SoftwareMaven, I will suggest that one possible explanation is that our gut is filled with microbes (some good, some bad) and food is filled with microbes and, by weight, our poop is 50% microbes of some sort. So when you fast, you clean out bugs from your system, some of which are very not good for you. We seem to have lost this idea that we are organic, living creatures, part of a complex biome and seem to have this fantasy that we are merely ...chemically complex and in need of more building blocks. And life is just way, way more complicated than that. It is much closer to an on-going, multi-front battle. And when you never fast, you never take a break from that battle. It just keeps on going.

my 2 cents, fwiw.