I have a niece that saw some movie at school when she was about 10. She became a vegan then. Very stubborn girl (like her crazy azz mamma). I believe her growth was stunted severely by this as she only grew to be 5’ 4” while her parent’s were both 5’ 10” plus. She was always sick and washed out. She was always eating some processed faux meat or cheese product. Never did she eat much raw veggies or cooked legumes. She wouldn’t even eat honey. Finally it got so bad a doctor had to tell her to eat some animal protein because her health was so poor. Soon afterward she became much more healthy and had a baby.
A huge risk of a vegan diet is a deficit in B vitamins. Lack of B3/niacin, especially, will cause pellagra, with potentially deadly consequences.
Well, there's the problem right there. I'm doing just fine with meat being only around 5% of my diet. (It's got to be part of a bigger dish for me to eat it, not a single course of its own, like a steak or burger. I can get at least 10 meals out of a single rotisserie chicken.)