I was a vegetarian for about five years. I tried being a vegan for about four months, and my cycles actually got messed up, and since I had always run that train on time, I went back to cheese and eggs.
I stopped being a vegetarian on a long-distance hike in 1999 when I decided some tuna sounded good. I ate fish (mostly sushi) for about a year, and then finally just went back to eating meat.
I gained a ton of weight during my vegetarian years. The diet just did not agree with me at all.