Vegetarianism is the practice of abstaining from the consumption of meatred meat, poultry, seafood and the flesh of any other animal; it may also include abstention from by-productsof animal slaughter.

Vegetarianism can be adopted for different reasons. Many object to eating meat out of respect for sentient life. Such ethical motivations have been codified under various religious beliefs, along with the concept of animal rights. Other motivations for vegetarianism are health-related, political, environmental, cultural, aesthetic or economic. There are varieties of the diet as well: an ovo-vegetarian diet includes eggs but not dairy products, a lacto-vegetarian diet includes dairy products but not eggs, and an ovo-lacto vegetarian diet includes both eggs and dairy products. A vegan, or strict vegetarian, diet excludes all animal products, including eggs, dairy, beeswax and honey. Some vegans also avoid animal products such as leather for clothing and goose-fat for shoe polish.

Various packaged or processed foods, including cake, cookies, candies, chocolate, yogurt and marshmallows, often contain unfamiliar animal ingredients, and may be a special concern for vegetarians due to the likelihood of such additions. Often, products are reviewed by vegetarians for animal-derived ingredients prior to purchase or consumption. Vegetarians vary in their feelings regarding these ingredients, however. For example, while some vegetarians may be unaware of animal-derived rennet's role in the usual production of cheese and may therefore unknowingly consume the product, other vegetarians may not take issue with its consumption.

Semi-vegetarian diets consist largely of vegetarian foods, but may include fish or poultry, or sometimes other meats, on an infrequent basis. Those with diets containing fish or poultry may define meat only as mammalian flesh and may identify with vegetarianism. A pescetarian diet has been described as "fish but no other meat". The common use association between such diets and vegetarianism has led vegetarian groups such as the Vegetarian Society to state that diets containing these ingredients are not vegetarian, due to fish and birds being animals.

Varieties of vegetarianism

There are a number of types of vegetarianism, which exclude or include various foods.

  • Ovo vegetarianism includes eggs but not dairy products.
  • Lacto vegetarianism includes dairy products but not eggs.
  • Ovo-lacto vegetarianism (or lacto-ovo vegetarianism) includes animal/dairy products such as eggs, milk, and honey.
  • Veganism excludes all animal flesh and products, such as milk, honey, and eggs, as well as items refined or manufactured through any such product, such as bone-char refined white sugar or animal-tested baking soda.
  • Raw veganism includes only fresh and uncooked fruit, nuts, seeds, and vegetables. Vegetables can only be cooked up to a certain temperature.
  • Fruitarianism permits only fruit, nuts, seeds, and other plant matter that can be gathered without harming the plant.
  • Sattvic diet (also known as yogic diet), a plant based diet which may also include dairy (not eggs) and honey, but excludes anything from the onion or leek family, red lentils, durian fruit, mushrooms, blue cheeses, fermented foods or sauces, alcoholic drinks and often also excludes coffee, black or green tea, chocolate, nutmeg or any other type of stimulant such as excess sharp spices.
  • Buddhist vegetarianism. Different Buddhist traditions have differing teachings on diet, which may also vary for ordained monks and nuns compared to others. Many interpret the precept 'not to kill' to require abstinence from meat, but not all. In Taiwan, su vegetarianism excludes not only all animal products but also vegetables in the allium family (which have the characteristic aroma of onion and garlic): onion, garlic, scallions, leeks, chives, or shallots.
  • Jain vegetarianism includes dairy but excludes eggs and honey, as well as root vegetables.
  • Macrobiotic diets consist mostly of whole grains and beans.

Within the 'ovo-' groups, there are many who refuse to consume fertilized eggs (with balut being an extreme example); however, such distinction is typically not specifically addressed.

Some vegetarians also avoid products that may use animal ingredients not included in their labels or which use animal products in their manufacturing; for example, sugars that are whitened with bone char, cheeses that use animal rennet (enzymes from animal stomach lining), gelatin (derived from the collagen inside animals' skin, bones and connective tissue), some cane sugar (but not beet sugar) and apple juice/alcohol clarified with gelatin or crushed shellfish and sturgeon, while other vegetarians are unaware of or do not mind such ingredients.

Individuals may label themselves "vegetarian" while practicing a semi-vegetarian diet, as some dictionary definitions describe vegetarianism as including the consumption of fish, or only include mammalian flesh as part of their definition of meat, while other definitions exclude fish and all animal flesh. In other cases, individuals may describe themselves as "flexitarian" These diets may be followed by those who reduce animal flesh consumed as a way of transitioning to a complete vegetarian diet or for health, ethical, environmental, or other reasons. Semi-vegetarian diets include:

  • Pescetarianism, which includes fish and possibly other forms of seafood;
  • Pollotarianism, which includes chicken and possibly other poultry;
  • "Pollo-pescetarian", which includes poultry and fish, or "white meat" only;
  • Macrobiotic diet consisting mostly of whole grains and beans, but may sometimes include fish.

Semi-vegetarianism is contested by vegetarian groups, such as the Vegetarian Society, who state that vegetarianism excludes all animal flesh.

Health effects

In prospective studies of adults, compared to non-vegetarian eating patterns, vegetarian-style eating patterns have been associated with improved health outcomes—lower levels of obesity, a reduced risk of cardiovascular disease, and lower total mortality. Several clinical trials have documented that vegetarian eating patterns lower blood pressure.

On average, vegetarians consume a lower proportion of calories from fat (particularly saturated fatty acids), fewer overall calories, more fiber, potassium, and vitamin C, than do non-vegetarians. Vegetarians generally have a lower body mass index. These characteristics and other lifestyle factors associated with a vegetarian diet may contribute to the positive health outcomes that have been identified among vegetarians.

Dietary Guidelines for Americans, 2010 – A report issued by the U.S. Department of Agriculture and the U.S. Department of Health and Human Service.

Scientific endeavors in the area of vegetarianism have shifted from concerns about nutritional adequacy to investigating health benefits and disease prevention.TheAcademy of Nutrition and Dietetics and Dietitians of Canada have stated that at all stages of life, a properly planned vegetarian diet is "healthful, nutritionally adequate, and provides health benefits in the prevention and treatment of certain diseases". Large-scale studies have shown that mortality from ischaemic heart disease was 30% lower among vegetarian men and 20% lower among vegetarian women than in non-vegetarians. Vegetarian diets offer lower levels of saturated fat, cholesterol and animal protein, and higher levels of carbohydrates, fibre, magnesium, potassium, folate, and antioxidants such as vitamins C and E and phytochemicals.

Vegetarians tend to have lower body mass index, lower levels of cholesterol, lower blood pressure, and less incidence of heart disease, hypertension, type 2 diabetes,renal disease, metabolic syndrome, dementias such as Alzheimer's disease and other disorders. Non-lean red meat, in particular, has been found to be directly associated with increased risk of cancers of the esophagus, liver, colon, and the lungs. Other studies have shown no significant differences between vegetarians and non-vegetarians in mortality from cerebrovascular disease, stomach cancer, colorectal cancer, breast cancer, or prostate cancer. A 2010 study compared a group of vegetarian and meat-eating Seventh-day Adventists in which vegetarians scored lower on depression tests and had better mood profiles.

The relationship between vegetarian diet and bone health remains unclear. According to some studies, a vegetarian lifestyle can be associated with vitamin B12 deficiencyand low bone mineral density. However, a study of vegetarian and non-vegetarian adults in Taiwan found no significant difference in bone mineral density between the two groups. Other studies, exploring animal protein's negative effects on bone health, suggest that vegetarians may be less prone to osteoporosis than omnivores, as vegetarian subjects had greater bone mineral density and more bone formation.

The China-Cornell-Oxford Project, a 20-year study conducted by Cornell University, the University of Oxford, and the government of China has established a correlation between the consumption of animal products and a variety of chronic illnesses, such as coronary heart disease, diabetes, and cancers of the breast, prostate and bowel(see The China Study).