In the last few years I've incorporated intermittent fasting and longer, extended fasts into my lifestyle. Extended fasts are part of all ancient cultures and religious practices, and for good reason.
This video provides a good overview of what happens in your body as you do an extended fast. A little wonky at times, but easy to follow. FWIW, I ate yesterday morning at 10:00AM and will not eat again until Friday. (I am posting this on Tuesday morning.)
I hope you find it useful.
That might work for those that have 'extra reserves' but some, as I, don't have those reserves. That said there is such a thing as intermittent fast. I always go at least 12 hours from the end of my last meal to the start of my first. Also, almost never any snacks and if so it is usually a piece of fruit.