I was gunna mention marmite/vegemite as a B12 source, but chubby boy beat me to it.

I always laugh when people who eat fish and chicken call themselves vegetarians. I can't remember the last time I went out to my vege garden and pulled a fresh chicken or snapper out for dinner

Adequate protein intake is a real problem for vegos and particularly for vegans. You can get some from dairy and a reasonable amount from eggs, but you really have to get most of it from eating lentils or other plants containing protein - anyone for brussel sprouts? Active people who can benefit from a bit more protein can struggle to get enough from those sources.

I have a mate who became vegetarian back in the 80s when he became a devotee of Sathya Sai (a fuzzy haired Indian guru) but had to fall off the wagon a few years ago when he was mid-way through a season of an amateur opera production he was in because he was running out of gas working and singing every day.