A plant-based diet is a diet based on foods derived from plants, including vegetables, whole grains, nuts, seeds, legumes and fruits, but with few or no animal products. The use of the phrase has changed over time, and examples can be found of the phrase "plant-based diet" being used to refer to vegan diets, which contain no food from animal sources, to vegetarian diets which include eggs and dairy but no meat, and to diets with varying amounts of animal-based foods, such as semi-vegetarian diets which contain small amounts of meat.
As of 1999, it was estimated that "4 billion people live primarily on a plant-based diet", and that "shortage of cropland, freshwater, and energy resources requires that most of the 4 billion people live primarily on a plant-based diet".
Historically, examples can be found of the phrase "plant-based diet" being used to refer to diets with varying amounts of animal-based foods, from none at all (vegan) to small amounts of any kind of meat, so long as the primary focus is on plant-based foods (semi-vegetarian). The 2005 book, The China Study, by T. Colin Campbell, the Jacob Gould Schurman Professor Emeritus of Nutritional Biochemistry at Cornell University, and his son Thomas M. Campbell II, a physician, tended to equate a plant-based diet with veganism, although at points the book describes people having a "mostly" plant-based diet. Vegan wellness writer Ellen Jaffe Jones stated in a 2011 interview:
I taught cooking classes for the national non-profit, Physicians Committee for Responsible Medicine, and during that time, the phrase "plant-based diet" came to be used as a euphemism for vegan eating, or "the 'v' word." It was developed to take the emphasis off the word vegan, because some associated it with being too extreme a position, sometimes based exclusively in animal rights versus a health rationale.
More recently a number of authoritative resources have used the phrase "plant-based diet" to refer to diets including varying degrees of animal products, defining "plant-based diets" as, for example "diets that include generous amounts of plant foods and limited amounts of animal foods", and as diets "rich in a variety of vegetables and fruits, legumes, and minimally processed starchy staple foods and limiting red meat consumption, if red meat is eaten at all". Others draw a distinction between "plant-based" and "plant-only".
In various sources, "plant-based diet" has been used to refer to:
From 2017 reviews, a plant-based diet reduced total and LDL cholesterol, with further evidence that shifting plant protein consumption to more than 50% of total protein intake may lower the risk of cardiovascular diseases, although further clinical research was recommended. A diet high in fruits and vegetables may decrease the risk of high blood pressure, stroke, and colorectal cancer. A vegetarian diet may also help with weight loss.
Although herbivory (reliance on diet entirely of plants) was long thought to be a Mesozoic phenomenon, evidence of it is found as soon as the fossils which could show it. Within less than 20 million years after the first land plants evolved, plants were being consumed by arthropods. Herbivory among four-limbed terrestrial vertebrates, the tetrapods developed in the Late Carboniferous (307 - 299 million years ago). Early tetrapods were large amphibious piscivores. While amphibians continued to feed on fish and insects, some reptiles began exploring two new food types: the tetrapods (carnivory) and plants (herbivory).
Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation. In contrast, a complex set of adaptations was necessary for feeding on highly fibrous plant materials.
Quite often, mainly herbivorous creatures will eat small quantities of animal-based food when it becomes available. Although this is trivial most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks insects while food is most needed for growth.
On close inspection it appears that nectar-feeding birds such as sunbirds rely on the ants and other insects that they find in flowers, not for a richer supply of protein, but for essential nutrients such as Vitamin B12 that are absent from nectar. Similarly, monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit. When to refer to such animals as omnivorous or otherwise, is a question of context and emphasis, rather than of definition.
Humans are omnivorous, capable of consuming diverse plant and animal foods. Fossil evidence from wear patterns on teeth indicates the possibility that early hominids like robust australopithecines and Homo habilis were opportunistic omnivores, generally subsisting on a plant-based diet, but supplementing with meat when possible.
A plant-based diet is not necessarily a vegetarian diet. Many people on plant-based diets continue to use meat products and/or fish but in smaller quantities.
... a plant-based diet, which we define as a regimen that encourages whole, plant-based foods and discourages meats, dairy products, and eggs as well as all refined and processed foods.
Since the evolutionary split between homininis and pongids approximately seven million years ago, the available evidence shows that all species of hominins ate an omnivorous diet composed of minimally processed, wild-plant, and animal foods