The Messianic Jews say the Old Testament food laws were never repealed. I also heard on the Bema podcast that part of Mark 7:19 ("Thus Jesus declared all foods clean") shouldn't be in the Bible—that it was added to the original text.
This is simply not true. The words in question appear in the best ancient manuscripts. Let's examine the text.
Jesus says, "There is nothing outside a person that by going into him can defile him, but the things that come out of a person are what defile him.” ... And he said to them, "... Do you not see that whatever goes into a person from outside cannot defile him, since it enters not his heart but his stomach, and is expelled?” Thus he declared all foods clean (Mark 7:15, 18-19).
Besides, what about passages like 1 Tim 4:3-4 and Heb 13:9? They do not support the kosher interpretation. Certainly we benefit from knowing the Jewish background of the New Testament, the apostles, and Jesus himself. However, kosher laws are no longer part of the covenant. (For more, please refer to the series on Messianic Judaism.)