The answer
The New Testament directs us to think of uncleanness in a spiritual not a literal way. It is no longer a list of clean or unclean food. However, if I know that a certain kind of food is harmful to my body and still eat it, then I commit a sin. In addition, even if this food is not harmful to my body, but I know that it will make my brother stumble, then I should not eat it otherwise I am committing a sin.To eat anything that harms the body is definitely a sin because the Holy Bible says, "Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own?" (1 Cor 6:19).
You mentioned "everything is permissible for me" (1 Cor 6:12) but you didn't continue the same verse which says "but all things are not helpful" (1 Cor 6:12). So although I can eat any unclean food, it is not helpful to do so. God is giving us the free will to choose to keep our holiness or to defile ourselves.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)