That is what we’ve been lead to believe, but it seems we don’t. If you stop feeding your body carbs, your body naturally transitions to using fat instead as an energy source.
From my understanding, our ancestors thrived on eating meat they hunted and only deferred to other sources (e.g….berries) if needed. Depending on what part of the world they lived, meat would have been the only food source during much of the year given the weather. (The Inuit people (i.e…Eskimos) of northern Canada still eat this way.) They’d most likely have gorged themselves upon a successful hunt, and then not needed to eat for days after. I believe this is why people are finding benefits today with intermittent fasting…by necessity, we evolved over thousands of years with our bodies not expecting to be feed as often as we do today.
I get the premise and personally I've focused on at least not eating much for a couple of days after a 'big' day....but wasn't the life expectancy back then like 13 years too?