Some people do not eat various specific foods and beverages in conformity with various religious, cultural, legal or other societal prohibitions. Many of these prohibitions constitute taboos. Many food taboos and other prohibitions forbid the meat of a particular animal, including mammals, rodents, reptiles, amphibians, fish, molluscs, crustaceans and insects, which may relate to a disgust response being more often associated with meats than plant-based foods. Some prohibitions are specific to a particular part or excretion of an animal, while others forgo the consumption of plants or fungi.
Some food prohibitions can be defined as rules, codified by religion or otherwise, about which foods, or combinations of foods, may not be eaten and how animals are to be slaughtered or prepared. The origins of these prohibitions are varied. In some cases, they are thought to be a result of health considerations or other practical reasons; in others, they relate to human symbolic systems.
Some foods may be prohibited during certain religious periods (e.g., Lent), at certain stages of life (e.g., pregnancy), or to certain classes of people (e.g., priests), even if the food is otherwise permitted. On a comparative basis, what may be declared unfit for one group may be perfectly acceptable to another within the same culture or across different cultures. Food taboos usually seem to be intended to protect the human individual from harm, spiritually or physically, but there are numerous other reasons given within cultures for their existence. An ecological or medical background is apparent in many, including some that are seen as religious or spiritual in origin. Food taboos can help utilizing a resource more efficiently, but when applied to only a subsection of the community, a food taboo can also lead to the monopolization of a food item by those exempted. A food taboo acknowledged by a particular group or tribe as part of their ways, aids in the cohesion of the group, helps that particular group to stand out and maintain its identity in the face of others and therefore creates a feeling of "belonging".
Five tribes of Amazonian Indians who share the same upland rainforest, have strict food preferences and food taboos which set each tribe apart from its neighbours -- the Parakana people eat roasted tapir, whilst their neighbours, the Arara people, say that tapir is disgusting and prefer monkey. The differences in preference cannot be explained by environmental differences, but seem to arise from the same kind of psychological need to distinguish ones' own group, a kind of "badge", that also lead each tribe to maintain other cultural differences, such as styles of body ornament. Such food taboos would also serve to limit the consumption of a single species throughout its territory, so removing the chance of extinction, and ensure that some preferred food was likely to be available throughout the tribe's range (because it was not eaten by others).
In the Jewish tradition, food is considered "kosher" or not kosher based on the guidelines laid out in the Torah. According to Leviticus 11:3, the criteria for four-footed animals are that they must have divided hooves, entirely cloven feet, and chew the cud. That means sheep, goats and cattle are among the kosher meats, but pigs, horses and camels are not. Fish are kosher as long as they have both fins and scales (Leviticus 11:0) No other kind of seafood is allowed. Most kinds of fowl commonly eaten in western cultures are kosher, including chicken, turkey, pheasant, duck, goose and quail. The biblical list of forbidden birds is essentially a list of scavengers and birds of prey. Eagles, hawks, vultures and the like are examples. Creatures which do not fit neatly into one of these categories are generally unkosher. Lizards, snakes, rodents, bats and most insects are not kosher. The only kosher insects are certain kinds of locust. Another important dietary rule in rabbinic Judaism is that meat and dairy products may not be eaten together. The Bible never explicitly gives such a rule, but it is derived from an obscure verse in Deuteronomy which says not to boil a kid in its mother's milk (Deuteronomy 14:21). Anything found already dead is unclean. During the week of Passover, there is another rule. During the Feast of Unleavened Bread, all traces of leaven must be removed from the home.
International airlines cater to dietary restriction with a number of different types of special meals. A typical list includes: gluten-free, diabetic, low fat, low cholesterol, no salt, low protein, semifluid, liquid, low calorie, high residue (fibre), vegetarian, lactovegetarian, strict vegetarian, fruit, kosher, no carbohydrates, no red meat, no pork/beef, chicken only, no dairy, asian, chinese, etc.