A plant-based diet is a diet consisting mostly or entirely of foods derived from plants, including vegetables, grains, nuts, seeds, legumes and fruits, and with few or no animal products. Historically, it was explained that "[a] plant-based diet is not necessarily a vegetarian diet", as "[m]any people on plant-based diets continue to use meat products and/or fish but in smaller quantities". The use of the phrase plant-based 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. The Academy of Nutrition and Dietetics issued a position statement proposing that well-planned plant diets support health and are appropriate throughout life, including pregnancy, lactation, childhood, adulthood, and for athletes.
A 2017 review of clinical research on the dietary patterns of people with type 2 diabetes stated that the kinds of carbohydrates (unrefined versus refined), fats (monounsaturated and polyunsaturated versus saturated and trans), and protein (plant versus animal) in a plant-based diet have significant roles in lowering the risk and managing diabetes and other diseases, such as cardiovascular disorders, obesity, and cancer.
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 tended to equate a plant-based diet with veganism, although at points the book describes people having a "mostly" whole-food plant-based diet. Vegan author 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.
Several sources use 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:
- Veganism: diet of vegetables, legumes, fruit, grains, nuts, and seeds, but no food from animal sources.
- Vegetarianism: diet of vegetables, legumes, fruit, nuts, and grains, that may include eggs and dairy, but no meat.
- Semi-vegetarianism: mostly vegetarian diet with occasional inclusion of meat and/or poultry.
- Macrobiotic diet: semi-vegetarian diet that highlights whole grains, vegetables, beans, miso soup, sea vegetables, and traditionally or naturally processed foods, with or without seafood and other animal products.
- Pescatarian: semi-vegetarian diet with eggs, dairy and seafood.
- Flexitarian: semi-vegetarian diet that includes limiting meat intake daily and/or being vegetarian only on certain days of the week.
Some reviews indicated that a plant-based diet might lower the risk of diabetes, cancer, and cardiovascular diseases by reducing total and LDL cholesterol. 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.
Modern herbivores and mild omnivoryEdit
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.
The Food and Agriculture Organization defined a sustainable diet as one with ‘low environmental impacts which contribute to food and nutrition security, and to healthy life for present and future generations’, and one that is affordable for all while optimizing both natural and human resources. A sustainable diet can be measured by its level of nutritional adequacy, environmental sustainability, cultural acceptability and affordability.
Environmental sustainability can be measured by indicators of efficiency and environmental protection. Efficiency measures the ratio of inputs and outputs required to produce a given level of foods. Input energy refers to processing, transporting, storing and serving food, compared with the output of physical human energy. Conversely, environmental protection refers to the level of preservation of ecological systems.
Plant-based diets may contribute to reducing greenhouse gas emissions and the amount of land, water and fertilizers used for agriculture. As a significant percentage of crops around the world are used to feed livestock rather than humans, increasing the practice of a plant-based diet may contribute toward minimizing climate change and biodiversity loss. While "soy cultivation is a major driver of deforestation in the Amazon basin", most soy crops are not destined for human consumption.
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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.
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... 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.
- McManus, Katherine D. (September 26, 2018). "What is a plant-based diet and why should you try it?". Harvard Medical School.
It doesn't mean that you are vegetarian or vegan and never eat meat or dairy. Rather, you are proportionately choosing more of your foods from plant sources.
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Worldwide, an estimated 2 billion people live primarily on a meat-based diet, while an estimated 4 billion live primarily on a plant-based diet. The shortages of cropland, fresh water, and energy resources require most of the 4 billion people to live on a plant-based diet
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meat and dairy provide only 18% of our calories and 37% of our protein, yet use up 83% of our farmland.