Former Vegetarian here, not Vegan. I was a vegetarian for 22 years and my understanding is that you can get everything from a vegetarian diet EXCEPT one thing. That is if you eat it in the proper proportions and quantities.
But that one thing is B12, is not found in plant products.
"Some substantial sources of B12 include animal products (shellfish, meat), fortified food products, and dietary supplements." per Wikipedia
You could I guess eat mass quantities of bacteria but then you aren't a Vegan anymore.
I'm not the one to argue vegan(or vegetarian) vs meat, even if I am not vegan. I can see good arguments for both. I just thought this was a fun article, in the way it makes such an "in your face" and aggressive claim for the opposite of vegan when it comes to health. Specifically brain health in this particular article.
"EXCEPT one thing", for sure B12 is one. But what about
K2, A and EPA/DHA? I know you are supposed to be able to get the last 2 by conversion from their plant versions, but it is argued by some(for ex: this article) that process is extremely inefficient and leads to deficiencies. But what about
K2, is there a non-animal source for that? ( although, I think certain fermented vegetables can provide it, like Natto)