APA Dictionary of Psychology

a prescribed course of eating food that is plant-based and, to varying degrees, excludes meat, fowl, seafood, and anything made with or derived from these ingredients. There are several variations of this kind of diet; veganism, for example, excludes the consumption or use of any animal products even if the animal is not harmed in the harvest of its products (e.g., honey, eggs). Among the reasons people choose a vegetarian diet are health (e.g., to lower cholesterol, to lose weight), cultural beliefs (e.g., certain Indian and Buddhist teachings prohibit the slaughter of animals), environmental concerns (e.g., raising animals for human consumption is a strain on the world’s food system and argued to contribute to climate change), and ethical concerns (e.g., factory farming conditions can be considered cruel to the animals). A well-planned vegetarian diet can be nutritionally sound and healthful, although vegetarians—that is, people who follow a plant-based diet—must be careful to find plant sources of necessary nutrients, such as vitamin B₁₂, vitamin D, zinc, iron, and protein.