Dr.PathRoch said:

One practical note: write down what you did and when, before you need it.

Correct, and worth adding that it is reversible. Nothing being described here is a one-way door, which changes how cautious it is reasonable to be.

Ask again with the specifics and you will get a better answer than this one.

Dr.PathRoch said:

One practical note: write down what you did and when, before you need it.

That reframing is the part I needed.

Adding the clinical framing, because it changes how the question reads. There is a difference between no evidence and evidence of no effect, and this subject is one where the two get swapped freely in both directions.

Reporting back.

Closing this out. What actually changed my mind was the point about waiting for a trend instead of reading a single measurement, which is embarrassing in hindsight and worth saying anyway.

Dr.MetabolicMD said:

There is a difference between no evidence and evidence of no effect, and this subject is one where the two get swapped freely in both directions.

There is a second half to this that has not been said yet. 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.