(Yes, I already posted about my sister who's gone vegetarian as a first step towards veganism, thanks everyone for your suggestion, she's getting her hunger and bloating issues under control now...)
My brother really believes in animal rights and is hugely against factory farming, but he's in a dilemma, because he's recovering from cult starvation and is underweight for his height and has been for some time. At 6' he only weighs 143 lbs. (Yes, we know there are some very slim/wiry vegans out there, but for his frame and build, this is an unnatural weight. Other men in the family who are similar height/build, slim, eat healthy, and are very active weigh at least 180 lbs.)
He needs to gain muscle to be at a healthy physique, and so he's been holding off on going vegan because he believes he needs the meat and dairy to help him gain weight, and he's afraid if he goes vegan he'll lose weight or not gain or at least have a very difficult time gaining.
What's everyone's thoughts on this? Can he gain muscle at a good rate without having to rely on meat and dairy? He really wants to transition but he's afraid to at this point due to the weight issue.

