Yep. I only drink black coffee, no sugar, and I don't eat sweets, cookies, or anything. In fact, I mostly don't consume anything but coffee from I wake up until dinner time, 6-7 PM.
Haven't noticed any of the supposed side-effects doing so could cause. For a while, not eating for hours was also supposedly bad for you. Then fasting started to show benefits. It turns out traditional dietary advice might not be worth jack shit.
One study found a slight increase in acid reflux when drank on an empty stomach, a problem I don't have, other than that there does not seem to be any associations with gastritis, ulcers, or dyspepsia.
Yes, intermittent fasting is said to be quite good for organisms. Maybe a form of hormesis. I'm unfortunately not in a position to comment much on caffeine's health effects aside from various interesting and likely true points of speculation but I find what you shared interesting and do not doubt for a second that medical science (including nutrition, and immunity) is not properly understood except by a rare handful who have the ability to see things whole.
I believe coffee has a lot of beneficial properties, but I have a slight concern regarding caffeine as it reduces CBF. That might impair cognitive functions. Supposedly you can mitigate some of the vasoconstriction with flavonoids.