Step on the scale two mornings in a row and the number can move by a kilo without anything real changing. Actual fat change is slow. Even in a fairly aggressive deficit it is a fraction of a pound a day, so most of what you see is water and what's in your gut.
Where the noise comes from
- Glycogen and water. Each gram of stored carbohydrate holds roughly three to four grams of water. A higher-carb day can add a kilo or two of scale weight within days.
- Sodium and travel. A salty meal or a long flight shifts fluid for a day or three.
- Bowel contents. Hundreds of grams, depending on what and when you ate.
- Menstrual cycle. About half a kilo on average, covered here.
The fix: a moving average
An exponentially weighted moving average gives recent days more weight than old ones, so a single odd reading barely moves the line. John Walker popularised this for weight in The Hacker's Diet, using a smoothing factor of 0.05, which works out to roughly a three-week window. That factor is a convention, not a proven optimum. A seven-day average is a reasonable simple alternative.
How to use it
- Weigh yourself at the same time each day, ideally in the morning.
- Ignore the daily number and watch the trend line.
- Judge progress over two to four weeks, not days.
PixelPT's nutrition targets are driven by the trend, which is why a bad weigh-in doesn't cut your calories.
References
- Walker J. The Hacker's Diet. 1991. fourmilab.ch.
- Peos JJ et al. Med Sci Sports Exerc. 2021 (diet-break water and glycogen effects on body weight).
This is general information, not medical advice. See the health disclaimer.