Your last question is addressed by Tom in this fabulous conversation with Evita Ochel on Youtube:
That's a disastrous
conversation in which Tom espouses his vegan beliefs. Not only he confuses essential nutrients that must be obtained through diet like vitamin B12 with stuff that the body produces itself like adrenaline and insulin saying that if it produces those 2, then it can produce B12 as well. He also claims that animal protein and animal foods in general are substandard nutrition, when in fact all the evidence points to the opposite. He also says that cows and steers are big, muscular animals and they got like that just from eating grass, so we humans don't need meat for protein to build muscle. Using that absurd logic, there's plenty oxygen in the ocean, fish use it, why don't humans live underwater then? :)) If you look at Tom in 2008 (https://www.gaia.com/video/path-afterli ... er=preview
go to min 2:01) before he went vegan and then 10 years later (https://www.youtube.com/watch?v=i5_yGxALSRY
go the second half, where he's in a t-shirt), you'll notice that despite having an exercise routine, he gained quite a bit of a belly and appears more gaunt in the face.
This leads to a question: how can Tom on one hand come up with a brilliant theory like MBT and on another hand justify veganism with logic such as: steer eat grass, steer are muscular, therefore humans can pretty much do the same. It's like the logic of Einstein and that of a 7-years old in the same person.