None of that is actually true.
I wont go into the deep details of it all, because minds are already made up, but Ill briefly address the 4 most common egregious errors made by vehement supporters of the human-true-omnivore argument, simply for the record.
And just to clarify, true omnivores are very similar to true carnivores. They are usually interchangeable in the context of comparing humans to either of them. So that should be kept in mind.
1: Protein developed the brain and fuels it: Incorrect.
The brain is fuelled by glucose, and in the absence of glucose, ketones. Glucose does not come from meat directly (read below). It comes from easy conversion of simple and complex carbohydrates; mostly simple, but neither of which are in meat in any appreciable quantities.
The early human brain was almost certainly “fuelled” by, if we are to ascribe a specific food source as responsible for its growth, cooked starches. A cooked potato is 20x more digestible than a raw one, and is utterly packed with carbohydrates, which very easily convert into glucose. The only “evidence” of meat creating brain growth in humans is the very loose correlation of animal bones found at old camp sites. The conclusion jumped to that those bones meant heavy meat consumption is just that, a jumped too conclusion that has yet to be proven, but is still clung to as fact anyway because it supports a theory and life style that simply does not hold up to scrutiny and glaring questions, such as if meat fuels brain growth, why are true omnivores/carnivores not hyper intelligent super beings who have in some cases such as the crocodile, been eating meat that supposedly grows brains, for 200,000,000 years, about 1000 times longer than the “modern” human? What about lions? Wolves? Bears? Etc? Where are their gigantic leaps in brain size due to meat consumption? What is the unique human mechanism that accounts for complex proteins growing something that it is neither fuelled by, nor composed of in any way (the brain is 0% muscle tissue)?
Do humans need essential amino acids (the simplest proteins not able to be synthesized by the body) for brain development? Most certainly; but there is no essential amino acid that is restricted to occurring in flesh, and lets be honest, when someone mentions “protein” in this context, they are not talking about essential amino acids (all of which can easily be found in fruits and vegetables), they are talking about animal muscle tissues.
One thing is correct here, though asserted for the wrong reasons: it takes a lot of protein to fuel the brain, true, but thats because of the great inefficiency the human body has in processing complex proteins (flesh) into something actually usable. Complex proteins go through many stages of break down (all consuming large quantities of energy in the process) before actually turning into something useful, and since there are no appreciable carbohydrates in meat, there is no immediately usable material by the brain (or body).
The exact break down I cannot list, but after many stages of break down, youll eventually convert unused calories from the meat into fat, and fat can be processed into glucose in an inefficient way via something called beta-oxidation if I remember correctly, to produce emergency supplies of glucose to the brain to keep it functioning at a sub-standard level and supplement the ketones (already back up energy; its in principle the difference in energy density between wood (ketones) and diesel (glucose)) that are made by the breakdown of complex proteins and fat.
2: Humans evolved to eat meat: the entirety of our physiologies suggest otherwise.
There are literally hundreds of valid physiological contrasts between humans as behavioral omnivores and true omnivores, but there are some that truly stand out, such as the differences in GI tracts, stomach acidity, dental structures, salival enzymes, taste receptors, nails vs claws, colon structure, jaw movement (lateral movement), vitamin C synthesis, and others.
And its very apt to mention long term studies of the health of primarily meat eating societies (Inuit) vs non-meat eating societies (numerous). Inuits average -10 years of life expectancy, versus up to +10 for non-meat eating groups.
3: “But canine teeth!”
Horses and sheep have canine teeth too. Small ones (kinda like humans!), but canines nonetheless. And a gorillas canine teeth could pierce your skull; does that make any of them omnivores? Thus the canine tooth argument is laid to rest.
4: B12 is essential and is only found in meat products. False.
The B12 argument is the least unsound out of a broad spectrum of very unsound arguments, but is still fundamentally flawed in its reasoning.
No mammal naturally produces B12. In fact, no animal at all produces B12. Neither does any known plant, nor any known fungus. This means that farm animals used for meat are not a primary source of B12, thus the claim that B12 “only comes from meat” is impossible.
The only known sources of B12 are prokaryotes (basically bacteria). Many animals have bacteria in their guts that produce B12 including humans, but its not absorbable due it being produced in the colon. In some animals it is, including some ruminant farm animals, assuming they get enough cobalt in their diet, however if they do not, they get it elsewhere from natural sources, such as dirt and untreated water.
Dirt and untreated water. Two things humans up until very, very, VERY recently, have been intimately familiar with.
Early man was practically swimming in filth, and thus, had ample supplies of B12. So the B12 argument at its core, being one of “if you dont eat meat youll die because of B12 deficiency, thus humans have always eaten meat to get B12, thus it is natural” is easily debunked.
5: Im going to add a fifth argument that is not usually directly claimed, but is often indirectly claimed: it is human instinctual nature to eat meat like any other omnivore: easily proven false.
Put a kitten into a room with a mouse and a banana. Which does it see as food, and which does it see as inedible/a toy?
Put a human baby into a room with a bunny and a banana. Now ask the same question.
There ya go.
Acquired societal behavior =/= nature and instinct.
Ok, I guess thats it about that. I wont change anyones mind, and thats fine, but I had to address some points on this topic.