Citation for proof that arterial hardening happens immediately, and that animal protein specifically causes this (vs plant protein)? I've not seen this specific claim before.
It seems to be part of some pseudo-vegan zeitgeist. The denaturation process in cooking and digestion makes animal protein practically indistinguishable from plant protein. If there is any measurable dietary effect, it would be in the nutritional factors closely associated with those protein sources--for instance, the heme iron in animal meats, and the porphyric magnesium in green vegetable chlorophyll.
The proteins themselves are unlikely to have an effect beyond the ratios of their specific amino acid components, and the potential for indigestible misfolded prions. Animals are loaded with pepsins in their guts and proteases in the rest. By the time an amino acid reaches your arteries, if has already been broken down and built back up into something else.
A simple web search turns up pseudoscience and broscience everywhere. If there ever was a real dietary health study, it's now buried in the noise.
