JenPlateau said:

The useful move here is to separate what is established from what is widely repeated.

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.

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

One concrete data point for the thread. 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 same conditions. Nobody wants that answer and it is still the answer.

One thing that is still open after JenPlateau’s answer:

How long did you give it before you decided it was working?

jason_paloalto 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…

Pushing back on jason_paloalto here. This treats a plausible mechanism as a demonstrated one. Plausible is where you start looking, not where you stop.

jason_paloalto 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…

No disagreement, though the timescale matters more than the mechanism here. Most of what looks like a difference in kind turns out to be a difference in how long somebody waited.

If somebody has the primary source to hand I would rather cite it than paraphrase it.