The Vegan Diet
The main difference between a vegan and vegetarian diet is that vegans exclude eggs and dairy products. Ethical vegans avoid them on the premise that their production causes animal suffering and premature death. In egg production, most male chicks are culled because they do not lay eggs. To obtain milk from dairy cattle, cows are made pregnant to induce lactation; they are kept pregnant and lactating for three to seven years, then slaughtered. Female calves are separated from their mothers within 24 hours of birth, and fed milk replacer to retain the cow's milk for human consumption. Male calves are slaughtered at birth, sent for veal production, or reared for beef.
Vegan groups disagree about insect products. Neither the Vegan Society nor the American Vegan Society considers honey, silk, and other insect products as suitable for vegans, while Vegan Action and Vegan Outreach view it as a matter of personal choice. Agave nectar is a popular vegan alternative to honey.
Vegan diets are based on grains and other seeds, legumes (particularly beans), fruits, vegetables, edible mushrooms, and nuts. Meat analogues (mock meats) based on soybeans (tofu), or wheat-based seitan/gluten, are a common source of plant protein, usually in the form of vegetarian sausage, mince, and veggie burgers.
Dishes based on soybeans are a staple of vegan diets because soybeans are a complete protein; this means they contain all the essential amino acids for humans and can be relied upon entirely for protein intake. They are consumed most often in the form of soy milk and tofu (bean curd), which is soy milk mixed with a coagulant. Tofu comes in a variety of textures, depending on water content, from firm, medium firm, and extra firm for stews and stir-fries; to soft or silken for salad dressings, desserts, and shakes. Soy is also eaten in the form of tempeh and texturized vegetable protein (TVP); also known as textured soy protein (TSP), the latter is often used in pasta sauces.
Plant milks—such as soy milk, almond milk, grain milks (oat milk and rice milk), hemp milk, and coconut milk—are used in place of cows' or goats' milk. Soy milk provides around 7 g of protein per cup (240 mL or 8 fl oz), compared with 8 g of protein per cup of cow's milk. Almond milk is lower in dietary energy, carbohydrates and protein.
Butter can be replaced with a vegan alternative such as Earth Balance's. Vegan (egg-free) mayonnaise brands include Vegenaise, Nayonaise, Miso Mayo, Just Mayo, Mindful Mayo, and Plamil's Egg-Free Mayo.
Vegan cheeses such as Chreese, Daiya, Sheese, Teese, Violife, Follow your heart and Tofutti, are made from soy, nuts and tapioca, and can replace the meltability of dairy cheese.Nutritional yeast is a common substitute for the taste of cheese in vegan recipes. Several recipe books describe how to make cheese substitutes at home;one recipe for vegan brie combines cashew nuts, soy yogurt and coconut oil. In 2014 Oakland's Counter Culture Labs and Sunnyvale's BioCurious produced vegan cheese from casein extracted from genetically modified yeast.
Since 1991 the Physicians Committee for Responsible Medicine (PCRM) has recommended a no-cholesterol, low-fat vegan diet based on what they call the New Four Food Groups: fruit, legumes, grains and vegetables. Legumes include peas, beans, lentils and peanuts.
PCRM recommends three or more servings a day of fruit (at least one of which is high in vitamin C, such as citrus fruit, melon or strawberries); two or more of protein-rich legumes (such as soybeans, which can be consumed as soy milk, tofu or tempeh); five or more of whole grains(such as corn, barley, rice and wheat, in products such as bread and tortillas); and four or more of vegetables (dark-green leafy vegetables such as broccoli, and dark-yellow and orange such as carrots or sweet potatoes).
The New Four Food Groups was created as an alternative to the Four Food Groups – meat, milk, vegetables and fruit, and cereal and breads – recommended by the United States Department of Agriculture (USDA) from 1956 until 1992. In 1992 the USDA replaced this with the food guide pyramid and in 2011 with MyPlate, which is consistent with a vegan diet. MyPlate is divided into five groups: grains, vegetables, fruits, dairy products (or calcium-fortified soymilk), and protein. The protein includes meat, poultry, seafood, beans and peas, eggs, processed soy products, nuts and seeds. In the UK the National Health Service recommends the Eatwell Plate, also with five groups and consistent with a vegan diet: fruit and vegetables; potatoes, bread and other starchy foods; dairy products or non-dairy alternatives; meat, fish, eggs, or beans for protein; and fat and sugar.
Vegans obtain all their protein from plants, omnivores usually a third, and ovo-lacto vegetarians half. Sources of plant protein include legumes such as soy beans (consumed as tofu, tempeh, texturized vegetable protein, soy milk and edamame), peas, peanuts, black beans and chickpeas (the latter often eaten as hummus); grains such as quinoa (pronounced keenwa), brown rice, corn, barley, bulgur and wheat (the latter eaten as bread and seitan); and nuts and seeds. Combinations that contain high amounts of all the essential amino acids include rice and beans, corn and beans, and hummus and whole-wheat pita.
Soy beans and quinoa are known as complete proteins because they each contain all the essential amino acids in amounts that meet or exceed human requirements, although analyses disagree on whether soy protein is slightly deficient in the sulfur-containing amino acids methionineand cystine, leading to reported PDCAAS values between 0.92 (slightly incomplete) and 1.00 (truly complete). Mangels et al. write that consuming the recommended dietary allowance (RDA) of protein (0.8 g/kg body weight) in the form of soy will meet the biologic requirement for amino acids. In 2012 the United States Department of Agriculture ruled that soy protein (tofu) may replace meat protein in the National School Lunch Program.
The American Dietetic Association said in 2009 that a variety of plant foods consumed over the course of a day can provide all the essential amino acids for healthy adults, which means that protein combining in the same meal may not be necessary. Mangels et al. write that there is little reason to advise vegans to increase their protein intake, but erring on the side of caution, they recommend a 25% increase over the RDA for adults, to 1.0 gram of protein per kilogram of body weight.
Vitamin B12 is a bacterial product needed for cell division, the formation and maturation of red blood cells, the synthesis of DNA, and normal nervefunction. A deficiency can lead to megaloblastic anaemia and nerve damage. Vegans are unable in most cases to obtain B12 from their diet. Vegetarians are also at risk, as are older people and those with certain medical conditions. A 2013 study found that "vegetarians develop B12 depletion or deficiency regardless of demographic characteristics, place of residency, age, or type of vegetarian diet. Vegetarians should thus take preventive measures to ensure adequate intake of this vitamin, including regular consumption of supplements containing B12."
Increased hygiene in the food supply is probably the cause of B12 depletion from plant-based diets. Neither plants nor animals make B12; it is produced by microorganisms, such as bacteria, fungi, and algae. Plants not washed properly may contain B12 from bacteria in the soil, often from faeces, and drinking water may be similarly contaminated, particularly in the developing world. Animals obtain it by eating contaminated plants, from their internal bacteria, other animals, or their own faeces, and become sources of B12 if eaten themselves. Intensively farmed animals are often given B12 supplements or injections, particularly pigs and poultry, because when raised indoors they have no access to plants and less access to their own faeces. Bacteria in the human digestive tract produce B12, but most is expelled in the faeces. The mouth is another source, but in small amounts and possibly analogue (not biologically active).
Japanese researchers say that around 4 g of dried purple nori, an edible seaweed, supplies the adult RDA of 2.4 micrograms (µg) of B12. Tempeh, a fermented soybean food, is cited as another source, perhaps because of contamination during production. One tablespoon of Red StarVegetarian Support Formula nutritional yeast delivers the adult RDA of B12. There is no gold standard for assessing B12 status and few studies exist of long-term vegans who have not used supplements or fortified foods. Studies of vegans not taking supplements or eating fortified food have found low B12 levels and clinical signs of deficiency; low B12 levels without signs of a deficiency; and neither. Nevertheless, the consensus among researchers is that vegans and vegetarians should use supplements, or eat B12-fortified foods such as plant milk or breakfast cereal. Mangels et al. say: "It is likely that all Western vegans consuming unsupplemented diets will eventually develop vitamin B12 deficiency, although it may take decades for this to occur." No animal products are involved in the production of B12 supplements.
Calcium is needed to maintain bone health and for several metabolic functions, including muscle function, vascular contraction and vasodilation, nerve transmission, intracellular signalling and hormonal secretion. 99% of the body's calcium is stored in the bones and teeth.
Vegans are advised to eat three servings a day of a high-calcium food, such as fortified plant milk, fortified tofu, almonds or hazelnuts, and to take a supplement as necessary. Plant sources include broccoli, turnip, bok choy and kale; the bioavailability of calcium in spinach is poor. Vegans should make sure they consume enough vitamin D, which is needed for calcium absorption.
A 2007 report based on the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition, which began in 1993, suggested that vegans have an increased risk of bone fractures over meat eaters and vegetarians, likely because of lower dietary calcium intake. The study found that vegans consuming at least 525 mg of calcium daily have a risk of fractures similar to that of other groups. A 2009 study found the bone mineral density (BMD) of vegans was 94% that of omnivores, but deemed the difference clinically insignificant.
Most vegan diets contain little or no vitamin D without fortified food. People with little sun exposure may need supplements. The extent to which sun exposure is sufficient depends on the season, time of day, cloud and smog cover, skin melanin content, and whether sunscreen is worn. According to the National Institutes of Health, most people can obtain and store sufficient vitamin D from sunlight in the spring, summer and fall, even in the far north. They report that some researchers recommend 5–30 minutes of sun exposure without sunscreen between 10 am and 3 pm, at least twice a week.
Vitamin D comes in two forms. Cholecalciferol (D3) is synthesized in the skin after exposure to the sun, or consumed in the form of animal products; when produced industrially it is taken from lanolin in sheep's wool. Ergocalciferol (D2) is derived from ergosterol from UV-exposed mushrooms or yeast and is suitable for vegans. Conflicting studies have suggested that the two forms may or may not be bio-equivalent. According to researchers from the Institute of Medicine, the differences between D2 and D3 do not affect metabolism, both function as prohormones, and when activated exhibit identical responses in the body.