acceptable measurement error on something like this.

The answer to your question is:

BMI does not matter for individuals

A perfect example for the reason why is with the two tickets you included in your question:

  • On Mar 4 2014 you had BF% of 16.2% and BMI 25.5
  • On Mar 23 2014 you had BF% of 13.3% and BIM of 25.4

With a difference of only 1 kg of body weight, that's a rather impressive transformation. Congratulations! Problem is the BMI didn't reflect the hard work you put in.

BMI was designed as a statistical device to determine the average obesity of a population. It was never intended to be applied specifically to a population of one. The problem is that body fat is very difficult to measure or even estimate (accurately), and BMI requires only junior high school math skills to calculate.

Unfortunately insurance companies and doctors tend to use this simple measure because it really doesn't require any thought. They are just trying to determine risk, and for most people BMI is good enough.

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BMI simply measures the relationship between your weight and height and doesn't care if the weight is muscle-based or fat-based.

You're focusing on the wrong thing: your body fat in the first measurement was 16.3% and it changed to 13.3% in the second. The second value fell within the range of your ideal body fat.

You also lost over 2-kg in body fat, all within two weeks.

That's a big improvement! And you should certainly continue what you've been doing as it clearly works.

If the BMI value bothers you so much, try another machine after another two weeks. However, you shouldn't worry much about it because your body fat percentage is much more important than your BMI and that's going down.

Congratulations on burning the goo. Now, go burn some more :).

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  • " 2-kg in body fat, all within two weeks" .. "you should certainly continue what you've been doing". Hmm, at this rate he'll be in the underfat range within two months. So I wouldn't call it 'great progress'. He'dd better start eating more calories so he doesn’t overshoot his goals IMHO.
    – Pibara
    Commented Mar 26, 2014 at 18:40
  • @user1703394 If he's following the plan highlighted above, he's unlikely to overshoot his goals. Once the fat level is greatly reduced, the protein's effect of building his muscles should allow him to bulk up. At least, that's what should happen. :)
    – Kneel-Before-ZOD
    Commented Mar 26, 2014 at 18:45
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One possible explanation for the height discrepancy: consider that throughout the day, your precise height is not constant. In the morning after you wake up, you are actually slightly taller than you are in the evening when you go to bed. Another explanation is variability in posture, as well as measurement imprecision.

As has been mentioned elsewhere, BMI is not a suitable diagnostic measure for medical problems. Its simplicity and ease of calculation, however, has resulted in its widespread use as a proxy for medical conditions (e.g., in insurance underwriting). The more important measure in the printout you have is the body fat percentage--in fact, it is this value that is what BMI was originally intended to correlate with (but this correlation is weak).

Also bear in mind that body fat percentage can be measured and calculated in a variety of ways, and certain methods are imprecise, inaccurate, and/or unreliable. Bioelectrical impedance analysis is less accurate than hydrostatic submersion. Given the numbers in the printout, it is unlikely that the body fat percentage was calculated from the BMI (this, of course, is a wildly inaccurate method and is almost meaningless).

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First, your BMI is something you can safely ignore given that you have ways to determine your body fat. BMI is an easy 'statistical' tool for getting rough 'population' obesity numbers. BMI for individuals does not have a dependable relationship to obesity and/or to obesity related health issues. Your body fat percentage is what matters, and looking at that, you are at a great level there, and at this stage you should actually not allow it to go down much more.

Going from these two measurements, you've lost an amount of body fat equal to 3% of your body weight in less than 3 weeks. At that rate you will be in the under-fat range very soon, and that will mess up your hormone levels in such a way that you will likely feel it in your power stats. First, these are just two measurements, so keep measuring, but if this trend continues and you continue loosing fat at this rate, you need to seriously look at your diet and take in considerably more calories to avoid disaster.

So don't listen to the comments above stating these numbers show you are on the right track, if you continue at this rate you will end up somewhere you definitely don't want to be, at least not at this stage. Its way to early to think about getting a ripped beach body, you should gain strength and mass first, so in a year or so (2 or 3 years would be even better) you may want to consider getting ripped occasionally. For now, don't let your body fat get below something like 10% and focus on strength. Forget about doing cardio for now, go strength first untill you are convident all your muscles are in good shape and at acceptable strength levels. Only than you may want to loose a few more percent, but even than 7% should probably be the lower limit.

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