My oh my, BMI


Stormy (Robyn) is a geek, feminist and Physical/Health Educator (B.S./M.S. Ed) living in the USA. She offers health coaching for geeky girls through Follow her on instragram and twitter @geekgirlstrong

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  • Stormy, this is fascinating. Thanks for writing about this.

    Semi-related question, what’s with the scales that show your water retention and fat percentage? How can they do that???

    • Hi Hadas,

      Sorry it took my so long to respond. Just saw that the blog was up and running again! I also wanted to make sure I gave you a fleshed out response (I didn’t mean for it to be a pun, but it works).

      Thanks for your question, it’s totally related.

      Those scales use what is called Bioelectrical Impedance Analysis (BIA). BIA works by measuring the resistance in passing small amounts of electrical currents through your body’s tissues. The unnoticeable current goes up one leg, through the body, then down the other leg. Those currents move slower through fat and faster through your muscle. The scale takes those readings and uses a programed formula to give your body fat percentage.

      It’s pretty cool , but all signs point to them not working very well or even at all. They are very iffy, the scale has to be placed on the right flooring, the results can be altered by your body temperature, having wet (or just sweaty), dirty or calloused feet, how much water you recently had to drink, your body’s shape, and more.

      If you or anyone else is interested in having a more reliable reading of their body composition, there are methods that are trusted: hydrodensitometry (underwater weighing, usually considered to be the most accurate), the Bod Pod (you sit a in Pod and instead of displacing water in a tank, you displace the air in said pod. I did this college as well) and DEXA scans (a type of X-ray).

      I hope I answered your questions well enough!
      Let me know if there is anything else I can help with.

      In good health,