I'm definately more about tighter controls than about complete abstinance.
I like to have my digestive system fairly vacant, but at the same time ayahuasca is a journey and often a very difficult one. You wouldn't go hiking without a bottle of water and a sandwich in your nap sack would you?
When I was a child I'd pass out on occasion and in more recent years, strong bouts with psychedelics have also brought that on. I surely can't have any worthwhile insight when I'm fighting for my own conciousness. That's actually probably the most counter productive thing in the world. Also there's nothing more confusing then passing out at the peak of a heavy experience with DMT, then coming round... at the peak of a heavy experience of DMT. Yikes.
What I do now is pick something light that is easy to digest and has some good nutrients and nothing fits the bill better than fruits and vegetables. However I try not to eat anything at all for 4 hours before ayahuasca, but I will indulge in some good ol' juice as sugars are very important to me all the way through the experience.
My strictest guideline is if you're purging hard chunks, you've fucked up