The first piece of dietary advice for the Israelite priests appeared in Leviticus in relation to how the priests managed the various offerings:
Leviticus 3:17 You must never eat any fat or blood. This is a permanent law for you, and it must be observed from generation to generation, wherever you live.
It was said in the context of the sacrifices for the various peace, sin, guilt and other offerings, and it was repeated in Leviticus 7 in that same context. And there was no getting around it by raiding carcasses.
So don’t go taking something that belongs to God: in this case it was the blood and fat from livestock, especially sacrifices.