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Tuesday, 18 February 2020

Biorythms and body fat percentage readings

To smooth out the daily 'noise' in the body fat percentage readings that I get each morning using my bathroom scales (there can be +-2% fluctuations from day to day!) I calculate a 21-day moving average of the body fat and weight readings to better track my overall progress (between getting more accurate DEXA readings of my body fat). For the single DEXA reading I obtained so far, the 21-day average of body fat readings from my bathroom scale was very close to the value provided via DEXA.

Aside from the slight weight increase that occurred due to overeating over the Christmas holiday period, the plot of average weight vs. elapsed days shows a steady decline, with the rate of weight loss increasing since I changed from a 'balanced' caloric restriction diet with intermittent fast days, to adopting a high protein/fat 'keto' diet plan earlier this year. This is to be expected, as you are going to consume (loose) body fat over time if you are ingesting fewer calories than your basal metabolic rate, especially when caloric requirement is also increased by doing additional physical activity such as walking and weight training. Weight training also helps maintain metabolic rate, which might otherwise reduce (hence reducing caloric requirements) in response to sustained caloric restriction. Over a period of 100 days my average weight reduced from around 101 kg to around 86 kg (a weight loss rate of about 1kg/wk)

However, the plot of the 21-day moving average of body fat readings shows a distinct cyclical pattern overlaid on the overall downward trend, with a periodicity of roughly 30-days. It can be quite disconcerting to encounter these 'plateaus' in body fat reduction, as it means I experience several weeks of quite noticeable decreases in body fat (yay!), only to be followed by several weeks of stable (or slightly increasing) body fat readings (d'oh!), despite sticking to my diet and weight training routine.

I used an online 'biorhythm calculator' to plot the three theoretical biorhythms (physical, emotional and intellectual) and compared it to the cyclic fluctuations in my average body fat readings. It appears that there may be a monthly fluctuation in body fat percentage - or at least in the readings produced by the bathroom scale's bioelectric impedance measurements, which are known to be affected by hydration.

I'm currently in the stable/upward part of the cycle in body fat readings, which seems to be 'stuck' around 17% at the moment. This means that my calculation of lean mass and body fat (derived from my weight and body fat percentage) suggests that I'm losing lean mass and not losing any fat at the moment (which doesn't make sense as I'm losing weight at a fairly modest rate and doing weight training to retain lean mass as much as possible). Hopefully this is simply an artifact due to the 'monthly cycle' in hydration that is affecting the body fat readings produced by my bathroom scales, and I should start to see lower readings over the next week or two. The fact that the skin fold thickness over my abs seems to be reducing would also suggest that I am still reducing body fat, regardless of what my bathroom scales are saying! It would be nice to be able to get accurate skin fold thickness measurements to calculate body fat, but the skin-fold calipers I ordered online several months ago never turned up.

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