Defintions of vegetarianism(s):
- "A diet that omits animal products, based instead on fruits, vegetables, legumes, and grains."
- Vegan: Omits all animal products from diet and lifestyle, including leather. Strictest forms omit honey ("non-honey vegan," NHV) and yeast.
- Ovo-lacto vegetarian: Omits meat, poultry, and fish from diet but consumes dairy and eggs.
- Piscetarian: Omits meat and poultry, but consumes fish, dairy, and eggs.
Getting all the nutrition you need as a vegetarian, and even as a strict vegan, is easy provided you eat a varied, well-balanced diet full of fruits, vegetables, legumes, and grains. Variety is key.
Pay attention to:
- Protein: There are 8 amino acids that our bodies can't produce, so we must therefore eat them. It's easiest to find these necessary proteins in animal products (including dairy, fish, and eggs), but they are also all present in plants as well. The problem is that not all proteins are found in every plant, so therefore you have to make sure you eat varied plant matter (like rice and beans) to be sure to get all of them into your diet. Tofu and other soy products contain all 8 "essential" amino acids.
- B-12: B-12 is a necessary vitamin that is found in only a few types of plants. These include yeast, sea vegetables (dulse, kelp, nori), and soy. You may want to take a vitamin supplement if you don't eat the above regularly.
- Calcium: Calcium is in your green leafy veggies! The calcium found in plants is a smaller molecule than that found in milk, and is therefore also more easily absorbed by your body. Calcium can also be found in dairy and enriched orange juice (though some enriched OJ is not vegan). Many herbs are rich in calcium.
- Iron: Iron is also in your green leafy veggies! Also: whole grains, soy, some beans, some nuts, and some fruits. You can buy an iron skillet to cook in, and some of the iron will be absorbed into your food.
There are about as many reasons to go veg as there are vegetarians. Below are some common ones.
- Your health: Fatty meat products contribute to heart disease, cancer, and obesity. Goveg.com reports vegetarians live 6-10 years longer than omnivores. Avoiding meat also avoids all the hormones and antibiotics fed to cows and chickens, as well as diseases like Mad Cow and salmonella (however, salmonella, hormones, and antibiotics can be found in ovo-lacto fare).
- Animal rights: Animal mistreatment and abuse is common practice at many factory farms and slaughterhouses where animals are kept in close quarters, often with their manure, in such conditions that the only way they stay healthy enough to be made into edibles is to bed fed a constant diet of antibiotics. Veal calves (the male babies of dairy cows, and therefore a product of the milk industry) are kept in pens too small to allow for any movement, which keeps their flesh tender and unmuscled. Chickens used for eggs and poultry are kept stacked in wire cages with no room to move; the feces of those on top land on the hens below. Abuse of cattle, pigs, and birds is well documented. Fish are often cut open while still alive; they always face suffocation above water, and are often torn by hooks. Fishing nets catch creatures like sea turtles and dophins ("bycatch") that may die before they can be released, assuming the fishing company tries to release them at all.
- Human rights:
- Working conditions at factory farms, slaughterhouses, and fishing boats are dangerous with low pay and varying union support (a NY Times article recently said the unionization of Chicago meat packers is at the level in Upton Sinclair's The Jungle, written in 1906).
- Many industrial packing plants dump their refuse directly into waterways: Perdue, for example, dumps chicken feces into a river that feeds a reservoir downstream, in a town which now suffers high cancer rates. 
- Meat and dairy based diets create an unequal food distribution, as land and vegetable resources are devoted to making meat, which feeds far fewer people than the original land and veggies could have. The meat itself is expensive, and only the wealthy can afford it.
- Religious adherence: Adherents of many religious philosophies, such as Jains and certain types of Hindus, Sikhs, and Buddhists are prohibited from eating meat. Other religions, such as Rastafarianism and Seventh-day Adventism, strongly exhort vegetarianism. Some Christians practice a type of vegetarianism on certain days or during certain seasons; for example, in addition to fasting on Wednesdays and Fridays, Eastern Orthodox Christians have four seasonal fasts where meat, fish, and dairy are forbidden (although shellfish is usually permitted).
- It gives you hippie cred: To truly fit in among the Oberlin militant left, vegeterianism, or, preferably, veganism, is necessary. Failure to conform brings the risk of being considered morally inferior.
...versus an omnivore diet:
- Land use: Eating meat contributes to deforestation as ranchers seek new grazing land. Much slash and burn rainforest deforestation is for beef used by the fats food industry. A vegetarian saves an estimated one acre per year of trees.
- Topsoil: While any intensive farming can lead to erosion, animal products contribute more to loss of topsoil than plants. Farming animals graze the plants holding soil intact and then trample it into either mud or dust, which washes away easily. The manure concentrations often are too high for plants to grow in.
- Fossil fuels: Both plant farming and meat production have high fossil fuel impacts. Tractors, transportation, and processing all use up this non-renewable resource. Currently, over a third the materials and fossil fuels used in the US go to animal products (Motavalli, Jim. "The Case Against Meat." E Magazine. January/February 2002, Vol. XIII, no. 1).
- Water: It takes 60 pounds of water to make one pound of wheat; it takes 2500-6000 pounds of water to make 1 pound of beef. Eating meat wastes and pollutes water, as many animal wastes (1.5 billion tons per year in the US) are dumped into rivers and groundwater.
- Pollution: Growing crops usually involves intensive use of pesticides and herbicides, which can hurt humans who eat the polluted plants and who drink water contaminated by run-off. These can also have detrimental impacts on "non-target" species (e.g. a pesticide killing a harmless insect). Use of fertilizer can cause erosion of topsoil. When fertilizer (or manure) leaks into lakes, the resulting nitrogen spike causes algae to bloom and cover the entire surface of the water, choking out light and killing the fish and plants inside. Yet, animals are fed the grains grown in this manner, as well as antibiotics, which contributes to antibiotic resistant diseases, and animal production contributes toxic waste (feces) pollution on top of this farming pollution.
- General waste: 1 lb beef = 4.8 lbs grain (because the beef must be fed the grain). 1 8 oz steak = 1 cup cooked grains for 40-50 people.
Critiscism and Caveats
"If vegetarianism is better for your heath, the environment, other people, and the animals, why isn't everyone a vegetarian?"
- Meat tastes good: Meat, poultry, and fish are familiar, readily available, and delicious.
- Creativity requirement: If variety is key to vegetarian nutrition, relying only on staple foods results in becming malnourished, tired, and sick. Veg cooking does require some effort and the lazy or pressed for time may not feel up to it, or have the inclination to try.
- Inconvenience and expense: Reading labels to make sure there are no hidden animal ingredients, bringing an extra dish to family gatherings, assuring Mom that you're eating well, and questioning waiters about the broth in their vegetable soup can all be annoying. Buying organic, faux-meat, and faux-leather products is expensive.
- Ignorance: A lot of people are unaware of just how much filling, delicious food exists for vegetarians, or that vegetarian diets can supply people with all the nutrition and calories they need.