I've been a vegetarian since 1996, although my husband and I have periodically added to the foods we eat. Except for a multivitamin, I've never taken supplements of any kind. I was anemic for a while and had to have IV iron infusions, but I haven't had any problems for the past few years.
Initially, we were vegans; then we added in nonfat dairy (since I don't appear to be lactose intolerant) and Eggbeaters; and eventually, after several years, we added seafood. But I haven't had red meat or poultry of any kind in 12 years. The only times my diet got difficult involved the four months when my (incompetent) GI doctor thought I also had celiac disease--and the 3 years that I was on a low-fiber/low-residue diet (when I pretty much ate just starches and dairy and fish, and my whole diet went to hell). Otherwise, I function fine--although I have to avoid all the fruit-and-veg things that give Crohn's people problems (like peels and husks and seeds).