Clinical perspective, offered as context rather than as advice. Most of what circulates confidently in this community traces back to one summary of one study, and the qualifier was dropped somewhere in the third retelling.

Dr.AddMedPHL said:

The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the…

Adding the part of the answer the thread has not reached. The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either. Those three things can all be true at once, and most arguments here are two people holding different parts of that.

The figures, for anyone assembling their own picture. Practical: whatever you change, write down the date and the reason. In three months the reason is what you will have forgotten, and the reason is what makes the record worth having.

Following on from Dr.AddMedPHL — and this may be the naive question:

How would you tell the difference between that and the alternative explanation?

Moderator note: a couple of off-topic posts removed.