Needs change too. Growing up, there was a family of vegans a few
  blocks away from me. Mother and three kids were all vegan. This
  was back in the early 1980s. There wasn't as much support for
  the extreme vegetarianism as there is now but they did ok. But,
  one day the son who I was friends with, was very unhappy. She
  had some medical scares and the doctor was like, "Lady, eat some
  kind of meat - your diet is killing you here." So, she
  incorporated fish into her diet - the lowest level animal she
  could manage. Her three kids, two teenagers and one kid, all
  remained vegan and she cooked vegan for them, but she had to
  regretfully have fish with her meals but it did the trick. I'm
  sure nowadays there'd be more support though and she'd be able
  to remain vegan.