What is a vegetarian diet?

A vegetarian diet is defined as an eating pattern that excludes all meat products, including red meat, poultry, and seafood as well as any byproducts of slaughter, such as gelatin.^[1] This definition can be confusing because of a lack of standardization. Variations on the vegetarian diet include the lacto-ovo vegetarian diet, which includes dairy products and eggs, and lacto-vegetarian and ovo-vegetarian, which include only dairy products or only eggs, respectively. Some people who eat fish and other seafood products — usually called a pescatarian diet — also refer to their diet as vegetarian, although this is not within the usual definition. Other types of diets that are sometimes grouped in with the vegetarian diet include the flexitarian diet — a diet that focuses on including mostly plant-based foods but allows animal products in moderation — and the semivegetarian diet that also focuses on plant-based foods and excludes red meat products but still includes fish, poultry, or both.^[2][1][3][4]

Within research, vegetarian and vegan diets are often studied together or referred to interchangeably, which can introduce confusion. Vegan diets are different from vegetarian diets in that they do not include any animal products (no meat, eggs, seafood, poultry, dairy products, or honey), and people who follow a vegan lifestyle often avoid animal products outside of food, such as leather goods, wool, or fur.