Kill and eat.

~Acts 10.9-16 About noon the following day . . . Peter went up on the roof to pray. He became hungry and wanted something to eat, and while the meal was being prepared, he fell into a trance. He saw heaven opened and something like a large sheet being let down to earth by its four corners. It contained all kinds of four-footed animals, as well as reptiles and birds. Then a voice told him, “Get up, Peter. Kill and eat.”
“Surely not, Lord!” Peter replied. “I have never eaten anything impure or unclean.”
The voice spoke to him a second time, “Do not call anything impure that God has made clean.”
This happened three times, and immediately the sheet was taken back to heaven.

~Acts 11.1-18 This story is repeated as Peter tells it to the leaders.

Kill and eat. It's a heavenly mandate. From the story we clearly see that the message to Peter is not just about food; however, again a food analogy is used. I conclude that, at least since the fall of mankind into sin, God is ok with killing animals and using them for food. The Bible in no way recommends a vegetarian diet.

Furthermore, I think we can deduce here that since it says "all kinds of four-footed animals" this would include even pork. Peter is not comfortable with the idea. In fact, it's so radical, so contrary to all that the law of Moses has taught, that God shows him the same vision three times to be sure he gets it.

Perhaps Peter remembered Jesus saying it's not what goes into the mouth that makes someone unclean, but what comes out (Mark 7).