Seeing as I was raised in a Christian community, in a semi-Christian home, and it's really a pretty simple concept, I'll adress this first: People of the Christian and Jewish faith (and maybe even Islam? I don't know) believe in the Garden of Eden. From what I understand of it, in this Garden of Eden, nothing harmed anything else. Essentially everything was perfect. What did they eat in the Garden of Eden? Fruit. They had to, to have been living truly in harmony with everything else, and not harming anything else. Therefore, the Christian and Jewish Bible (and perhaps Muslim Qu'ran) seem to illustrate fruit as being the first, natural, purest, and ideal food for..well, everything.
Buddhism, too, seems to advocate a fruitarian diet, perhaps even more clearly than Christianity.
"'Having abandoned the destruction of life, the recluse Gotama abstains from the destruction of life. He has laid aside the rod and the sword, and dwells conscientious, full of kindness, compassionate for the welfare of all living beings.' It is in this way, bhikkhus, that the worldling would speak when speaking in praise of the Tathāgata.
"Or he might say: 'Whereas some honorable recluses and brahmins, while living on food offered by the faithful, continuously cause damage to seed and plant life — to plants propagated from roots, stems, joints, buddings, and seeds — the recluse Gotama abstains from damaging seed and plant life."
These are two small excerpts from the 'Digha Nikkaya,' one of many Buddhist religious readings, which I feel speak for themselves. Enough said.
The last religion I want to touch on is Hinduism, seeing as it is the..3rd (I believe?) most popular religion in the world. Admittedly, I don't know a heck of a lot about this religion. All I do know is that Ghandi, who was pretty much an amazing guy and an exemplatory Hindu, aspired to be fruitarian. He did follow a fruitarian diet for a while, but I have heard that he was somewhat addicted to goat cheese or something, so he had some trouble with that. Nevertheless, his intentions were clear. I suppose perhaps his wish to eat this way had nothing to do with his faith..but I doubt it; I assume he made the decision based on principles that he learned growing up Hindu, meaning that such principals are indeed ingrained in the Hindu faith.
One last thing I want to point out, is that it's not just religion that suggests we ought to be fruit eaters. Most of us believe in evolution. Most of us believe that we evolved from apes, or some sort of monkey like species of the like; I don't know specifics. But I do know that generally, unless I am severly mistaken, animals in this family are frugivores. If we evolved from these frugivores, it is not such a huge leap of faith to realize that - hey. Perhaps we are designed to be frugivores as well.
How many different ways to we need to be told, how clear does it need to be for us before we realize that we aren't supposed to be ripping flesh like wild cats, nibbling grains like birds, or munching herbaceous matter like cows? We are frugivores. We are designed and meant to eat fruit. Forget what the doctor, who won't have a job when you are perfectly healthy, told you. Nevermind that biased experiment funded by the meat and dairy industries, and listen to me; a person who has nothing to gain, but the satisfaction of knowing that I helped a fellow human realize a simple, essential truth: We are frugivores. Eat fruit, be healthy, be happy.☺