> We just don't know, and anyone that tells you they do know is either selling you something or, at best, telling you what worked for them.

I read a great newspaper article ten or so years ago. The journalist visited a vegan and a person following LCHF (low carb high fat). Both said that their diet made them feel great, made them lose weight, gave them lots of energy, kept them free of illness, and so on.

The journalist noted that they basically split the nutrition circle (I don't know if this is a world-wide thing, but it divides different food sources into pie slices) in half: the vegan eating the grain and vegetable parts and the LCHF person eating the animal parts.

The article basically showed how good the human body is at making up for when you limit an omnivore diet. If you asked any of the two participants, they would say their parts of the nutrition circle were the healthy ones.