This might seem like a dumb question, but if if you have water retention and you get a fat test using calipers, would you appear leaner than you really were than if you were not holding water?? Or would that matter at all?
Actually water retention would increase skin-fold thickness, therefore artificially increasing your bodyfat percentage (making you appear fatter than you actually are).
Would the same apply for a bioimpedance scale?
I would think that it would probably alter the results as well, especially in the scales that you stand on, as they do not give an estimate of total body water. BIA machines use the reactance and capacitance measurements to base its calc. Some machines actually base these measurements on measurements on DEXA scans and give you an estimate of intra and extracellular water as well as fat. RJL systems makes one that does this. I’m not sold on the accuracy of BIA as the ones that I have used have overestimated my BF. I have done numerous underwater weighings and skin-folds during my undergrad days in Exer. Phys program and I was always about 8%. When using the BIA it would be 15% (they do state a 5% sd of error). I had a visible 5-6 pack at the time so I know the reading was high. The most important thing is not necessarily the accuracy, but the reproducibility. Even if it overestimates you, if it does it the same every time, then it can be used to track progress.
Typically they tell you not to do the BIA close to the time you have been exercising, or sitting in a sauna, etc.