[25] Initially centered on abstaining from meat, this concept evolved to include the exclusion of all animal by-products, such as clothing, household items, and medicinal remedies, and extends to doing no harm in thought or action towards all sentient beings, natural habitats or ecosystems.

[26] Greek philosophers associated with the practice include Empedocles, Theophrastus, Plutarch, Plotinus, and Porphyry, along with the Roman poet Ovid and the playwright Seneca the Younger.

[30] Eudoxus of Cnidus, a student of Archytas and Plato, writes, "Pythagoras was distinguished by such purity and so avoided killing and killers that he not only abstained from animal foods, but even kept his distance from cooks and hunters".

[35] Lambe called animal food a "habitual irritation" and argued that "milk eating and flesh-eating are but branches of a common system and they must stand or fall together".

[34]An article in the Society's magazine, the Vegetarian Messenger, in 1851 discussed alternatives to shoe leather, which suggests the presence of vegans within the membership who rejected animal use entirely, not only in diet.

When the request was denied, Donald Watson, secretary of the Leicester branch, set up a new quarterly newsletter, The Vegan News, in November 1944, priced tuppence.

[11][59] According to Joanne Stepaniak, the word vegan was first published independently in 1962 by the Oxford Illustrated Dictionary, defined as "a vegetarian who eats no butter, eggs, cheese, or milk".

In attendance were Donald Watson, Elsie B. Shrigley, Fay K. Henderson, Alfred Hy Haffenden, Paul Spencer and Bernard Drake, with Mme Pataleewa (Barbara Moore, a Russian-British engineer) observing.

Philosopher Gary Steiner argues that it is not possible to be entirely vegan, because animal use and products are "deeply and imperceptibly woven into the fabric of human society".

[207] Ethical vegans may wear clothing items and accessories made of non-animal-derived materials such as hemp, linen, cotton, canvas, polyester, artificial leather (pleather), rubber, and vinyl.

[228][230][236] A 2015 study found that 6 out of 24 commercial vegan pet food brands do not meet the Association of American Feed Control Officials (AAFCO) labeling regulations for amino acid adequacy.

One review reported moderate evidence that adhering to a vegan diet for at least 12 weeks may be effective in individuals with overweight or type 2 diabetes to induce a meaningful decrease in body weight and improve glycemia.

[250] A Cochrane review of randomized controlled trials found that there is "currently insufficient information to draw conclusions about the effects of vegan dietary interventions on cardiovascular disease risk factors".

[255][256] The Academy of Nutrition and Dietetics and Dietitians of Canada say that properly planned vegetarian or vegan diets are appropriate for all life stages, including pregnancy and lactation.

Because data is lacking the DGE does not recommend for or against vegan diets for vulnerable groups like children, young people, elderly and pregnant or breastfeeding women.

[264][265] The Academy of Nutrition and Dietetics consider well-planned vegetarian and vegan diets "appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes.

[266] The position of the Canadian Pediatric Society is that "well-planned vegetarian and vegan diets with appropriate attention to specific nutrient components can provide a healthy alternative lifestyle at all stages of fetal, infant, child and adolescent growth.

[k] As a result of the elimination of all animal products, a poorly planned vegan diet can lead to nutritional deficiencies that counteract its beneficial effects and cause serious health issues,[255][267][268] some of which can only be prevented with fortified foods or dietary supplements.

[255][257] Vitamin B12 supplementation is important because its deficiency can cause blood disorders and potentially irreversible neurological damage; this danger is also one of the most common in poorly planned non-vegan diets.

[l][82]: 62  Philosopher Tom Regan, also a rights theorist, argues that animals possess value as "subjects-of-a-life", because they have beliefs, desires, memory and the ability to initiate action in pursuit of goals.

[82]: 72–73 Philosopher Val Plumwood maintained that ethical veganism is "subtly human-centred", an example of what she called "human/nature dualism", because it views humanity as separate from the rest of nature.

The "faith in the singular efficacy of conjectural education and moral persuasion," Best writes, is no substitute for "direct action, mass confrontation, civil disobedience, alliance politics, and struggle for radical change.

"[274] Sociologist David Nibert of Wittenberg University posits that any movement towards global justice would necessitate not only the abolition of animal exploitation, particularly as a food source for humans, but also transitioning towards a socioeconomic alternative to the capitalist system, both of which dovetail into what he calls the animal–industrial complex.

[311] The report also concluded that livestock farming (mostly of cows, chickens and pigs) affects the air, land, soil, water, biodiversity and climate change.

[313] Paul Watson of the Sea Shepherd Conservation Society called pigs and chicken "major aquatic predators", because livestock eat 40 percent of the fish that are caught.

[324][325] On 8 August 2019, the IPCC released a summary of the 2019 special report which asserted that a shift towards plant-based diets would help to mitigate and adapt to climate change.

[326] A 2022 study found that for high-income nations alone 100 billion tons of carbon dioxide could be removed from the air by the end of the century through a shift to plant-based diets and re-wilding of farmlands.

[340] It connects the use of nonhuman animals with other social justice concerns such as racism, and with the lasting effects of slavery, such as the subsistence diets of enslaved people enduring as familial and cultural food traditions.

"[386][387] Jessica Cruz / Green Lantern, a lead character in the animated series, DC Super Hero Girls is not only pacifist, but also a vegan and environmentalist,[388][389] resulting in her becoming friends with Pam Isley.

[398] Gary Francione ("Animal Welfare, Happy Meat and Veganism as the Moral Baseline", 2012): "Ethical veganism is the personal rejection of the commodity status of nonhuman animals ..."[15] Another early use was by the editor of The Healthian, a journal published by Alcott House, in April 1842: "To tell a man, who is in the stocks for a given fault, that he cannot be so confined for such an offence, is ridiculous enough; but not more so than to tell a healthy vegetarian that his diet is very uncongenial with the wants of his nature, and contrary to reason.