Vegetarian Diet
Manual of Clinical Nutrition Management A- 38 Copyright © 2013 Compass Group, Inc.
Vitamin D: Vitamin D status depends on sunlight exposure and intake of vitamin D–fortified foods or
supplements (1). If sun exposure and intake of fortified foods are insufficient to meet nutritional needs, vitamin D
supplements are recommended (1). Vitamin D 3 (cholecalciferol) is of animal origin and may not be used by
vegans. Vitamin D 2 (ergocalciferol) is produced from ergosterol from yeast and is a form that may be more
frequently used by vegans. There is disparity in the research as to whether the bioavailability of vitamin D 2 is
less than that of vitamin D 3 (1,16). The need for additional requirements when vitamin D 2 sources are primarily
used is not currently suggested by the evidence (1,16). Both vitamin D 2 and vitamin D 3 are used in supplements
and to fortify foods (1). Because cutaneous vitamin D production decreases with aging process, dietary or
supplemental sources of vitamin D are important when assessing the diets of older adults (1,17).
Energy: Because vegan diets tend to be high in bulk, it can be challenging for vegans, especially infants, children,
and adolescents, to meet their energy needs. Frequent meals and snacks and the use of some refined foods (such
as fortified breakfast cereals, breads, and pasta) and foods higher in unsaturated fats can help vegan children
meet their energy and nutrient needs (1).
Iron: The non-heme iron found in plant foods is more sensitive than heme iron to both inhibitors and enhancers
of iron absorption (1). The inhibitors of iron absorption include phytate, calcium, and polyphenols in teas
(including some herb teas), coffee, and cocoa (1). Fiber only slightly inhibits iron absorption (1,18). Some food
preparation techniques, such as soaking and sprouting beans, grains, and seeds and the leavening of bread, can
diminish phytate levels and thereby enhance iron absorption (1). Western vegetarians have a relatively high
intake of iron from plant foods, such as dark-green leafy vegetables, iron-fortified cereals, and whole grains.
Although vegetarian diets are higher in total iron than nonvegetarian diets, iron stores are lower because iron
from plant foods is not absorbed as well as iron from animal sources (1). Because of the lower bioavailability of
iron from a vegetarian diet, the recommended iron intakes for vegetarians are 1.8 times those of nonvegetarians
(1,19). However, the frequency of anemia is not higher in the vegetarian population than in the nonvegetarian
population (1). There is evidence of long-term adaptation to low iron intakes that involves both increased
absorption and decreased losses (1,20,21). In addition, vitamin C and other organic acids in fruits and vegetables
consumed by vegetarians can substantially enhance iron absorption and reduce the inhibitory effects of phytates,
leading to improved iron status (1).
Zinc: Because phytate binds zinc, and animal protein is believed to enhance zinc absorption, total zinc
bioavailability appears to be lower in vegetarian diets (1,22). Vegetarians, especially those who consume phytate-
rich unrefined grains and legumes, should strive to meet or exceed the DRIs for zinc due to the low bioavailability
of zinc from plant sources and the high phytate content of a vegetarian diet (1,19). In addition, breast-fed infants
should have their diets evaluated for zinc intake. Zinc-fortified foods or supplements should be used when
complementary foods are introduced, if the diet is low in zinc or mainly consists of foods with low zinc
availability (1). Due to difficulty in evaluating zinc deficiency, it is not possible to determine the possible effect of
lower zinc absorption from vegetarian diets (22). Zinc sources include soy products, legumes, grains, cheese, and
nuts. Food preparation techniques, such as the soaking and sprouting of beans, grains, and seeds, as well as the
leavening of bread, can reduce the binding of zinc by phytic acid and increase zinc bioavailability (1,23). Organic
acids, such as citric acid, can also enhance zinc absorption to some extent (1,23).
Omega-3 fatty acids: Diets that do not include fish, eggs, or generous amounts of algae are generally low in
docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are long-chain n-3 fatty acids important for
cardiovascular health as well as eye and brain development (1). Vegetarians, particularly vegans, have lower
blood levels of DHA and EPA than nonvegetarians (1,24). Diets that do not include fish, eggs, or sea vegetables
generally lack direct sources of DHA and EPA (1). The bioconversion of alpha-linolenic acid (ALA), a plant-based
n-3 fatty acid, to EPA is generally less than 10% in humans, and the conversion of ALA to DHA is substantially
less (1,25). The DRIs for ALA may not be sufficient for vegetarians who consume little if any DHA and EPA (1).
Vegetarians may need more ALA for the conversion to DHA and EPA. Therefore, vegetarian diets should include
high-quality sources of ALA, such as walnuts, flaxseed, flaxseed oil, canola oil, and soy. Vegetarians with
increased n-3 fatty acid requirements (eg, pregnant and lactating women) may benefit from direct sources of
long-chain n-3 fatty acids (eg, cod liver oil, mackerel, salmon, crab, shrimp, and oyster), DHA-fortified foods, eggs
from hens fed DHA-rich microalgae, or a DHA-rich microalgae supplement (1,26). DHA supplements derived from
microalgae are well absorbed and positively affect blood levels of DHA and of EPA through reconversion (1,27).
Soy milk and breakfast bars fortified with DHA are now available in the marketplace (1).
*The Academy of Nutrition and Dietetics has assigned grades, ranging from Grade I (good/strong) to Grade V (insufficient evidence), to
evidence and conclusion statements. The grading system is described in Section III: Clinical Nutrition Management A Reference Guide, page
III-1.