Human = Animal.
Just like all other animals we are built to be sleeping running fighting f****** or eating. And the lattermost activity is after differently durationed periods of some mix of the former activities. I still haven't figured how we devolved, yes devolved, into cubicle desk-dwellings...
Delusions of grandeur of this reasoning thing in humans is what derails most people. Periods with zero caloric intake are absolutely 100% natural. Even hippo's go long periods without eating, and there's one big perpetually fat nasty thing I would never want to tangle with and for which I have tons, haha, of respect.
My "modified" IF, since learning more and more around these boards, is a now perpetual background meditation process of listening to what my body reports that it needs combined with what I know it needs. Sometimes I have three eggs in the morning sometimes I do not, sometimes I nibble on a few nuts during the day sometimes I do not(I really really want to be precisely as strong as a squirrel some day, those little bastages are quite impressive), always maintain water intake and eat whenever I get around to eating in the evening. Natural "Hunting and Gathering"... I've never been stronger, and body composition of late is changing rapidly since pushing into the even less food levels area from the time period between bedtime to the next days kill er I mean dinner.
I see nothing but continually increasing productivity as I refine food sources and body-listening more and more.