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In theory, the word vegetarianism means abstaining entirely from flesh food including meat of any animals or birds and fish: whereas in practice there are several different variations of the vegetarian diet e.g. lacto-ovo vegetarians do not eat meat of any animals or birds or fish as such a diet involves the killing of the animals but they include in their diet plant foods, all dairy products and eggs. There are lacto-vegetarians who exclude all animal products including eggs but include dairy products. Although eggs commonly available from the poultry farms do not carry any live embryos, the reason to exclude eggs is mainly the cruelty and torture inflicted on hens in normal poultry farming (see chapter V - Ethical / Spiritual Aspects).
There are also vegetarians known as vegans who follow a diet mainly of plant based foods and do not even consume milk products. This would include curds, butter, cheese, ghee (popularly called butter oil in western countries), sweets and ice-creams made from milk. The reason for omitting the milk and milk products is mainly the cruel treatment meted out to the cows in most dairy farms. It is a common practice to inject hormones in cows to stimulate and increase milk supply and young calves are also deprived of mother's milk. Some of the vegetarians even do not eat honey as many bees are killed in the process of forced procreation to maintain the beehive and the sustained production of honey.
Many vegetarians also shun the use of fur, leather, wool or silk. Their concern is that many living animals, birds and insects are killed or suffer for the manufacture of these products.
There are four distinct arguments each of them convincing by itself in favour of vegetarianism viz. (1) Physiological (2) Health (3) Economic / Environmental and (4) Ethical /Spiritual / Religious. In fact, many nonvegetarians have switched over to vegetarian diet after having learned about these facts.