The problem with body composition (bioelectrical impedance) scales

  1 Jan. 1 Feb. 1 Mar. 1 Apr. 1 June 1 July 1 August 1 Sept 4 Sept
Morning Weight: 65.5 kg 65.2 kg 63.5Kg 62.4Kg 64.2Kg 63.1Kg 63.8 Kg 63.4Kg 63.8Kg
Evening Weight: 66.5 kg 66.0 kg 64.6Kg 63.7 Kg 65.5Kg 64.9Kg 65.1 Kg 64.3Kg 64.5Kg
Morning Body Fat: 30.0% 28.0% 29.2% 26.6% 25.9%* 28.8% 28.1% 29.7% 28.0%
Evening Body Fat: 31.4% 30.4% 28.5% 26.1% 25.7%* 26.9% 27.6% 30.2% 26.8%
Bust: 33.5” 34.0” 34.0” 33.5” 33.5” 33.5” 34.0” 34.0”
Waist: 27.5” 27.5” 27.0” 27.0” 27.5” 27.0” 27.5” 27.0”
Belly: 32.0” 33.0” 32.5” 31.5” 32.0” 31.0” 31.5” 31.5”
Hips: 40.5” 40.5” 40.0” 39.5” 40.0” 39.0” 40.0” 39.5”
Thigh: 24.0” 24.0” 23.5” 22.5” 22.5” 23.0” 23.0” 23.0”

I had a serious problem with accuracy when I weighed and measured myself on the first of September. I use a Tanita InnerScan scale, which uses bioelectrical impedance to measure body composition. Body composition is simply the percentage of fat, muscle and bone that make up your body. Essentially, a small electric current is run through the body, moving at different speeds through muscle and fat. Sadly bioelectrical impedance is hugely influenced by hydration levels – my body fat can change by up to 3% between first thing in the morning (dehydrated) and last thing at night (fully hydrated).

Apparently I was massively dehydrated on Friday, as despite my lower weight and smaller measurements, it was showing my body fat had gone up between 1.6 and 2.6%! As my weight hadn’t gone up, this is only possible if I had lost muscle mass. However, I’m still hitting the gym regularly and continue to get stronger (slowly) so I really doubt this is the case. As it happens, my husband and I had celebrated the end of the week with cheese, pate and a bottle of red wine. Normally I’m quite careful to drink plenty of water with my wine, but apparently I neglected the water on Friday evening, which could be why my body fat was way up!

Just to make sure I wasn’t imagining things, I reweighed myself in both the morning and evening yesterday. And no, I didn’t spend the weekend crash dieting. As anticipated, yesterday’s body fat values were much closer to the ones I’d had at the start of August.

Moral of the story: Unless you are measured by a BodPod or DEXA scanner in a lab, take all body fat measurements with a pinch of salt! Good thing I have my next BodPod appointment on Monday to see where we really stand.



*Dubious values as I was not using my own scale.

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