Some people tried with all their might, almost to the point of death to live on vegan diets. Some people can do it. Other's don't have the biochemistry for it. Main thing: listen to your body.
http://www.beyondveg.com
Frank Talk about Vegetarian, Vegan, and Raw Diets & Beyond
http://www.beyondveg.com/cat/frank-talk/index.shtml
http://www.chetday.com/billings.html
Beyond Denial: Coming to Grips with Reality in the Veg/Raw Movements
An Interview with Tom Billings
by Tom Billings
Issue 2, February 2000
Copyright (c) 1999, 2000 by Thomas E. Billings.
[Editor's Note: In this interview with Thomas E. (Tom) Billings, a long-time vegetarian with extensive experience in a wide range of raw and living-foods diets, you'll have many assumptions challenged. This piece is not for those whose minds are clamped shut. Tom's involvement in raw, vegan, and vegetarian diets goes all the way back to the late 1960s and early 1970s, when vegetarianism and raw diets were blossoming as part of the counterculture movement of the time. Tom is a site editor for Beyond Vegetarianism,
http://beyondveg.com, a controversial Internet website that challenges many of the traditional beliefs of raw, vegan, and alternative diets. ... -- Chet]