Vegetarianism, the theory or practice of living solely upon vegetables, fruits, grains, and nuts—with or without the addition of milk products and eggs—generally for ethical, ascetic, environmental, or nutritional reasons. All forms of flesh (meat, fowl, and seafood) are excluded from all vegetarian diets, but many vegetarians use milk and milk products; those in the West usually eat eggs also, but most vegetarians in India exclude them, as did those in the Mediterranean lands in Classical times. Vegetarians who exclude animal products altogether (and likewise avoid animal-derived products such as leather, silk, and wool) are known as vegans. Those who use milk products are sometimes called lacto-vegetarians, and those who use eggs as well are called lacto-ovo vegetarians. Among some agricultural peoples, flesh eating has been infrequent except among the privileged classes; such people have rather misleadingly been called vegetarians.
Deliberate avoidance of flesh eating probably first appeared sporadically in ritual connections, either as a temporary purification or as qualification for a priestly function. Advocacy of a regular fleshless diet began about the middle of the 1st millennium bc in India and the eastern Mediterranean as part of the philosophical awakening of the time. In the Mediterranean, avoidance of flesh eating is first recorded as a teaching of the philosopher Pythagoras of Samos (c. 530 bc), who alleged the kinship of all animals as one basis for human benevolence toward other creatures. From Plato onward many pagan philosophers (e.g., Epicurus and Plutarch), especially the Neoplatonists, recommended a fleshless diet; the idea carried with it condemnation of bloody sacrifices in worship and was often associated with belief in the reincarnation of souls and, more generally, with a search for principles of cosmic harmony in accord with which human beings could live. In India, followers of Buddhism and Jainism refused on ethical and ascetic grounds to kill animals for food. Human beings, they believed, should not inflict harm on any sentient creature. This principle was soon taken up in Brahmanism and, later, Hinduism and was applied especially to the cow. As in Mediterranean thought, the idea carried with it condemnation of bloody sacrifices and was often associated with principles of cosmic harmony.
In later centuries the history of vegetarianism in the Indic and Mediterranean regions diverged significantly. In India itself, though Buddhism gradually declined, the ideal of harmlessness (ahimsa), with its corollary of a fleshless diet, spread steadily in the 1st millennium ad until many of the upper castes, and even some of the lower, had adopted it. Beyond India it was carried, with Buddhism, northward and eastward as far as China and Japan. In some countries, fish were included in an otherwise fleshless diet.
West of the Indus the great monotheistic traditions were less favourable to vegetarianism. The Hebrew Bible, however, records the belief that in paradise the earliest human beings had not eaten flesh. Ascetic Jewish groups and some early Christian leaders disapproved of flesh eating as gluttonous, cruel, and expensive. Some Christian monastic orders ruled out flesh eating, and its avoidance has been a penance and a spiritual exercise even for laypersons. Many Muslims have been hostile to vegetarianism, yet some Muslim Sufi mystics recommended a meatless diet for spiritual seekers.
The 17th through 19th centuries
The 17th and 18th centuries in Europe were characterized by a greater interest in humanitarianism and the idea of moral progress, and sensitivity to animal suffering was accordingly revived. Certain Protestant groups came to adopt a fleshless diet as part of the goal of leading a perfectly sinless life. Persons of diverse philosophical views advocated vegetarianism; for example, Voltaire praised it, and Percy Bysshe Shelley and Henry David Thoreau practiced the diet. In the late 18th century the utilitarian philosopher Jeremy Bentham asserted that the suffering of animals, like the suffering of humans, was worthy of moral consideration, and he regarded cruelty to animals as analogous to racism.
Vegetarians of the early 19th century usually condemned the use of alcohol as well as flesh and appealed as much to nutritional advantages as to ethical sensibilities. As before, vegetarianism tended to be combined with other efforts toward a humane and cosmically harmonious way of life. Although the vegetarian movement as a whole was always carried forward by ethically inclined individuals, special institutions grew up to express vegetarian concerns as such. The first vegetarian society was formed in England in 1847 by the Bible Christian sect, and the International Vegetarian Union was founded tentatively in 1889 and more enduringly in 1908.
By the early 20th century vegetarianism in the West was contributing substantially to the drive to vary and lighten the nonvegetarian diet. In some places a fleshless diet was regarded as a regimen for specific disorders. Elsewhere, notably in Germany, it was considered as one element in a wider conception of vegetarianism, which involved a comprehensive reform of life habits in the direction of simplicity and healthfulness.
In the second half of the 20th century, the work of the Australian ethical philosopher Peter Singer inspired a revival of philosophical interest in the practice of vegetarianism and the larger topic of animal rights. Singer offered utilitarian arguments to support his contention that modern methods of raising and slaughtering animals for human food (“factory farming”) are morally unjustified; his arguments also applied to other traditional ways in which humans use animals, including as experimental subjects in medical research and as sources of entertainment. Singer’s work provoked much vexed discussion of the question of whether the traditional treatment of animals is justified by any “morally relevant” differences between animals and humans.
Meanwhile, other debates centred on the question of whether a fleshless diet, and specifically a vegan one, provides all the nutrients necessary for human health. In the West, for example, it was long a common belief that humans cannot obtain enough protein from a diet based solely on plant foods. However, nutritional studies conducted in the 1970s cast doubt on this claim, and it is seldom advanced today. A more recent issue is whether a vegan diet can provide enough vitamin B12, which humans need in tiny amounts (1 to 3 micrograms per day) to produce red blood cells and to maintain proper nerve functioning. Popular vegan sources of B12 include nutritional yeast, certain fortified foods made without animal products (such as cereals and soy milk), and vitamin supplements.
By the early 21st century vegetarian restaurants were commonplace in many Western countries, and large industries were devoted to producing special vegetarian and vegan foods (some of which were designed to simulate various kinds of flesh and dairy products in form and flavour). Today many vegetarian societies and animal rights groups publish vegetarian recipes and other information on what they consider to be the health and environmental benefits and the moral virtues of a fleshless diet.