definitely some good points on the fasting, isolation, ect... very basic fundamental concepts of purification are being played out here... they are good points.

but i think its important that people understand that these methods are not necessary AT ALL! it may be for people participating in a living in the amazonian jungle but they arent really necessary for people out side of that... some disagree with me and that is fine and a matter of opinion as well... but an educated one at that...
for example...
one doesn't need to fast with ayahuasca and eating very little of specific foods does create an heightened sensitivity and purification but its not necessary either...
the foods that are choosen as taboo ( please see a full list of amazonian ayahuasca dieta taboo foods in eduardo lunas book vegetalismo) are many... there are specific types of bird and monkey that are ok and others that are not... same with plants and fish... its not all beans and rice and plantains... boar is ok to eat but domestic pig is not... ect... so the foods eaten on a deita has more to do with food taboo then any thing honestly... but yes it allows a socially sanctioned purification system still based on psychosomatic dynamics to occur.
back to fasting how ever... you dont need to fast... an arguement that drinking on an empty stomache is fine... have a day of eating light as you normally do... and then waiting about four hours before one drinks is a good strategy... you have energy... your not in a weakened state... these weakened states induced by isolation and fasting can be great for creating transpersonal ego dissolving states, which are terrifying and great for disassembling things... but they can also be extremly confusing and difficult to assimilate as well as intigrate into your life...
now having some strength in you from just a normal diet and eating that day and THEN eating a small amount of food right after drinking can induce POWERFUL POWERFUL visions. eating food after drinking ayahuasca can take a tea session where no visions would have ever occured and turn it into a POWERFUL visionary experience with many lessons learned and healing produced...

SWIMS experiences with eating food and not fasting as apposed to the dieta experiences with traditional ayahuasceros have huge differences...
the experiences of not fasting and eating food during a session ( often times sour dough bread cuz its yummy and good for you) bring about greater focus, greater healing, greater ability to take care of your own needs then having a shaman there to do it for you because your in a weakened state... more was accomplished more was learned, and the healing that occured was longer lasting and more effective in the long run in changing swims life then in the experiences with the dieta and not eating during the session.
SWIM would eat light after drinking and would not eat anything to heavy... but fatty foods can really kick it in too...

if you look at the pros and cons... swim was able to have full on transpersonal ego disolving experiences where tremendous healing and learning occurred with out freaking the fuck out and loosing his shit and having some all powerful healer take care of swim... swim felt more empowered and capable of taking care of his own spiritual quest and needs, as well as physical needs. the qualitative effects as well as the experience over all made more sense to swim because swim was not trying to entertain notions from a foreign culture as well... one that swim does not belong to nor will ever fully belong to even if swim felt adopted or reborn into the cultural group swim was working with...

SWIM has notions that the fasting, and isolation and food taboos of the dieta may actually just be there to reinforce social hierarchy among shamans by breaking down a student of the plants ego just enough and then appearing as the guide in the students process...
if one did not participate in these practices my hypothesis would be that one would feel more empowered to take on ones own healing path cultivating a more egalitarian relational dynamic with the plants as the teachers first and for most...
the plants them selves already do a hell of a job of dismantlement egoic constructs and reforming them in healthier patterns... if this can be done in a fully conscious co-creative way with human consciousness working in synergy with the plant then i believe more benefit would occur.
when we participate in a cultures spiritual practices we also participate in their social practices, they are intertwined... amazonian traditions tend to be hierarchical, patriarchal, sexist and at times conflict driven and competitive... these are social and cultural adaptations that have allowed them to thrive... and theirs nothing wrong with that in my book... nothing wrong with that for them... but not for me personally... thats not what I am interested in nor desire to incorporate into MY life... and I question as to whether many people wish for that as well..
like i said though this is just my loose hypothosis on the cultural and social aspects of amazonian healing practices... people can disagree with me as much as they like... i personally dont care...

but ive seen enough and seen the differences that establishing your own relationships can make... i personally do not see a real good reason why a bunch of gringos HAVE to do the dieta...
they can if they want to... have fun with that...
but its not necessary...
the plant spirits will come to you and teach you and work in synergy with you whether you do it others way or your own... but i guarantee if its your own way that you learned your SELF from you OWN interactions the experiences are going to be easier to integrate into your life and more effective in seeing positive change occur in your day to day life... changes that others will see...