I became a vegetarian at the age of 12 for ethical reasons.  Some 22 years
later, I started exploring different things.  I tried fruitarian for a
month.  I was vegan for a while.  Then I tried raw vegetarian for a while.
Eventually, I stumbled across Instinctive nutrition via the raw community
online.  I tried that for about a month and loved it.  I began eating raw
oysters and sushi and felt great.  I decided it was kind of expensive
though.  Instincto was followed by paleo and the Zone.  I felt fantastic
on the Zone diet.  Heightened awareness, clear thinking, etc.  I did
notice a drop in high output stamina though.  I also noticed an
improvement in short term memory and my ability to drive long distances
without falling asleep.  It had gotten to the point that I couldn't
remember a phone number long enough to dial it, nor drive an hour and stay
awake.  I don't know what caused these problems, but the switch from
vegetarian diet markedly changed them.

Maybe I ran out of B12?  Who knows?

I know that eating a more natural (paleo) diet is more environmentally
expensive.  I suspect the planet can't support the current human
population eating paleo.  I still remember the day when I was a kid and
watched my father and grandfather butcher a sow.  I remember wondering how
we'd like it if aliens decided we'd make good livestock.

At this time, I choose paleo-zone for me.