Mark was extremely descriptive here just as Matthew, chapter 15:17, explained this problem about unclean food. Mark indicated that Jesus seemed a little upset that they still did not understand what he was telling them about defilement. Jesus said that any food did not enter the heart (ὅτι οὐκ εἰσπορεύεται αὐτοῦ εἰς τὴν καρδίαν), but the stomach or belly (ἀλλ’ εἰς τὴν κοιλίαν). From the stomach, it flowed out in a bowel movement that ended up in a sewer, latrine, or dung heap (καὶ εἰς τὸν ἀφεδρῶνα ἐκπορεύεται). There was a famous saying that it is harder to sell corn after it has been eaten by a pig than before it was eaten. Whatever went into your mouth would end up in a defecation anyway. Thus, Jesus declared that all kinds of foods were cleansed or made clean (καθαρίζων πάντα τὰ βρώματα). This would have been a major rejection of Jewish Torah law and the use of kosher food, since there was a major distinction between clean and unclean foods. This saying of Mark about no more unclean foods was not in Matthew who was writing to a Jewish Christian audience, but it is here for this gentile Christian audience. Luke omitted the whole question.
There was something similar to this earlier in chapter 7:15. Matthew, chapter 15:11 also has something like this. Mark said that Jesus reprimanded them (καὶ λέγει αὐτοῖς) for their lack of discernment or understanding (Οὕτως καὶ ὑμεῖς ἀσύνετοί ἐστε). Did they not realize that whatever went into a person from outside (οὐ νοεῖτε ὅτι πᾶν τὸ ἔξωθεν εἰσπορευόμενον εἰς τὸν ἄνθρωπον) could not make them impure, unclean or a defiled person (οὐ δύναται αὐτὸν κοινῶσαι). Thus, spiritual purity was more important than physical purity. It is not what you put into your body, such as unclean food, that polluted or defiled a person.
There is something similar to this in Mark, chapter 7:15. Jesus, via Matthew, went back to the problem of impurity, unclean or defiled people. Thus, spiritual purity was more important that physical purity. It is not what you put into or what enters into your mouth (οὐ τὸ εἰσερχόμενον εἰς τὸ στόμα), such as unclean food, that pollutes or defiles a man or a person (κοινοῖ τὸν ἄνθρωπον). Rather, what comes out of your mouth (ἀλλὰ τὸ ἐκπορευόμενον ἐκ τοῦ στόματος τοῦτο), such as words, that defile, pollute or make a man or person unclean (κοινοῖ τὸν ἄνθρωπον). It is not what you put into your mouth that makes you unclean, it is what comes out of your mouth that makes you unclean or defiled.
Hosea told the people of Israel, perhaps at a harvest festival, that they would no longer rejoice and exalt like other countries. They had prostituted themselves. They had departed from their God. They had accepted the prostitute’s pay on the threshing floor. No longer would grain and wine feed them, as the new wine would fail. They were not going to remain in the land of Yahweh. They would be sent to Egypt and Assyria, where they would eat unclean food.
“However, many in Israel stood firm. They were resolved in their hearts not to eat unclean food. They chose to die rather than to be defiled by food or to profane the holy covenant. They did die. Very great wrath came upon Israel.”
Here we have an instance of Jewish martyrs. They were willing to die rather than to eat unclean food. They refused to abuse the holy Mosaic covenant. For that they were killed.