I think it can be very harmful to growth and development. I know a vegan family, the father is 6'3", the mother 5'9". By all rights the kids should be tall but the tallest is only 5'9" and the shortest 5'7", they're 24, 22 and two are 19 (twins), all male and scrawny - I think they've seriously been screwed over by their parents chosen diet, I would be seriously pissed off if I were them.