A plant-based diet is a diet consisting mostly or entirely of plant-based foods. Plant-based diets encompass a wide range of dietary patterns that contain low amounts of animal products and high amounts of plant products such as vegetables, fruits, whole grains, legumes, nuts and seeds. They do not need to be vegan or vegetarian but are defined in terms of low frequency of animal food consumption. Terminology Origin of the term "plant-based diet" is attributed to Cornell University nutritional biochemist T. Colin Campbell who presented his diet research at the US National Institutes of Health in 1980. Campbell's research about a plant-based diet extended from The China Project, a decade-long study of dietary practices in rural China, giving evidence that a diet low in animal protein and fat, and high in plant foods, could reduce the incidence of several diseases. In 2005, Campbell and his son published The China Study, a best-selling book emphasizing the potential health benefits of a plant-based diet. Campbell also used the plant-based concept to educate consumers about how eating meat had significant environmental consequences. Some authors draw a distinction between diets that are "plant-based" or "plant-only". A plant-based diet may be defined as consuming plant-sourced foods that are minimally processed. A review analyzing the use of the term plant-based diet in medical literature found that 50% of clinical trials use the term interchangeably with vegan, meaning that the interventional diet did not include foods of animal origin. 30% of studies included dairy products and 20% meat. In 2021, the World Health Organization (WHO) stated that "plant-based diets constitute a diverse range of dietary patterns that emphasize foods derived from plant sources coupled with lower consumption or exclusion of animal products. Vegetarian diets form a subset of plant-based diets, which may exclude the consumption of some or all forms of animal foods." The WHO lists, flexitarian, lacto-vegetarian, lacto-ovo vegetarian, ovo-vegetarian, pescatarian and vegan diets as plant-based. Motivation and prevalence As of the early 21st century, some 4 billion people are estimated to live primarily on a plant-based diet, some by choice and some because of limits caused by shortages of crops, fresh water, and energy resources. Main motivations to follow a plant-based diet appear to be health aspirations, taste, animal welfare, environmental concern, and weight loss. Health research Plant-based diets are of interest in preventing and managing chronic diseases. Diet quality Not all plant-based foods are