VEGAN nutrition

If you are a Vegan, you must choose very wisely your meal ingredients, in order to meet all your body needs for nutrients

                                

Vitamin B12

Vitamin B12  is a bacterial product needed for cell division, the formation and maturation of red blood cells, the synthesis of DNA, and for normal nerve function. A B12 deficiency can lead to a number of health problems, including megaloblastic anemia and nerve damage. That vegans are unable in most cases, at least in the West, to obtain vitamin B12 from a plant-based diet without consuming fortified foods or supplements is often used as an argument against veganism.

Neither plants nor animals make B12; it is produced by microorganisms, such as bacteria, fungi and algae. Herbivorous animals obtain it from bacteria in their rumens, either by absorbing it or by eating their own cecotrope faeces; rabbits, for example, produce and eat cecal pellets. When those animals are eaten, they become sources of B12. Plants from the ground that are not washed properly may contain B12 from bacteria in the soil, often from faeces; drinking water may also be contaminated with B12-producing bacteria, particularly in the developing world. Reed Mangelsof the department of nutrition at the University of Massachusetts Amherst writes that bacteria in the human digestive tract produce B12, but most of it is not absorbed and is expelled in the faeces, with tiny amounts also expelled in the urine. James Halsted, a medical researcher, reported in the 1960s that a group of villagers in Iran eating very little or no animal protein were found to have normal B12 levels because they were living with animal manure near their homes, and were eating vegetables grown in human manure (known as night soil) and not thoroughly washed. The human mouth is another source of B12, but in small amounts and possibly analogue (not biologically active).

Western vegan diets are likely to be deficient in B12 because of increased hygiene. Vegans can obtain B12 by taking a supplement or by eating fortified foods, such as fortified soy milk or cereal, where it may be listed as cobalamin or cyanocobalamin. B12 supplements are produced industrially through bacterial fermentation-synthesis; no animal products are involved in that process.

There is some disagreement within the vegan community as to whether supplementation is needed; several studies of vegans who did not take supplements or eat fortified food, including in Western countries, have found no sign of B12 deficiency. Mangels writes that the disagreement is caused in part because there is no gold standard for assessing B12 status, and also because there are very few studies of long-term vegans who have not used supplements or fortified foods. According to Mangels, all Western vegans not using supplements or fortified foods will probably develop a B12 deficiency, though it may take decades to appear. There are reports that certain plant foods are sources of B12. Mangels writes that fermented foods such as tempeh and miso, as well as edible seaweed (such as arame, wakame, nori, and kombo), spirulina, and certain greens, grains and legumes, have been cited as B12 sources, as has rainwater. She writes that tiny amounts have been found in barley malt syrup, shiitake mushrooms, parsley and sourdough bread, and higher amounts in spirulina and nori, but these products may be sources of inactive B12. The consensus within the mainstream nutrition community is that vegans and perhaps even vegetarians should eat fortified foods or use supplements.

Proteins

Proteins are composed of amino acids. Mangels et al write that omnivores generally obtain a third of their protein from plant foods, and ovo-lacto vegetarians a half. Vegans obtain all their protein from plant sources, and a common concern is whether plant protein supplies an adequate intake of the essential amino acids, which cannot be synthesized by the human body. 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.

Soybeans and quinoa (pronounced keenwa) both have high protein contents and are known as complete proteins because they each contain all the essential amino acids. Other common combinations that contain all the essential amino acids are rice and beans, corn and beans, and hummus and whole-wheat pita; a 1994 study found a varied intake of such sources to be sufficient. Mangels et al write that there is little reason to advise vegans to increase their protein intake, but erring on the side of caution (taking into account the lower digestibility and poorer amino acid pattern of plant protein), they would recommend a 25 percent increase over the RDA for adults, to 1.0 gram of protein per kilogram of body weight. According to a 2005 review article, studies suggest that an adequate intake of plant proteins protects against certain degenerative diseases.

  

Calcium

Calcium is needed to maintain bone health, and for a number of metabolic functions, including muscle function, vascular contraction and vasodilation, nerve transmission, intracellular signalling and hormonal secretion. Ninety-nine percent of the body's calcium is stored in the bones and teeth. Vegans are advised to eat three servings per day of a high-calcium food, such as fortified soy milk, fortified tofu, almonds or hazelnuts, and to take a supplement as necessary. Plant sources include Chinese cabbage (bok choi), kale, broccoli and turnip; the bioavailability of calcium in spinach is poor. Whole wheat bread contains calcium; grains contain small amounts. Because vitamin D is needed for calcium absorption, vegans should make sure they consume enough vitamin D too (see below).

The EPIC-Oxford study suggested that vegans have an increased risk of bone fractures over meat eaters and vegetarians, likely because of lower dietary calcium intake, but that vegans consuming more than 525 mg/day have a risk of fractures similar to that of other groups.  A 2009 study of bone density found the bone mineral density (BMD) of vegans was 94 percent that of omnivores, but deemed the difference clinically insignificant. Another study in 2009 by the same researchers examined over 100 vegan post-menopausal women, and found that their diet had no adverse effect on BMD and no alteration in body composition. Biochemist T. Colin Campbell suggested in The China Study (2005) that osteoporosis is linked to the consumption of animal protein; he argued that, unlike plant protein, animal protein increases the acidity of blood and tissues, which is then neutralized by calcium pulled from the bones.

Vitamin D 

Vitamin D (calciferol) is needed for a number of functions, including calcium absorption, enabling mineralization of bone, and bone growth. Without it bones can become thin and brittle; together with calcium it offers protection against osteoporosis. Mangels writes that it may also play a role in protecting against heart disease, diabetes, colon cancer, multiple sclerosis and dementia. Vitamin D is produced in the body when ultraviolet rays from the sun hit the skin; outdoor exposure is needed because UVB radiation does not penetrate glass. It is present in very few foods (mostly salmon, tuna, mackerel, cod liver oil, with small amounts in cheese, egg yolks and beef liver, and in some mushrooms).

Most vegan diets contain little or no vitamin D, unless the food is fortified (such as fortified soy milk), so supplements may be needed depending on exposure to sunlight. Vitamin D comes in two forms. Cholecalciferol (D3) is synthesized in the skin after exposure to the sun and may be consumed in the form of animal products; when produced industrially it is taken from lanolin in sheep's wool. Ergocalciferol(D2) is suitable for vegans; it is mostly human-made and is derived from ergosterol from yeast. Several conflicting studies have suggested that the two forms may or may not be bioequivalent. According to a 2011 report by the Food and Nutrition Board of the National Academy of Sciences, the differences between D2 and D3 do not affect metabolism, both function as prohormones, and when activated exhibit identical responses in the body.

Supplements should be used with caution because vitamin D can be toxic, especially in children.

The extent to which sun exposure is sufficient to meet the body's needs will depend on the time of day, cloud and smog cover, skin melanin content, whether sunscreen is worn, and the season. According to the US National Institutes of Health, most people can obtain and store sufficient vitamin D from sunlight in the spring, summer and fall months, even in the far north. They report that some vitamin D researchers recommend 5–30 minutes of sun exposure without sunscreen between ten in the morning and three o'clock in the afternoon, at least twice a week. They also report that tanning beds emitting two to six per cent UVB radiation will have a similar effect, though using tanning beds may be inadvisable for other reasons.

Iron 

Vegetarian and vegan diets usually contain as much iron as animal-based diets, or more; vegan diets generally contain more iron than vegetarian ones because dairy products contain very little. There are concerns about the bioavailability of iron from plant foods, assumed by some researchers to be around 5–15 percent compared to 18 percent from a nonvegetarian diet. Iron deficiency anaemia is found as often in nonvegetarians as in vegetarians, though studies have shown vegetarians' iron stores to be lower.

Mangels writes that because of the lower bioavailability of iron from plant sources, the Food and Nutrition Board of the National Academy of Sciences established a separate RDA for vegetarians and vegans of 14mg for vegetarian men and postmenopausal women, and 33 mg for premenopausal women not using oral contraceptives. Supplements should be used only with caution after consulting a physician, because iron can accumulate within the body and cause damage to organs; this is particularly true of anyone suffering from hemochromatosis, a relatively common condition that can remain undiagnosed. The tolerable upper intake level (daily), according to the National Institutes of Health, is 40 mg for 7 months to 13 years, and 45 mg for 14+.

According to the Vegetarian Resource Groups, high-iron foods suitable for vegans include black-strap molasses, lentils, tofu, quinoa, kidney beans and chickpeas. Tom Sanders, a nutritionist at King's College London, writes that iron absorption can be enhanced by eating a source of vitamin C along with a plant source of iron, and by avoiding coingesting anything that would inhibit absorption, such as tannin in tea. Sources of vitamin C might be half a cup of cauliflower, or five fluid ounces of orange juice, consumed with a plant source of iron such as soybeans, tofu, tempeh, or black beans. Some herbal teas and coffee can also inhibit iron absorption, as can spices that contain tannins (turmeric, coriander, chillies, and tamarind).

Alpha-linolenic acid (ALA), an omega-3 fatty acid, is found in leafy green vegetables and nuts, and in vegetable oils such as canola and flaxseed oil. The Adequate Intake for ALA is 1.1–1.6 g/day. Vegan Outreach suggests vegans take 1/4 teaspoon of flaxseed oil (also known as linseed oil) daily, and use oils containing low amounts of omega-6 fatty acids, such as olive, canola, avocado or peanut oil.

Iodine supplementation may be necessary for vegans in countries where salt is not typically iodized, where it is iodized at low levels, or where, as in Britain and Ireland, dairy products are relied upon for iodine delivery because of low levels in the soil. Iodine can be obtained from most vegan multivitamins or from regular consumption of seaweeds, such as kelp.

Pregnancy, babies and children

The American Dietetic Association and Dietitians of Canada consider well-planned vegan diets "appropriate       for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood and adolescence."

The Swiss Federal Nutrition Commission and the German Society for Nutrition caution against a vegan diet for pregnant women and children. A doctor or registered dietitian should be consulted about taking supplements during pregnancy. The American Dietetic Association write that a regular source of B12 is crucial for pregnant, lactating and breastfeeding women. According to Reed Mangels, maternal stores of B12 appear not to cross the placenta, and researchers have reported cases of vitamin B12 deficiency in lactating vegetarian mothers that were linked to deficiencies and neurological disorders in their children. Pregnant vegans may also need to take extra vitamin D, depending on their exposure to sunlight and whether they are eating fortified foods. Doctors may recommend iron supplements and folic acid for all pregnant women (vegan, vegetarian and non-vegetarian).

Newspapers have reported several cases of malnutrition in children whose parents said they were vegan. A 12-year-old girl in Scotland who had eaten no meat or dairy since birth was found in 2008 to be suffering from rickets (caused by a lack of vitamin D), and had several fractures. In 2000 in London, a nine-month-old girl died after her vegan mother fed her a fruitarian diet of raw fruit and nuts. In 2004 in Atlanta, a six-week-old boy died after his vegan parents appear to have fed him mostly apple juice and soy milk. The prosecution argued that the case was not about veganism, but that the child had simply not been fed. Dr. Amy Lanou, nutrition director of the Physicians Committee for Responsible Medicine, and an expert witness for the prosecution in that case, argued that vegan diets are "not only safe for babies; they're healthier than ones based on animal products," and wrote that "the real problem was that [the child] was not given enough food of any sort."

Text source: www.wikipedia.com