Well...it is really God's diet not the Old Testament diet. For example in 1 Peter 1:16 Peter says ..for it is written Be holy, because I am Holy. Peter here was quoting from Leviticus 11:44. This is the chapter of the Bible where God tells His people what food should be eaten and not eaten.

Anther example - Acts 10 has nothing to do with food and does not show God saying you can eat whatever you want. Peter interprets his dream and what it really meant. Acts 10:28 "Then he said to them, “You know how unlawful it is for a Jewish man to keep company with or go to one of another nation. But God has shown me that I should not call any man common or unclean."

Another example Hebrews 13:8 "Jesus Christ is the same yesterday, today, and forever." If you believe that and believe the God and Jesus are one, John 10:30 "I and My Father are one.” then God/Jesus didn't change and His instructions are still valid even today. Can we still do everything, no, but that doesn't mean we don't keep the ones we can keep.

Another example.... The stoning of Stephen, what were the charges against him? Acts 6:13-14 "They also set up false witnesses who said, “This man does not cease to speak blasphemous words against this holy place and the law; 14 for we have heard him say that this Jesus of Nazareth will destroy this place and change the customs which Moses delivered to us.” The accusation against Stephen and Jesus were made up and were false, meaning Jesus didn't come to change the law or anything that Moses delivered or wrote down.

Another example...
Matthew 5:17-19 “Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill. 18 For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled. 19 Whoever therefore breaks one of the least of these commandments, and teaches men so, shall be called least in the kingdom of heaven; but whoever does and teaches them, he shall be called great in the kingdom of heaven."

Jesus says that until heaven and earth pass away nothing from the law will pass away. We don't get the new heavens and new earth until near the end of the book of Revelation, meaning what He said in verse 19 is happening even today.

Ok, I promise....last couple of verses! :-)
John 4:24 "God is Spirit, and those who worship Him must worship in spirit and truth.”
John 17:17 "Sanctify them by Your truth. Your word is truth."
1 John 3:4 "Whoever commits sin also commits lawlessness, and sin is lawlessness."
Matthew 7:23 "And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!’"

1 John 2:6 "Whoever claims to live in him must live as Jesus did."

Thanks for reading my long response Sir Janton!
I pray that God blesses you and your family!