Quoting a lot of studies makes a great impression, but it's only worth it if you're not cherry-picking. Have you read the actual studies he's quoting? I did. Well, I read the first 50 or so. More times than not, they did not give what he says or he is interpreting the result so it matches what he likes them to say. Many are done badly. Many studies are done by hardcore vegans or animal right activists. He quotes the same studies multiple times, adding another references each time he quotes it again (making a great impression!).

A vegetarian diet may be the healthiest there is - I don't know. But Greger is biased for sure.