Yeah, I think to adequately test the coffee hypothesis, you’d have to quit coffee for a while, eat the exact same diet (which means eating at the same times) for say 1 week, get tested, drink coffee while eating the same exact diet, for 1 week, get tested. Also, don’t change exercise either. Compare results. If you wait at all or change your diet or eat at different times, you might change the results.
And this is probably like everything else, some people’s values will change more than other people’s values will.