Where do Jewish food laws come from?

Answer 1

Jewish law regarding food, known as kashrut, comes from the Torah, the Jewish holy book that also forms the earliest parts of the Christian Bible - which is some groups of Christians also apply them to what they will and will not eat.

Some of the laws seem to have some ethical or practical purpose, for example the laws governing the slaughter of animals - shechita - appear designed to avoid causing the animal suffering (and indeed, shechita was the most humane way to slaughter animals for many centuries - whether or not it remains so now that modern stunning methods have been developed remains a point of much discussion). However, the vast majority of kashrut is consider chukim - that is, laws for which no reason is offered in the Torah and which are assumed to be due to some Divine reason beyond the understanding and/or wisdom of human beings.

When a new type of food comes onto the market, whether or not is is kosher (ie; acceptable for Jewish consumption) is decided by rabbis who will look for historical precedents. As an example, turkeys were unknown outside the New World prior to the discovery of America by Columbus. However, the rabbis discovered that the bird is very similar in appearance to another species known as the Fowl of India which was known to fall into the category of birds considered kosher and so the turkey too was deemed kosher.

Answer 2

1) the Torah (see for example Deuteronomy ch.14).

2) the Talmud, which elucidates the details of the Torah's brief verses. The Talmudic tractate of Chullin is specifically dedicated to this topic.

Answer 3

the Torah.