Some things are right because God commands them, other things God commands because they are right. The first category is provisional and changeable, the second--definitively fixed. The fixed category is what we would call moral or natural law; people will instinctively know it's right. Thankfully, food is not moral law.
Long before the giving of the law to Israel, God laid down specific dietary instructions to Noah, and through him, all the future inhabitants of the world; it was to be a global menu. Likewise, the dietary instructions were very broad: “Every moving thing that is alive shall be food for you; I give all to you, as I gave the green plant. Only you shall not eat flesh with its life, that is, its blood." -Genesis 9:3-4 (NASB)
Many generations after Noah, God singled out a people and gave them new dietary instructions, specifically to distinguish them from all the other peoples of the world. These new regulations would also provide a daily test of obedience to God. The new Jew menu was very restrictive and race-specific; thus the often repeated phrase in the dietary instructions of Leviticus chapter 11, "it is unclean to you".
A moral implication of the dietary laws was that since God specifically commanded them to Israel, it would be wrong for them to disobey; the dietary laws were right only because God commanded them. But then again, God could change the rules anytime He saw fit, and this He did, as Peter found out in his famous vision recounted in Acts 10.
With the coming of Christ, the Lord reverted back to the broad dietary instructions of Noah, because the gospel of Christ, like the Ark, was going global. The dietary law's differentiating purpose would no longer be in play, since Christ--the new Differentiator--took their place. "For everything created by God is good, and nothing is to be rejected if it is received with gratitude; for it is sanctified by means of the word of God and prayer." -1 Timothy 4:4-5 (NASB) Think of this the next time you bite into a pork chop.
God is great. God is good. Let us thank Him for our phood.