There are hundreds if not thousands of laws surrounding kashrut. The key rules are:
1. Animals must have both split hooves and chew their cud.
2. Fish must have scales and fins.
3. Birds must not be hunters/scavengers and must not be one of the forbidden species specified in the Torah.
4. Meat and dairy must be kept completely separate.
5. Animals cannot display any sign of injury and disease.
6. Animals and birds must be slaughtered in a specific manner and drained of all blood.
7. Consumption of blood is forbidden.
Food laws are not important at all. They are simply a supersticion and no harm will come to anybody eating pork or shellfish.
Jewish answer:
The Jewish dietary laws were never represented as a defense against physiological harm. It is a mistake to think that nothing has any importance unless it can harm you, and to ignore the entire other half of the world, full of things that can benefit you even though you can easily live your life without them.
The 'reason' for the dietary laws is stated in the source text (Leviticus ch.11), immediately following the laws themselves. It's hardly ever quoted, obviously because it's so hard to comprehend. The reason is: In order to be holy.
Books can be written, and certainly have been, on the subject: Is it possible that the stuff you put into your body several times a day for your entire life might possibly have some influence on the kind of person you turn out to be? God states in the Torah (ibid.) that the answer is yes.
The dietary laws are commanded in the Torah. The purpose of them is to make the follower holy, but there are also other modern interpretations.
There are no Catholic dietary laws.
some do not eat certain meats
No. A pig is a split hoofed animal and that is against the dietary laws.
Kosher Laws
Christianity, Judasim, Islam and Baha'i.
The core rules that Jewish dietary laws are based on are found in the Torah. The actual dietary laws, called 'kashrut', are found in the Talmud.
Some are vegetarians and others follow the dietary laws in Leviticus 11
Judasim is a religion, not a people. The term is Jewish people.
Christianity doesn't impose any special dietary laws. In fact, the New Testament teaches that commanding to abstain from certain foods is a mark of "departing from the faith." (1 Timothy 4:1-5.)
Some religions with dietary laws include Judaism (Kosher), Islam (Halal), Hinduism (vegetarianism, avoidance of beef for some), and Sikhism (vegetarianism and prohibition against intoxicants). These dietary laws often have spiritual, cultural, and ethical significance for followers.
You have to know the dietary laws and act in accordance to them.
Yes (in ch.14).