Potential Nutrition of Vegetarian

Vegetarian diets can be relatively low in protein, iron, zinc, vitamin B12, calcium, omega-3 fatty acids, retinol (vitamin A), vitamin D, riboflavin (vitamin B2) and iodine. Poorly planned vegetarian diets may sometimes fall short in vitamin B12, calcium, omega-3 fatty acids, vitamin D, iron and zinc, and some vegans may have particularly low intakes of vitamin B12 and calcium. Nonetheless, well-balanced vegetarian and vegan diets can meet all these nutrient requirements and are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence.


Protein

The typical vegetarian gets adequate protein as long as caloric intake is adequate and a variety of foods is eaten. Vegetarian diets are usually relatively low in protein, which may be beneficial
Despite a widespread belief that vegetarians must eat grains and beans within a few hours of each other in order to make a 'complete' protein which contains all 9 "essential amino acids", this has never been substantiated by research. The protein-combining theory was brought to popular attention in Frances Moore Lappé's 1971 bestseller Diet for a Small Planet. In later editions of the book, as early as 1981, Lappé withdrew her contention that protein 'combining' is necessary.

Iron

In several studies, vegans and other vegetarians were not found to suffer from iron-deficiency more than non-vegetarians. However, while one study agreed that iron-deficiency anemia is not more common among vegetarians, they found "vegetarian children had ... reduced levels of haemoglobin and iron compared to omnivores" due "to the absence of animal iron sources with high utilizability".
Tofu can be a valuable source of protein, iron, zinc and calcium for vegetarians and vegans
The recommended iron intake for vegetarians is 1.8 times that of nonvegetarians, due to the fact that plants, dairy, and eggs contain only non-heme iron, and this is absorbed less efficiently than heme iron. Although a lower percentage of non-heme iron is absorbed, greater amounts of non-heme iron are concentrated in many non-meat sources of iron (than the amount of iron per serving in meats), and therefore, cereals, eggs, nuts, seeds, and legumes (including soy foods, peas, beans, chickpeas, and lentils) are significant sources of iron, and a well-planned vegetarian diet should not lead to iron deficiency, but fruitarianism and raw foods diets should not be pursued for infants or children. Meat, fish, and poultry (not dairy or eggs) are the only sources of heme iron; intake of heme iron is associated with colon cancer. Non-heme iron is more sensitive to both inhibitors and enhancers of iron absorption. Vitamin C is an iron absorption enhancer. The main inhibitors for most people are phytates (e.g. legumes and grains), but other inhibitors include tannins (tea, wine), calcium and polyphenols.
Iron is an integral part of many proteins and enzymes which maintain good health. In humans, iron is an essential component of proteins involved in red blood cells' oxygen transport. Iron also helps regulate cell growth and differentiation.

Zinc

Western vegetarians and vegans have not been found to suffer from overt zinc deficiencies any more than meat-eaters. However, phytates in many whole-grains and fiber in many foods may interfere with zinc absorption and marginal zinc intake has poorly understood effects. Vegetarians may need more than the US RDA (15 mg) of zinc daily if their diet is high in phytates.
Major plant sources of zinc include cooked dried beans, sea vegetables, fortified cereals, soyfoods, nuts, peas, and seeds.

Vitamin B12

Eggs are an excellent source of vitamin B12 for vegetarians.
Vitamin B12 deficiency is potentially extremely serious, leading to pernicious anemia, nerve degeneration and irreversible neurological damage.
Lacto-ovo vegetarians may get vitamin B12 from eggs and dairy products; for some this is adequate but some may remain B12-deficient. The world's largest group of professional dietitians says the form of vitamin B12 sourced from animal-products is protein-bound and not as easily digested, especially as people age, and therefore recommends B12 supplementation for everyone over the age of 50. Pregnant and lactating vegetarians (and breastfed infants if the mother's diet is not supplemented) should also use supplements, whether pills, injections, or B12-fortified foods, if they don't get adequate B12 from animal-products like eggs or dairy.
Evidence suggests that vegetarians and vegans who are not taking vitamin B12 supplements do not consume sufficient servings of B12 and often have abnormally low blood concentrations of vitamin B12. This is because, unless fortified, plant foods do not contain reliable amounts of active vitamin B12.
It is essential, therefore, that vegetarians consume adequate amounts of dietary supplements or foods that have been fortified with B12 (such as nutritional yeast or other yeast extracts, vegetable stock, veggie burger mixes, textured vegetable protein, soy milks, vegetable and sunflower margarines, and breakfast cereals). B12 that is to be used in these supplements is typically grown from vegan sources (such as bacteria). Another bacterial source happens to be that plants and edible fungi (like mushrooms) on farms or in the wild may absorb vitamin B12 from bacteria in soil, but since modern pesticides kill most B12 in the soil (including on organic farms to some degree, as the pesticides spread, via hydrology, from non-organic farms to organic ones), the B12 in these plants is not considered a reliable dietary source, whereas B12 supplements from bacteria grown under controlled conditions are considered reliable amounts of B12. There is a patent for a cultivating vitamin B12 from plants.
Nori (seaweed) contains B12 very abundantly. However, while the one included in Nori is effectiveit does not contain reliable or significant amounts of active B12; instead, seaweeds tend to be high in inactive B12 which actually may inhibit uptake of active B12.

Omega-3 fatty acids

Vegetarian diets that lack eggs or generous amounts of sea vegetables (seaweed) can be low in omega-3 fatty acids (O3FA). This and a high ratio of O6FA to O3FA in the diet may raise risk of heart disease in some vegetarians. Major vegetarian sources of O3FA include walnuts, flaxseeds and flaxseed oil, olive oil, canola (rapeseed) oil, and avocado. DHA supplements derived from DHA-rich microalgae are also available.
Common flax seed contains more omega-3 fatty acids than fish.

Walnuts are a source of omega-3 fatty acids
A well-known source of O3FA for non-vegetarians is fish, and to get the same amount of O3FA, one needs to only consume 1/3 the weight of walnuts compared to a given weight of salmon; and flax seeds have even more highly-concentrated O3FA than walnuts. However, vegetarian sources of O3FA are primarily the short chain variety and likely to have lower concentrations of the particular essential fatty acids (EFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The body can synthesize small quantities of EPA and DHA from other omega-3 fatty acids, such as alpha-linolenic acids, which are present in vegetarian sources of O3FA's. The human body can also convert DHA into EPA. Whilst the human body can in theory do this conversion, in practice modern diets and lifestyles reduce the effectiveness of the conversion systems.[citation needed] Roughly ten times[citation needed] more of the short chain omega-3s must be consumed to have the same effect as the long chain form from fish oil.
While there is no scientific consensus on the role of omega-3 fatty acids, it is generally believed that they may reduce the risk of coronary heart disease, lower triglycerides, stabilize mood and help prevent depression, help reduce symptoms of ADD, reduce joint pain and other rheumatoid problems and reduce the risk of dementia in older age.

Vitamin D

The human body can synthesize vitamin D when skin is exposed to ultraviolet radiation from the sun. Vegans who do not eat foods or pills fortified with synthetic vitamin D and with little exposure to the sun's ultraviolet radiation (e.g., those who don't expose their extremities for at least 15-30 minutes per day or those living at latitudes close to the poles) are vulnerable to Vitamin D deficiencies.
Vitamin D acts as a hormone, sending a message to the intestines to increase the absorption of calcium and phosphorus, which produces strong bones. Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization. Research also suggests that vitamin D may help maintain a healthy immune system and help regulate cell growth and differentiation.


Iodine


One study reported a "potential danger of [iodine] deficiency disorders due to strict forms of vegetarian nutrition, especially when fruits and vegetables grown in soils with low [iodine] levels are ingested." Iodine, however, is usually supplied by iodized salt and other sources in first world countries. Other significant sources of iodine include sea vegetables (seaweed) and bread made with dough conditioners.

Riboflavin

According to the American Dietetic Association, “Some studies have shown vegans to have lower intakes of riboflavin, compared with nonvegetarians; however, clinical riboflavin deficiency has not been observed.”