In regards to eating meat

[Tenet Nosce]

Carnivores cannot survive on cellulose. They may on occasion eat grass, but they use it medicinally, usually as a purgative to clear their digestive tracts of parasites. Ruminants, on the other hand, have evolved to eat grass. They have a rumen (hence, ruminant), the first in a series of multiple stomachs that acts as a fermentative vat. What’s actually happening inside a cow or a wildebeest is that bacteria eat the grass, and the animals eat the bacteria.

Lions and hyenas and humans don’t have a ruminant’s digestive system. Literally from our teeth to our rectums we are designed for meat. We have no mechanism to digest cellulose.

This statement is not entirely correct. Humans, also, have bacteria that live symbiotically in their digestive tract which can digest cellulose, and other forms of fiber. I wouldn't characterize humans as carnivores, but omnivores. The rest of the argument appears sound, according to my own biased opinion.

This following thought falls under the "pure speculation" category... but we do know that the human body is associated with three distinct gut enterotypes. I wonder: what if one of them required grains, and one of them required meat, and one of them neither. Other possibilities than these three, of course, could exist.