Body composition testing

Jthanmyfitnesspal
Jthanmyfitnesspal Posts: 3,580 Member
edited November 2024 in Fitness and Exercise
A recent post mentioned Bod Pod, which I have been hearing about lately, so I did a little digging. Let me say that my background is in physics, not physiology, but I think body composition is an interesting topic. Here are my observations:

Various advanced (expensive) techniques exist for assessing body composition, including DEXA and QMR. These offer high accuracy, but are overkill for non-medical routine use (e.g., by aspiring athletes, dieters, etc.)

Hydrostatic weighing (HW) has been used for many years as a lower-cost method. More recently, Bod Pod has popularlized air displacement as an alternative. Both methods are able (with some degree of accuracy) to determine mean body density from which %BF is derived by formula.

Various sources (particularly those charging you money) quote very high (as small as 1%) accuracy for these methods. I see one paper mentioning that different operators may get significantly different results (as high as 5.5%) for the same subject using the Bod Pod (Am J Clin Nutr 2002;75:453–67), so the 1% accuracy claim may be understated.

I conclude as a non-expert that the very-low-cost methods are likely accurate enough for most people. These include hip-to-waist and skin-fold analysis. The costs of these is peanuts compared with Bod Pod.

Note that I am not very impressed with bioelectrical impedance, which varies with how much sweat is on your skin and many other factors.

I'm interested to hear other opinions.

Replies

  • stanmann571
    stanmann571 Posts: 5,727 Member
    While overall accuracy is relevant, It's largely irrelevant.

    What's more important and useful is trend and consistency.

    So even if you're not impressed by BIA, as long as you replicate conditions from session to session the trend will be meaningful and useful
  • pogiguy05
    pogiguy05 Posts: 1,583 Member
    I actually did the bodpod and I forgot where I put my results print out now that you mention it. At least for me it came with 2 scans and I have yet to use the second. I probably will once I reach my goal weight. I also have one of them Skulpt Chisels and I have used it a couple of times. I know they are not probably that accurate and with Skulpt you really need someones help for the full body cause there is no way you can get the upper and lower back measurement properly.

    However, they are just tools just as my fitbit ionic and the gym. What matters is my commitment to eating healthier and exercising. Plus they way I look and feel. I am just trying to turn back 25 years of neglecting myself.
  • Azdak
    Azdak Posts: 8,281 Member
    All body fat assessment methods are estimates of an estimate. They also all have issues with methodology, even those that are the so-called “gold standard”. Like stanman571 said, consistency of testing conditions and trends over time are probably the best way to use BF measurements.

    We use an InBody 570, which is a sophisticated BIA machine. From what I can tell, it probably underestimates body fat by 2-3 percentage points. However, under standard testing conditions, I have found that measurements over time accurately reflect physical changes.
  • sgt1372
    sgt1372 Posts: 3,997 Member
    OP: You've stated your negative opinion about the cost of BF methods elsewhere.

    My DXA scans only cost me $45 ($40 if I wanted to pkg of 4 or more; I don't). Hydro cost me $49 for the 1st test a yr ago and has cost $39 for retests ever since then. That's not expensive for me.

    DXA provides information, like VAT and bone density that cannot be measured by any other means. I only do hydro as a basis of comparison w/DXA but I don't think doing either for such cost is "overkill" in terms of monitoring my weight and BF.

    If I could not afford it, I certainly wouldn't do it as often as I do but, as a diagnostic tool, I think that everyone should get a baseline DXA scan and get another scan annually thereafter at the same time that they get their annual physical examination and blood tests for a more detailed health assessment.

    As for the BodPod, it is considered among the least accurate and reliable methods of BF measurement, along w/bioelectrical scales and other devices.

    On the othe hand, calipers, while cheap, are only as good as the person using them and few people are trained to use them accurately. If you can a person who is properly trained in taking skinfold measurements, great, but you have to find such a person because you cannot take all of the skinfold measurements (at least 7) necessary to get a precise result by yourself and you may have to pay for that service as well.

    As for the 2x waist to height indicator, like BMI, this is not a measurement of BF in itself. If you do not need or want to put a specific # on it because you consider it too costly and/or imprecise, fine, you don't have to do so, but some of us prefer greater specificity in monitoring our health and BF and are willing to pay the cost for that.
  • Jthanmyfitnesspal
    Jthanmyfitnesspal Posts: 3,580 Member
    @sgt1327 I'm amazed you can pay so little for DEXA (or DXA)! I assumed it would be much more expensive than that. I see a deal in Massachusetts to get it for about $175, which still sounds pretty reasonable.

    I respect anyone's decision on this, but, aside from the cost, there's the issue with DEXA of requiring full-body x-ray exposure. That seems excessive (to me) just for determine %BF for the purposes of fitness assessment. (Again, there are low-tech approaches that seem good enough to me.
  • fuzzylop72
    fuzzylop72 Posts: 651 Member
    edited November 2017
    I think dxa scans vary in price widely. The ones near me are 150 per test unless you buy a 4 or 8 pack. The lowest they cost me is 65 (additional scans beyond the 8).
  • BusyRaeNOTBusty
    BusyRaeNOTBusty Posts: 7,166 Member
    Does the number REALLY matter that much anyway? I know what I see in the mirror. I know what others see. That's good enough for me.

    A while back I had calipers done, came up with 19%. I also did a handheld, 23%, and a stand-on weight scale, 36%. Visually, comparing myself with those posted pictures, I think I was somewhere around 25% so the hand held was closest.
  • sijomial
    sijomial Posts: 19,809 Member
    BusyRaeNOTBusty wrote: »
    Does the number REALLY matter that much anyway? I know what I see in the mirror. I know what others see. That's good enough for me.

    I agree with this. Once you are close to goal weight the mirror is fine. Personally I like myself around "2 pack" level of leanness - whether that happens to be 13, 15 or 17% I'm really not bothered. Especially as the number you get is often subject to a significant margin of error.
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