Protein Despite the long-standing, widespread belief that vegetarians must consume grains and beans within a short time to make a
complete protein that contains all 9
essential amino acids that must be supplied through diet, this has never been substantiated by research. The protein-combining theory was brought to popular attention after being promoted in
Frances Moore Lappé's 1971 bestselling book
Diet for a Small Planet. In later editions of the book, starting in 1981, Lappé withdrew her contention that
protein combining is necessary. Plant foods rich in protein include
soy beans and soy products such as
tofu,
veggie burgers, and
soy milk; other
legumes;
nuts and
seeds; and
cereal grains.
Vitamin B12 Vitamin B12 deficiency can be extremely serious and lead to
megaloblastic anemia, nerve degeneration and irreversible neurological damage. There are cases to suggest that vegetarians and vegans who are not taking vitamin B12 supplements or food fortified with B12 do not consume sufficient servings of B12 and have abnormally low blood concentrations of vitamin B12. This is because, unless fortified, plant foods do not contain reliable amounts of active
vitamin B12. B12 used in these foods or supplements is typically grown from vegan sources (such as
bacteria). Soybeans and barley seeds from plants grown in soils amended either with cow dung (which is rich in B12) or with pure B12 had a higher B12 content than those grown without this supplementation.
Omega-3 fatty acids s are a rich source of ALA, but contains negligible amounts of DHA and EPA, the
long-chain omega-3 fatty acids the FDA considers to be healthful. Vegetarian diets can be low in
omega-3 fatty acids (O3FAs). Major vegetarian O3FA sources include
algae,
hempseeds and hempseed oil,
walnuts,
flaxseeds and flaxseed oil,
olive oil,
canola oil,
avocado, and
chia seeds. A potential problem is that vegetarian diets lacking eggs or generous amounts of
edible seaweed generally lack a direct source of
long-chain O3FAs such as
docosahexaenoic acid (DHA) and
eicosapentaenoic acid (EPA). Vegetarian diets may also have a high ratio of
omega-6 fatty acids to O3FAs, which inhibits the conversion of short-chain fatty acids such as
alpha-Linolenic acid (ALA), which is found in most vegetarian O3FA sources, to EPA and DHA. To remedy this, DHA and EPA supplements derived from microalgae are available. A 2022 review found that
microalgal oil supplementation is consistent in increasing DHA and EPA levels, whilst high dose
flaxseed or
echium seed oil supplements provide no increase despite significant increases in ALA levels. A 2022 review found no significant difference in calcium intake between vegetarians and omnivores. Vegetarians can obtain calcium from
dairy products, calcium-fortified
plant milks, almonds, figs, oranges, calcium-set tofu as well as low-oxalate vegetables such as bok choy, kale and turnip greens.
Iron Vegetarians are more likely to have lower iron stores compared with non-vegetarians and have a higher risk of iron deficiency anemia. Lacto-ovo-vegetarians that overly rely on dairy consumption may lead to an elevated calcium intake which can affect iron absorption. , a soy product, can be a valuable source of not only iron, but also protein, zinc and calcium for vegetarians. The recommended iron intake for vegetarians is 180% that of nonvegetarians due to the bioavailability of non-heme iron. 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
cereal grains), but other inhibitors include
tannins (from
tea and
wine),
calcium, and
polyphenols.
Zinc A 2013 review found that zinc intake and serum zinc concentrations were significantly lower in populations that follow vegetarian diets compared with non-vegetarians.
Phytates in many
whole grains, and
dietary fiber in many plant foods may interfere with zinc absorption, and marginal zinc intake has poorly understood effects. Vegetarians may need more than the US
Recommended Daily Allowance of 15 mg of zinc each day to compensate if their diet is high in phytates. Iodine, however, is usually supplied by
iodized salt and other sources in
first world countries. Other significant vegetarian sources of iodine include
edible seaweed and bread made with
dough conditioners. ==Health effects==