Consensus on BF% scales' consistency?

Micah_Johnson
Micah_Johnson Posts: 22 Member
edited December 4 in Health and Weight Loss
Given the threads I've read here on MFP, as well as reviews of top-dollar "smart scales" like the Fitbit Aria and the Under Armour Healthbox, it seems that the consensus is that BF% measurements on most floor scales are wildly inaccurate. My question is, are they consistent? In other words, I wouldn't mind if the scale showed my BF% inaccurately at 30%, as long as it would consistently show an actual 5% drop in my BF% as a 5% drop on the scale.

I ask because I'm trying to build muscle mass as I lose weight, and as such, I worry that raw changes in my weight do not accurately reflect my progress. If I could consistently monitor changes in my BF% from home, that would be worth the price of an Aria to me.

As always, thanks for the insight from any folks replying.

Replies

  • HealthyBodySickMind
    HealthyBodySickMind Posts: 1,207 Member
    I think you may have some confusion on BMI v. BF%. This article may give you some ideas on how to measure: https://www.nerdfitness.com/blog/2012/07/02/body-fat-percentage/

  • Micah_Johnson
    Micah_Johnson Posts: 22 Member
    You're right. I'll see if I can edit the OP.
  • stevencloser
    stevencloser Posts: 8,911 Member
    Those scales are pretty inaccurate, in that they can jump something like 5-10% within a single day even, depending on stuff like your hydration level.
  • tcunbeliever
    tcunbeliever Posts: 8,219 Member
    I have an omron handheld, it's very consistent if I measure naked first thing in the morning with my arms in the same position.
  • MaggieLoo79
    MaggieLoo79 Posts: 288 Member
    My Aria is inconsistent. In the afternoons, when I'm the most hydrated, my body fat could be up to 2.5% lower than it was that same morning. I use the back up tape measure method from the Navy (I think). If you google body fat and Navy, the formula comes up. I use my Aria every day, but I do the tape measure calculations once a month as back up. I have a hard time seeing trends in the Aria - especially since it doesn't do averages. My fitbit gives me an average weekly weight, but not an average weekly body fat, which makes it very hard to tell if I'm moving in the right direction. I still like the Aria because it automatically records my data, but, like I said, I use measurements to double check the body fat.

    Oh, and the tape measure method I use has my body fat 1% higher than the Aria says. I hope that helps.
  • CattOfTheGarage
    CattOfTheGarage Posts: 2,745 Member
    The whole idea of body fat scales is baffling to me. The only way you can measure body fat (short of MRI or dissection) is by measuring your volume displacement and using that to calculate your density. You can then infer from that number how much of you is fat as opposed to heavier substances like muscle, bone, innards etc. Even that calculation has to be super precise to get a reasonably accurate answer, as fat is only slightly lighter than the other ingredients.

    So how can a scale do it? How can it even make a rough estimate? In the face of it, it makes as much sense as saying you have a set of kitchen scales that doesn't just tell you how many grams of cake mix you have, but how many eggs are in it. My best guesses for how this works are (a) witchcraft or (b) marketing nonsense.

    I have no idea of the answer to your question, OP, but given the above I'm going to take a stab at "no". I am, of course, open to correction as ever.
  • AnvilHead
    AnvilHead Posts: 18,343 Member
    A worthwhile read on the topic:

    http://weightology.net/weightologyweekly/index.php/free-content/free-content/volume-1-issue-4-the-pitfalls-of-body-fat-measurement-parts-3-and-4-bod-pod-and-bioelectrical-impedance-bia/the-pitfalls-of-bodyfat-measurement-part-4-bioelectrical-impedance-bia/
  • mburgess458
    mburgess458 Posts: 480 Member
    stevencloser wrote: »
    Those scales are pretty inaccurate, in that they can jump something like 5-10% within a single day even, depending on stuff like your hydration level.

    This is my experience with a couple of different scales. They will read from 8% to 20% depending on time of day and what I have eaten/had to drink recently. I had a BodPod measurement done and it was somewhere in the middle of that.

    So to answer the original poster... no, they aren't at all consistent.
  • Micah_Johnson
    Micah_Johnson Posts: 22 Member
    Well, that's all remarkably disappointing, but it's good to know.
This discussion has been closed.

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