Human teeth are those of omnivores. Hard to dispute we were not meant to at least eat some meat.
As for vital elements lacking from a vegetarian diet, I'd say amino acids would be of the most concern as far as need for replacement.
Finally, frog legs DO taste like chicken, albeit a bit sweeter. At least to me, and I've gigged them for most of my life. It's just like there are 7 flavors of meat in a snapping turtle.