Sometimes the devotees of Lord Krishna are asked why they abstain from eating meat, and sometimes from another side they are asked why they take milk products. His Divine Grace Srila A.C Bhaktivedanta Swami Prabhupada elaborates on the actual nature and reason for the Hare Krishna diet in the following conversation excerpt.
Mr. Dixon: The stricture on the eating of meat, does that derive from the fact that animals have their lives which are accorded...
Prabhupada: No, vegetable, vegetable has got life.
Mr. Dixon: Yes. What I'm asking is that because animals have a higher priority in life than vegetables?
Prabhupada: No question of priority. Our philosophy is that we are servant of God. So God will eat, and whatever remnants of foodstuff He'll left, that we shall take. So in the Bhagavad-gita... You find out this verse. Patram puspam phalam toyam yo me bhaktya prayacchati (BG 9.26). Just like you have come here. So if I want to offer you something for eatable, it is my duty to ask you, "Mr. Nixon, which foodstuff you'll like to eat?" So you dictate, "I like this very much." Then, if I offer you that foodstuff, then you become pleased. So we have called Krsna in this temple, so we are waiting, what foodstuff He wants to eat? So He said that...
Guru-krpa: "If one offer me with love and devotion a leaf, a flower, fruit or water, I will accept it."
Prabhupada: Yes. Patram puspam phalam. He is asking very simple thing which everyone can offer. Just like a little leaf, patram, a little flower, puspam, a little fruit, and little liquid, either water or ghee, er, milk. So we offer that. We make different varieties with these ingredients, patram puspam phalam toyam (BG 9.26), and after Krsna's eating, we take it. We are servant; we take the remnants of foodstuff left by Krsna. We are neither vegetarian nor nonvegetarian. We are prasad-ian. We don't care for vegetable or not vegetable, because either you kill a cow or kill a vegetable, the sinful action is there. And according to nature's law, it is said that "The animals which has no hand, that is the food for the animals with hands." We are also animals with hands. We human being, we are also animal with hands, and they are animals—no hand but four legs. And there are animals which has no leg, that is vegetable. Apadani catus-padam (SB 1.3.47). These animals which has no leg, they are food for the animals with four leg. Just like cow eats grass, the goat eats grass. So eating vegetable, there is no credit. Then the goats and the cows are more credit, have more credit, because they don't touch anything except vegetable. So we are not preaching to become goats and cows. No. We are preaching that you become servant of Krsna. So whatever Krsna eats, we eat. If Krsna says that "Give me meat, give me eggs," so we shall offer Krsna meat and eggs and we shall take it. So don't think that we are after vegetarian, nonvegetarian. No. That is not our philosophy. Because either you take vegetable or you take meat, you are killing. And you have to kill because otherwise you cannot live. That is nature's way.
Mr. Dixon: Yes.
Prabhupada: So we are not for that way.
Mr. Dixon: Well, why do you put the stricture on...
Prabhupada: Stricture in this way, no meat-eating, because cow protection is required. We require milk. And instead of taking milk, if we eat the cows, then where is milk?
Mr. Dixon: So milk is very important.
Prabhupada: Very, very important.
Mr. Dixon: In terms of production of food for the world, the world would be much better off without eating animals.
Prabhupada: No, milk is required. Some fatty vitaminous food is required. That necessity is supplied by milk. Therefore specifically...
Mr. Dixon: Couldn't you get all the necessity you require from grains?
Prabhupada: Grains, no. Grains, they are starch. According to medical science, we require four different groups: starch, carbohydrate, protein, and fat. That is full food. So you can get all these things by eating rice, dahl, mean pulses, and wheat, and.... These things contain.... Pulses and wheat contains protein. And milk also contains protein. So protein we require. Fat we get from milk. Fat is required. And vegetables, carbohydrate; and food grain, starch. So if you prepare nice foodstuff with all these ingredients, you get full..., and offer to Krsna, then it's purified. Then you are free from all sinful activities. Otherwise, even if you kill vegetable, you are sinful because it has got life. You have no right to kill another life. But you have to live on life. This is your position. Therefore the solution is that you take prasadam. If there is sin by eating vegetable or meat it goes to the eater. We take the remnants, that's all.