Accepted answer
16 weeks is 112 days, and the only question is whether 16 weeks accumulates more signal than the instrument's own noise. Scan-to-scan precision on lean mass is about one to one and a half per cent under standardised conditions, so on a 60 kg lean mass the least significant change is roughly 0.9 kg. At half a kilogram of total loss a week with a quarter of it lean — 0.125 kg of lean per week — 16 weeks accumulates 2 kg. 2 kg clears the 0.9 kg threshold, so a repeat every 16 weeks resolves a real change rather than reporting its own error. That is the interval to use. Standardised means the same machine, the same time of day, the same hydration state, the same clothing. Change any of those and the precision figure this arithmetic rests on is no longer yours. Three scans on a line beat two scans and a difference at any interval: the third is what tells you whether the second was a measurement or an outlier.
On the detail: this is an instrument question rather than a physiology question, and treating it as one resolves most confusion in this tag.
Radiation exposure is very low — of the order of a few microsieverts, comparable to a day or two of natural background — so scan frequency is limited by cost and by precision, not by dose.
Protein target arithmetic
| Body mass | 1.2 g/kg | 1.6 g/kg | 2.0 g/kg | Per meal at 1.6 (÷3) |
|---|
| 62 kg | 74 g | 99 g | 124 g | 33 g |
| 74 kg | 89 g | 118 g | 148 g | 39 g |
| 88 kg | 106 g | 141 g | 176 g | 47 g |
| 103 kg | 124 g | 165 g | 206 g | 55 g |
| 124 kg | 149 g | 198 g | 248 g | 66 g |
At roughly 4 kcal per gram, 141 g of protein is about 564 kcal — a substantial fraction of a 900 kcal budget, which is the real constraint.
The underlying point is that scanning more often than every twelve to sixteen weeks generally produces changes inside the precision error, which reads as noise and gets interpreted as signal.
Between-manufacturer differences in body-composition output on the same subject are documented in cross-calibration studies and are not small.
A body-fat percentage from one machine and one from another are not the same measurement and should never be compared.
Ask the facility for its precision error. If it does not have one, that is information.