Both Orthodox Jewish (Kashrut) and Islamic halal dietary laws forbid pork, making it a taboo meat. Among Christians, Seventh-day Adventists consider pork taboo, along with other foods forbidden by Jewish law. Many Eastern Orthodox and Oriental Orthodox groups also discourage pork consumption, although, with the exception of the Ethiopian Orthodox Church, the proscription is rarely enforced.
According to Jewish law, pork is but one of the many foods forbidden from consumption. In the strictest sense, it is as forbidden as are horses and shrimp. There are gravest interdictions, like eating milk and meat together. However, pig meat has become a symbol for everything un-kosher, which calls for explanation.
The general guidelines given in Leviticus are that a "walking" animal is kosher only if it both chews its cud and has cloven hooves. However, the pig is the only animal to have cloven hooves but doesn't chew its cud: its external aspect makes it appear kosher, while it is not, making it a symbol of hypocrisy.
During the persecutions of Antiochus IV Epiphanes, the Greeks forced the Jews to slaughter pigs in the Jerusalem temple, which did not improve the image of pork. Moreover, the Roman legion X Fretensis, that undertook to destruction of the Jerusalem Temple in 68, had a boar for an emblem, sealing its fate as a symbol of everything contrary to Judaism.
Maimonides, the Jewish philosopher and legal codifier, who was also court physician to the Muslim sultan Saladin in the twelfth century, argued that it was a good thing to prohibit pig meat because he perceived that keeping pigs involved uncleanliness.
There is no medical evidence supporting this early notion, although in 1859, a clinical study suggested a connection between undercooked pork and trichinosis. This caused a period of unrest for some Jews, as some began to argue that pork was safe to eat so long as it was fully cooked. Orthodox Jews, however, were appalled at this and insisted that there was some other divine meaning behind kosher law. A third view is that the restriction is arbitrary, a way to test the faith.
The cultural materialistic anthropologist Marvin Harris thinks that the main reason was ecological-economical. Pigs require water and shady woods with seeds, but those conditions are scarce in Israel and Arabia. They cannot forage grass like ruminants. Instead, they compete with humans for expensive grain. Unlike many other forms of livestock, pigs are omnivorous scavengers, eating virtually anything they come across, including carrion and refuse. This was deemed unclean, hence a Middle Eastern society keeping large stocks of pigs would destroy their ecosystem. Harris points out how, while the Hebrews are also forbidden to eat camels and fish without scales, Arab nomads couldn't afford to starve in the desert while having camels around.
He also points to Albania where a partition is established: Christians keep pigs and live in the oak woods, while Muslims keep goats and live in places that the foraging habits of goats keep unforested.
Some food psychologists point out the similarity between the Mosaic food laws as laid out in Leviticus and the natural 'disgust' reaction that all people generally show to unfamiliar meats (see the work of Paul Rozin). That suggests that the food taboos were a codification of existing practice rather than the imposition of a new rule, an attempt to give a religious explanation for an existing state of affairs in which the early Israelites did not eat pork etc. while other groups they knew did.
A similar prohibition is repeated in the Bible in the book of Isaiah chapter 65 verse 2-5.
Muslims consider the eating of pork to be forbidden, with a limited exception to avoid starvation. The Islamic taboo tends to come under scrutiny in places where it is not common, especially when it interferes with those who are unaware or do not follow it. In many cases, the prohibition is extended from consumption to the handling of pork products, creating issues in grocery, shipping, and restaurant environments.