Vegetarianism is the practice of avoiding dietary consumption of animal flesh, and in some cases animal products. Vegetarianism has been practised throughout human history for a variety of reasons, and its motivation and definition remain controversial today. An individual's decision to adopt vegetarianism may be influenced by a combination of different factors.
One oft-cited reason for adopting vegetarianism is ethics. Ethical vegetarianism is associated with the arguments of animal rights activists that humans should not breed and kill other animals for human consumption. Some religions, for example (certain forms of) Buddhism, Hinduism, Taoism and Jainism, similarly teach that all life should be valued and not wilfully destroyed for personal greed.
Another justification for vegetarianism is environmental or ecological. Particularly since the Industrial Revolution, machinery has enabled people to change their environment at a rate with which natural processes cannot keep up. In particular, the use of large areas of land for livestock farming, and large-scale fishing in the oceans, have fundamentally affected animal and marine populations which used to co-exist in symbiosis. Livestock production is also often linked to de-forestation. In environmental terms the cost of raising a pound of beef is many times the cost of growing a pound of beans.
A third justification is health. Statistics indicate that people on vegetarian diets have lower incidence of heart disease, cancer and osteoporosis. Of course the statistics could be the result of other socio-economic factors, but many believe that a vegetable based diet is more healthy than a diet where most of the calories come from meat. Researchers like Dean Ornish have had remarkable results treating heart disease patients with strictly vegetarian diet, exercise and stress reduction programs.
There are also nutritional considerations which encourage diets emphasising fruit, vegetables and cereals and minimising meat and fat intake.
Finally, there are aesthetic reasons: some find meat (particularly raw) disgusting.
It remains debatable whether people who eat seafood or poultry can be called 'vegetarian'. Foregoing 'red meats' such as beef or lamb may be a sound nutritional decision, but continuing to eat fish and chicken, for example, does not address the other common concerns of vegetarians which are discussed above.
In everyday language, 'vegetarianism' is usually synonymous with ovo-lacto vegetarianism, which tolerates the consumption of animal products that can be gathered without harming animals, such as eggs and milk. Vegetarians may recognise that all methods of deriving food from animals involves some exploitation, and refuse to eat cheese made with animal-based enzymes or eggs produced by battery farms.
More extreme than ovo-lacto vegetarians are vegans and fructarians. Vegans exclude all animal products, such as eggs, milk and honey, from their diet and lifestyle. Fructarians will not eat plant matter that cannot be gathered without harming the plant; thus they will only eat fruits, nuts and seeds, which include tomatoes, cucumbers, pumpkins, etc.
While vegetarianism is commonly associated with dietary habits, many ethical and environmental vegetarians (in common with animal rights and Green movements) try to minimise the harm done to animals in other aspects of their lives. A vegetarian lifestyle includes avoiding the use of clothing and accessories made of leather, skin or fur.
Anecdotal evidence suggests that some vegetarians began by gradually reducing their meat intake to the point where meat was no longer a necessary part of their diet. Related to nutritional concerns is uncertainty about the nature of genetically modified food. For these reasons some people restrict themselves to eating organic food products. While organic diets are not necessarily vegetarian, organic food principles and vegetarianism are both concerned with reducing the amount of artificial processing applied to food.
Mention: protein/amino acid problem, animals were created for being eaten, animals eat animals, animals don't suffer, plants suffer too etc.
Vitamin B12 deficiency can result from veganism. While just about all animal based foods contain useful quantities of B12, there are no good plant based sources. (B12 supplements such as vitamin pills are often prepared from abattoir waste, although there are an increasing number of brands that contain no animal products.) B12 is stored in the body for many months, so B12 deficiency symptoms do not appear immediately on embarking on a pure vegan diet, but can eventually be severe.
Other nutritional arguments against vegetarianism are as follows: ...
These arguments, in the opinion of someone who isn't identifying him or herself, don't seem to be very strong.
Some important nutrients (protein, fat, vitamins A, D, and K, and "vitamin E") are present in good quantities in meat, but with some care a vegetarian diet with plenty of all of these can be designed. Meat protein apparently has a good mix of amino acids for human nutritional needs, but again, a good enough mix can be had from plant foods. Wheat has a just about ideal mix (thought its total protein content is fairly low) and other plant protein sources are not too bad, especially if there is a wide variety of plants eaten.
See also Peter Singer
The Food Revolution, John Robbins, ISBN: 1573247022
Physicians Committee for Responsible Medicine http://www.pcrm.org/health/index.html