Compare Mark 7:18 and Tosefta Mikvaot 7:3

"... Although this distinction between the domains of tohorah and kashrut has been long noted by scholars, it, unfortunately, has been and continues to be disregarded by interpreters of Mark 7:1–23. As Daniel Boyarin puts it, ‘It is this confusion between the laws of [ritual] defilement (ṭumʾah) and the laws of kashrut that has generated the persistent misreading of the pericope.’ The context of this passage makes abundantly clear that what is at stake is specifically ritual impurity: the comments about immersion, cleansing cups and washing hands in 7:2–5 are practices related to the domain of tohorah, not kashrut. The issue is not that some of Jesus’ disciples are eating non-kosher animals; rather, by not washing their hands they put themselves in danger of eating permitted food that had become ritually defiled by hands that may have already contracted impurity from another source. Perhaps the clearest articulation of the distinction between tohorah and kashrut emerges in the following statement from Rashi’s commentary on b. Shabbat 13b: ‘According to the Torah there is no food that defiles a human who eats it except the carrion of a pure bird … and even less so food defiled by touching a primary source of impurity … but they [the rabbis] decreed this rule.’ While I will deal with the carrion passages below, it is important to note that Rashi claims that only the ingestion of pure (that is, kosher/permitted) bird carrion defiles one who eats it. This entails that the Torah does not rule that eating prohibited animals ritually defiles. And, as Rashi further indicates here, the notion that ingesting ritually defiled permitted food can defile a person is a decree not from the Torah but from the rabbis ..."