well from what i know from the human evolution we have eat plant and meat and fish. there is a part of us that doctor need to remove sometime called the appendix(vestigial organ) and it seam it is related to us being herbivore in the past and that now we are not able to digest as much vegetable as in the past and that the appendix sometime does not take it at least it is what i have heard many year ago.

We don't really think twice before getting an appendectomy (surgical removal of appendix), simply because the appendix has never really been associated with any particular function. Moreover, removing it does not appear to affect the human body in any manner. Appendix function of assisting in digestion seems to have disappeared in modern humans. Thus, it has been termed as a vestigial organ, which means though this organ may have had a function, it seems to have lost its original role.

In our primitive ancestors, appendix seemed to play a role in digestion. Some scientists believe that primitive man consumed the barks of trees, which is why an additional organ: appendix, was required to digest the extra roughage. However, this is only speculation. There is no scientific proof to validate this point. Moreover, look at all the stuff people across the globe stuff into their mouths. If this were true, these guys would require two to three additional appendices.

http://www.buzzle.com/articles/appendix-function.html

so let say that we have the choice . the proper balence and moderation is the key. i eat what i feel like eating. i think that the body know best. the flesh crave what it needs. will also add if we would not be made to have dairy product why do female produce milk? we also know that milk is good for the bone but to much milk cause asthema. meat and nuts and noodles contain protein and is good for cells regeneration it help you build muscle. also fruit and vegetable have many good and bad effect. fish is also good and procure omega3 to the body, so the key is balence and moderation. i do not think it is wise to divide to just one category, doing that would probably create imbalence in your system. also diet is not good because after you eat twice as much i would say go take a walk or do sport or activity then you will be in better healt. this is my humble opinion.

Christ said that what comes out of your mouth is more important than what goes into it.. Matthew 15:11

I know for me my diet hasn't changed over the years. I know it says in many spiritual articles be a vegan only eat things that are not living. It even said in Astara this but for me I haven't changed my diet and I feel pretty connected to God.

I think it is a personal choice and as well a personal choice to feel better or more spiritually awakened because of the choice to not eat meat, fish or birds.

It may be better for our systems, but I am not sure on that since our teeth are designed to rip apart meat, we are designed to be carnivores.

diet is one of several changes that has occurred, as well as preparing what i eat.
had i the knowledge of the plant kingdom and how to produce 'prana'
it may not be necessary to consume as much to stay alive and healthy.
less meat is now taken as taste is not a primary concern,
but the ecological and other consequences of raising for slaughter are.