Is BMI an accurate way to know how much I should weigh?

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  • janejellyroll
    janejellyroll Posts: 25,763 Member
    AnnPT77 wrote: »
    ...
    Sure, BMI is good for a lot of people. But why rely on a metric that only considers height and weight? Why not try, e.g. the Navy's method of estimating body fat percentage? It uses gender, height, weight, waist circumference, hip circumference (for women), and neck circumference. All easy to do. Just my opinion.

    I don't know what I said in the above quote that prompted several people to click Disagree.

    Do you disagree that "BMI is good for a lot of people"?
    Do you disagree with my suggestion to try the Navy method? Or that it's "easy to do"?

    My problem with BMI is that in order to cover most people, it has to have a fairly broad range of BMI categorized as Normal. It is flawed logic to think this only results in some "outliers" appearing to be overweight (or underweight). Those that are "outliers" would include not only those who are normal but fall outside the normal BMI range, but also those who are not normal but appear to be, i.e. too fat but have a normal BMI, or too skinny but have a normal BMI.

    I knew a woman years ago that clearly had a self-image problem (probably had anorexia). I wonder if her BMI did or would have told her she's in the underweight category. Hopefully so.

    So disagree as you will, but I don't care much for BMI, and as Shakespeare said in Much Ado About Nothing, it is an "opinion that fire cannot melt out of me. I will die in it at the stake." :smile:


    Digression from OP, but: No point in worrying over disagrees, at least unless/until there are a bunch on one post, anyway (and maybe even then, if it makes no sense on reconsideration). Sometimes people hit the "disagree" accidentally when thumb-scrolling on a phone; some people disagree with pretty much any post on the opposite side of any hot-button topic (like BMI); some people lack reading comprehension and misinterpret; posts that mention "disagree" tend to draw disagrees because people consider themselves jokesters; sometimes if one hacks off a person on some other thread (or earlier in the current one) they'll disagree on any post they see from you until they get over their tantrum; more.

    None of it worth consideration, IMO, for anyone with reasoned convictions and adequate ego-strength. If they can't use their words to explain, and the back-thread provides no insight . . . might as well let it go, or it can drive a person crazy. 😉

    For clarity: I didn't disagree with your PP, click-wise or otherwise. I do agree with Jane's perspective on it, though: Don't understand why people are so wrought about BMI, unless they don't like their own number and somehow take it personally. It's just a screener, not intended to be individually definitive. When insurance companies or the like use it (without a better individualized fallback measure) in rate-setting or some other matter of consequence, that's worth getting angry about. Otherwise, who cares?

    And for the record, I do oppose anyone using BMI as a single point of determining data without taking anything else into account (I know you weren't saying otherwise, just wanted to make that clear).
  • frankwbrown
    frankwbrown Posts: 12,044 Member
    @annpt77 and @janejellyroll
    No worries!
  • Theoldguy1
    Theoldguy1 Posts: 2,428 Member
    azalea4175 wrote: »
    Getting a bod pod is the way to go in order to understand how much of your body weight is fat. Height/weight ratios are pretty worthless. IMO, anyway. I only pay $40 for a bod pod test and it shows me every 6-8 weeks how much fat I’ve lost and how much lean muscle mass was gained. What good is losing 15 pounds if 10 of those are muscle mass? I yo-yo’d a lot with losing muscle mass whenever I lost weight until I started using that testing method.

    Where does one find a "bod pod"? I am pretty sure such a thing is not available to us....have I mentioned I live practically at the end of the earth in Maine? :)

    Google Bod Pod Maine and see what you come up with.
  • kimny72
    kimny72 Posts: 16,023 Member
    edited December 2020
    NM :smile:
  • kimny72
    kimny72 Posts: 16,023 Member
    azalea4175 wrote: »
    Getting a bod pod is the way to go in order to understand how much of your body weight is fat. Height/weight ratios are pretty worthless. IMO, anyway. I only pay $40 for a bod pod test and it shows me every 6-8 weeks how much fat I’ve lost and how much lean muscle mass was gained. What good is losing 15 pounds if 10 of those are muscle mass? I yo-yo’d a lot with losing muscle mass whenever I lost weight until I started using that testing method.

    Where does one find a "bod pod"? I am pretty sure such a thing is not available to us....have I mentioned I live practically at the end of the earth in Maine? :)

    It really depends on the area. I've never managed to live anywhere that a reasonably priced bidpod was within a 50 mile radius. :disappointed:
  • frankwbrown
    frankwbrown Posts: 12,044 Member
    azalea4175 wrote: »
    Where does one find a "bod pod"? I am pretty sure such a thing is not available to us....have I mentioned I live practically at the end of the earth in Maine? :)

    Check with universities and/or professional athletic organizations in your area. They often will have some means of body composition testing.

    I was looking into getting a bodpod-based assessment, and realized I'd have to travel some distance for that. Then I learned of a company that had mobile DEXA units. I was able to meet one of those vans ~64 miles away. I did that on Sept 30th, and I'm having a 2nd scan on Dec 20th. I feel doing this every 3 months or so is worthwhile for me personally, at least until I am down to the weight I want to be.

    A much cheaper alternative to DEXA or BodPod is getting a weight scale that measures body fat. They won't be as accurate, but the decent ones aren't any worse than BMI. I've seen them range in price from less than $30 to over $300. Many support bluetooth so you can capture your measurements in an app. I purchased a Withings Body+ for $79 and have been very happy with it. It takes me 2 minutes to copy my weight, body fat %, fat mass, lean mass, etc. into a Google sheet.

    I understand many will say I'm going overboard and that BMI and common sense is all you need. To those I say, "You do your thing, and I'll do mine."

    I fully admit that as a retired programmer, I tend to obsess a bit about data.
    This is a chart that is updated daily when I enter each day's data.


  • Theoldguy1
    Theoldguy1 Posts: 2,428 Member
    azalea4175 wrote: »
    Where does one find a "bod pod"? I am pretty sure such a thing is not available to us....have I mentioned I live practically at the end of the earth in Maine? :)

    Check with universities and/or professional athletic organizations in your area. They often will have some means of body composition testing.

    I was looking into getting a bodpod-based assessment, and realized I'd have to travel some distance for that. Then I learned of a company that had mobile DEXA units. I was able to meet one of those vans ~64 miles away. I did that on Sept 30th, and I'm having a 2nd scan on Dec 20th. I feel doing this every 3 months or so is worthwhile for me personally, at least until I am down to the weight I want to be.

    A much cheaper alternative to DEXA or BodPod is getting a weight scale that measures body fat. They won't be as accurate, but the decent ones aren't any worse than BMI. I've seen them range in price from less than $30 to over $300. Many support bluetooth so you can capture your measurements in an app. I purchased a Withings Body+ for $79 and have been very happy with it. It takes me 2 minutes to copy my weight, body fat %, fat mass, lean mass, etc. into a Google sheet.

    I understand many will say I'm going overboard and that BMI and common sense is all you need. To those I say, "You do your thing, and I'll do mine."

    I fully admit that as a retired programmer, I tend to obsess a bit about data.
    This is a chart that is updated daily when I enter each day's data.


    Have you compared a DEXA scan to the Withings scale? We have an older scale and it isn't worth the powder to blow it to hell regarding getting a reading similar to DEXA scan.
  • frankwbrown
    frankwbrown Posts: 12,044 Member
    Theoldguy1 wrote: »
    Have you compared a DEXA scan to the Withings scale? We have an older scale and it isn't worth the powder to blow it to hell regarding getting a reading similar to DEXA scan.
    Yes. Here is a comparison:

    A = Withings Body+ (9/30 at 6:10 am);
    B = DEXA scan (9/30 at 11:30 am)
    body fat: A = 49% , B = 44.5%
    weight (lb): A = 304.9, B = 305.0
    fat mass (lb): A = 150.8, B = 135.6
    lean mass (lb): A = 154.1, B = 169.4 (159.9 excluding bone mass)
    water mass (lb): A = 125.8, B = n/a
    bone mass (lb): A = 7.6, B = 9.5
    BMI: A = 40.4

    Bioelectrical impedance isn't that accurate, especially when only feet are involved (vs feet and hands).
    I use it primarily to confirm that I'm losing fat mass and not lean mass.

    Some doctors at Cedars-Sinai developed an alternative to BMI. It's called Body Fat Mass Index.
    Relative Fat Mass Index:
    Men: 64 – (20 x height/waist circumference) = RFM
    Women: 76 – (20 x height/waist circumference) = RFM
    https://www.cedars-sinai.org/blog/relative-fat-mass.html
  • DBGittings
    DBGittings Posts: 3 Member
    ninerbuff wrote: »
    If you don't have a lot of muscle, then it's okay. But you could also be very "skinny/fat" and be within the BMI level for your height and weight.

    A.C.E. Certified Personal and Group Fitness Trainer
    IDEA Fitness member
    Kickboxing Certified Instructor
    Been in fitness for 30 years and have studied kinesiology and nutrition

    9285851.png

    Exactly. I am 225 lbs and my bmi is 33 but when I was at 170 lbs, I looked like a bobblehead. This definitely isn't a one size fits all type of scenario.
  • DBGittings
    DBGittings Posts: 3 Member
    Mellouk89 wrote: »
    You don't need to be on the level of an “elite” bodybuilder, if you've been lifting for a year or more you will develop a lot of muscle mass. Most of your gains will occur in the first year assuming you eat right and train hard. If you have gained 20lbs of muscles in your first year, then BMI is unreliable.

    As i've said, I have a 32.5 inch waist at a BMI of 24.2, if I gain 4 more pounds i'm officially in the overweight category. And that's just me doing bodyweight exercises for the past months, it doesn't take much

    And i'm not even going to delve into the subject of gender and different ethnicities.

    Exactly!!!! I agree 400%
  • Mellouk89
    Mellouk89 Posts: 469 Member
    edited December 2020
    It may be more than a year for some people but the point is its not hard to gain muscle mass assuming you're fairly young and have normal levels of testosterone. Stop focusing on the one year part, gaining muscle mass is not that hard for most men.

    I've been around young people who lifts, they put muscle mass on without even trying.

    If you're over 40, it's a different ball game.
  • Mellouk89
    Mellouk89 Posts: 469 Member
    edited December 2020
    Here we go with the disagree spam, have you noticed that I said a year OR MORE in the post he just quoted? It might take more than a year, but look at the bigger point. Gaining muscles while young is relatively easy, even if it's just 10-15lbs of muscles it's enough to put you “slightly” out of the normal range. Meaning a bmi of 26-27.

    And for some reason people are fixated on bmi, when I mention waist to height ratio or other measures people start spamming disagree.
  • J72FIT
    J72FIT Posts: 5,958 Member
    edited December 2020
    Question about waist to height ratio. How do you guys measure your waist? Fully relaxed mine is 36". Fully relaxed with all the air blown out it is 35.5". Flexed (not sucked in) it's 33.5" What to do...? I weigh 178lbs at 5'10". According to BMI I am overweight.

    Note: when I weigh 175lbs all measurements come down 1/2 inch. For my height, I think 174lbs is the cut off for normal bmi...
  • Mellouk89
    Mellouk89 Posts: 469 Member
    edited December 2020
    First thing in the morning, I measure right at the belly button and fully relaxed with the air blown out. As long as you measure your waist relaxed and you don't flex or suck in.

    Edit : It's also good to point out that is you do weighed ab exercises, or you do hypertrophy based exercises for abs your waist size might increase in the process.
  • Theoldguy1
    Theoldguy1 Posts: 2,428 Member
    J72FIT wrote: »
    Question about waist to height ratio. How do you guys measure your waist? Fully relaxed mine is 36". Fully relaxed with all the air blown out it is 35.5". Flexed (not sucked in) it's 33.5" What to do...? I weigh 178lbs at 5'10". According to BMI I am overweight.

    Note: when I weigh 175lbs all measurements come down 1/2 inch. For my height, I think 174lbs is the cut off for normal bmi...

    I've had this done by different nurses in a doctor's office several times. The measurement is taken fully relaxed.