A plant-based diet is a diet of any animal (including humans) based on foods derived from plants, including vegetables, whole grains, 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.
Many people who live on a plant-based diet are thought to do so out of economic necessity. As of 1999 it was estimated that "an estimated 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".
In various sources, "plant-based diet" has been used to refer to:
- Veganism: diet of vegetables, legumes, fruit, grains, nuts, and seeds, but no food from animal sources.
- Vegetarianism: diet of vegetables, legumes, fruit, nuts, etc., that may include eggs and dairy, but no meat.
- Semi-vegetarianism: mostly vegetarian diet with occasional inclusion of meat and/or poultry.
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Evidence supports health benefits from eating fruits and vegetables. For example, a diet high in fruits and vegetables may decrease the risk of high blood pressure, stroke, and colorectal cancer.
A 2013 Nutritional Update for Physicians stated, "Healthy eating may be best achieved with 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." And, "Research shows that plant-based diets are cost-effective, low-risk interventions that may lower body mass index, blood pressure, HbA1C, and cholesterol levels. They may also reduce the number of medications needed to treat chronic diseases and lower ischemic heart disease mortality rates. Physicians should consider recommending a plant-based diet to all their patients, especially those with high blood pressure, diabetes, cardiovascular disease, or obesity."
The quality of the plant foods makes a difference; a meta-analysis of three perspective cohort studies found that "having a diet that emphasized plant foods and was low in animal foods was associated with a reduction of about 20% in the risk of diabetes." And, "Consumption of a plant-based diet that emphasized specifically healthy plant foods was associated with a larger decrease (34%) in diabetes risk, while consumption of a plant-based diet high in less healthy plant foods was associated with a 16% increased diabetes risk."
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.
Modern herbivores and mild omnivory
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, specifically, are omnivorous, capable of consuming a wide variety of plant and animal material. Fossil evidence such as wear patterns on the teeth of early hominids such as robust australopithecines and Homo habilis indicate that they were opportunistic omnivores, generally subsisting on a plant-based diet, but supplementing this diet with meat when possible.
Some nutritional experts believe that early hominids evolved into eating meat as a result of huge climatic changes that took place three to four million years ago, when forests and jungles dried up and became open grasslands and opened hunting and scavenging opportunities.
- Liane Summerfield, Nutrition, Exercise, and Behavior: An Integrated Approach to Weight Management (2011), p. 181-182.
- Philip J Tuso, MD; Mohamed H Ismail, MD; Benjamin P Ha, MD; Carole Bartolotto, MA, RD. "Nutritional Update for Physicians: Plant-Based Diets." The Permanente Journal (Kaiser Permanente). 2013 Spring; 17(2):61-66.
- David Pimentel, Marcia H. Pimentel, Food, Energy, and Society, CRC Press, 2007, p. 67.
- T. Colin Campbell and Thomas M. Campbell II, The China Study (2005).
- The China Study, p. 73; 139.
- Ellen Jaffe Jones, in Michelle Stark, "Wellness experts weigh in on the vegan diet", Tampa Bay Times (May 25, 2015).
- See American Dietetic Association and Dietiticians of Canada, "Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets" (February 16, 2014): " ... plant-based diets, defined as diets that include generous amounts of plant foods and limited amounts of animal foods", and listing the views of other groups.
- Tuso, P; Stoll, SR; Li, WW (2015). "A plant-based diet, atherogenesis, and coronary artery disease prevention.". The Permanente journal. 19 (1): 62–7. doi:10.7812/TPP/14-036. PMC . PMID 25431999.
- Barnard, ND; Levin, SM; Yokoyama, Y (June 2015). "A systematic review and meta-analysis of changes in body weight in clinical trials of vegetarian diets.". Journal of the Academy of Nutrition and Dietetics. 115 (6): 954–69. doi:10.1016/j.jand.2014.11.016. PMID 25620754.
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- Steck, S. E.; Guinter, M; Zheng, J; Thomson, C. A. (2015). "Index-based dietary patterns and colorectal cancer risk: A systematic review". Advances in Nutrition: an International Review Journal. 6 (6): 763–73. doi:10.3945/an.115.009746. PMC . PMID 26567200.
- Satija, Ambika; Bhupathiraju, Shilpa N.; Rimm, Eric B.; Spiegelman, Donna; Chiuve, Stephanie E.; Borgi, Lea; Willett, Walter C.; Manson, JoAnn E.; Sun, Qi (2016-06-14). "Plant-Based Dietary Patterns and Incidence of Type 2 Diabetes in US Men and Women: Results from Three Prospective Cohort Studies". PLOS Med. 13 (6): e1002039. doi:10.1371/journal.pmed.1002039. ISSN 1549-1676. PMC . PMID 27299701.
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"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.
- Jean Louis Flandrin, Massimo Montanari, Albert Sonnenfeld, Food: A Culinary History from Antiquity to the Present (1999), p. 24.
- Timothy Clack, Ancestral Roots: Modern Living and Human Evolution (2008), p. 324.
- Robert Foley, "The Evolutionary Consequences of Increased Carnivory in Hominids", in Meat-Eating and Human Evolution (2001), p. 321.
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