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Health effects of vegan diets
1–3
Winston J Craig
ABSTRACT
Recently, vegetarian diets have experienced an increase in popular-
ity. Avegetarian diet is associated with many health benefits because
of its higher content of fiber, folic acid, vitamins C and E, potassium,
magnesium, and many phytochemicals and a fat content that is more
unsaturated. Compared with other vegetarian diets, vegan diets tend
to contain less saturated fat and cholesterol and more dietary fiber.
Vegans tend to be thinner, have lower serum cholesterol, and lower
blood pressure, reducing their risk of heart disease. However, elim-
inating all animal products from the diet increases the risk of certain
nutritional deficiencies. Micronutrients of special concern for the
vegan include vitamins B-12 and D, calcium, and long-chain n–3
(omega-3) fatty acids. Unless vegans regularly consume foods that
are fortified with these nutrients, appropriate supplements should be
consumed. In some cases, iron and zinc status of vegans may also be
of concern because of the limited bioavailability of these
minerals. Am J Clin Nutr 2009;89(suppl):1627S–33S.
INTRODUCTION
A nationwide poll conducted in April 2006 by Harris In-
teractive reported that 1.4% of the American population is vegan,
in that they eat no meat, fish, dairy, or eggs (1). Vegan diets are
growing in popularity today among teenagers and youth, espe-
cially females. For many vegans, nutritional choices center
around taking better care of the earth’s resources and the envi-
ronment, ethical issues about animal care, the use of antibiotics
and growth stimulants for the production of animals, the threat
of animal-borne diseases, and the health advantages of a plant-
based diet (2–6). In addition, the potential of allergies from dairy
products and lactose intolerance have fueled the popularity of
soy-based dairy substitutes.
What then is the nutritional and health status of those who
follow a vegan diet? Compared with other vegetarians (eg,
lactoovovegetarians), are there any advantages or disadvantages
to following a vegan diet? Does the elimination of dairy and eggs
offer any additional benefits or create potential concerns? The
purpose of this brief review is to summarize current knowledge
on the health effects of vegan diets, to discuss the nutritional
concerns or shortfalls of a vegan diet and to provide some
practical dietary recommendations for following a healthy vegan
diet. Key et al (7) have provided a pertinent overview of the
health effects of vegetarian diets, focusing on their European
Prospective Investigation into Cancer and Nutrition–Oxford
(EPIC-Oxford) study and other large population studies.
HEALTH EFFECTS OF VEGAN DIETS
Vegan diets are usually higher in dietary fiber, magnesium,
folic acid, vitamins C and E, iron, and phytochemicals, and they
tend to be lower in calories, saturated fat and cholesterol, long-
chain n–3 (omega-3) fatty acids, vitamin D, calcium, zinc, and
vitamin B-12 (8). In general, vegetarians typically enjoy a lower
risk of cardiovascular disease (CVD), obesity, type 2 diabetes,
and some cancers (3). A vegan diet appears to be useful for
increasing the intake of protective nutrients and phytochemicals
and for minimizing the intake of dietary factors implicated in
several chronic diseases (9). In a recent report (10), different
plant food groups were rated with respect to their metabolic-
epidemiologic evidence for influencing chronic disease reduc-
tion. According to the evidence criteria of the World Health
Organization and Food and Agriculture Organization (WHO/
FAO), cancer risk reduction associated with a high intake of fruit
and vegetables was assessed as probable or possible, risk of
CVD reduction as convincing, whereas lower risk of osteopo-
rosis was assessed as probable (10). The evidence for a risk-
reducing effect of consuming whole grains was assessed as
possible for colorectal cancer and probable for type 2 diabetes
and CVD. The evidence for a risk-reducing effect of consuming
nuts was assessed as probable for CVD (10).
Cardiovascular disease
In summarizing the published research, Fraser (11) noted that,
compared with other vegetarians, vegans are thinner, have lower
total and LDL cholesterol, and modestly lower blood pressure.
This is true not only for whites; work by Toohey et al (12) showed
that blood lipids and body mass index (BMI; in kg/m
2
)were
significantly lower in African American vegans than in lacto-
ovovegetarians. Similarly, among Latin Americans, vegetarians
had lower plasma lipids than did their omnivore counterparts,
with the lowest reported among vegans (13). In that study, plasma
total and LDL cholesterol were 32% and 44% lower among ve-
gans than among omnivores. Because obesity is a significant risk
factor for CVD, the substantially lower mean BMI observed in
1
From the Department of Nutrition and Wellness, Andrews University,
Berrien Springs, MI.
2
Presented at the symposium, ‘‘Fifth International Congress on Vegetar-
ian Nutrition,’’ held in Loma Linda, CA, March 4–6, 2008.
3
Reprints not available. Address correspondence to WJ Craig, Depart-
ment of Nutrition and Wellness, Andrews University, Marsh Hall, Room
301, Berrien Springs, MI 49104-0210. E-mail: wcraig@andrews.edu.
First published online March 11, 2009; doi: 10.3945/ajcn.2009.26736N.
Am J Clin Nutr 2009;89(suppl):1627S–33S. Printed in USA. Ó2009 American Society for Nutrition 1627S
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vegans may be an important protective factor for lowering blood
lipids and reducing the risk of heart disease (8).
Vegans, compared with omnivores, consume substantially greater
quantities of fruit and vegetables (14–16). A higher consumption of
fruit and vegetables, which are rich in fiber, folic acid, anti-
oxidants, and phytochemicals, is associated with lower blood
cholesterol concentrations (17), a lower incidence of stroke, and
a lower risk of mortality from stroke and ischemic heart disease
(18, 19). Vegans also have a higher consumption of whole
grains, soy, and nuts (14, 15, 20), all of which provide significant
cardioprotective effects (21, 22).
Cancer
Data from the Adventist Health Study showed that non-
vegetarians had a substantially increased risk of both colorectal
and prostate cancer than did vegetarians (23). A vegetarian diet
provides a variety of cancer-protective dietary factors (24). In
addition, obesity is a significant factor, increasing the risk of
cancer at a number of sites (25). Because the mean BMI of
vegans is considerably lower than that of nonvegetarians (8), it
may be an important protective factor for lowering cancer risk.
Vegans consume considerably more legumes, total fruit and
vegetables, tomatoes, allium vegetables, fiber, and vitamin C than
do omnivores (14–16, 20, 23). All those foods and nutrients are
protective against cancer (25). Fruit and vegetables are described
as protective against cancer of the lung, mouth, esophagus, and
stomach and to a lesser degree some other sites, whereas the
regular use of legumes provides a measure of protection against
stomach and prostate cancer. In addition, fiber, vitamin C, car-
otenoids, flavonoids, and other phytochemicals in the diet are
shown to exhibit protection against various cancers, whereas al-
lium vegetables provide protection against stomach cancer, and
garlic against colorectal cancer. Foods rich in lycopene, such as
tomatoes, are known to protect against prostate cancer (25).
Fruit and vegetables are known to contain a complex mix-
ture of phytochemicals that possess potent antioxidant and anti-
proliferative activity and show additive and synergistic effects (24,
26). The phytochemicals interfere with several cellular processes
involved in the progression of cancer. These mechanisms include
inhibiting cell proliferation, inhibition of DNA adduct formation,
inhibiting phase 1 enzymes, inhibiting signal transduction path-
ways and oncogene expression, inducing cell-cycle arrest and
apoptosis, inducing phase 2 enzymes, blocking the activation of
nuclear factor-jB, and inhibiting angiogenesis (24).
With this wide array of useful phytochemicals in thevegetarian
diet, it is surprising that population studies have not shown more
pronounced differences in cancer incidence or mortality rates
between vegetarians and nonvegetarians (7, 27). The bioavail-
ability of the phytochemicals, which depends among other
things on food preparation methods, may be an important de-
termining factor. However, new evidence suggests that a low
vitamin D status, a problem often reported in vegan populations
(8, 28), is associated with an increased risk of cancers (29, 30).
The sources of protein avoided or consumed by vegans also
have definite health consequences. Red meat and processed meat
consumption are consistently associated with an increase risk of
colorectal cancer (25). Those in the highest quintile of red meat
intake had elevated risks, ranging from 20% to 60%, of esoph-
ageal, liver, colorectal, and lung cancers than did those in the
lowest quintile of red meat intake (31). In addition, the use of
eggs was recently shown to be associated with a higher risk of
pancreatic cancer (32). Although vegans avoid consuming red
meat and eggs altogether, they consume greater amounts of le-
gumes than do omnivores (14, 16, 20). This protein source was
seen in the Adventist Health Study to be negatively associated
with risk of colon cancer (23). New data suggest that legume
intake is also associated with a moderate reduction in the risk of
prostate cancer (33). In Western society, vegans also consume
substantially more tofu and other soy products than do omni-
vores (14, 16). Consumption of isoflavone-containing soy prod-
ucts during childhood and adolescence protects women against
the risk of breast cancer later in life (34), whereas a high
childhood dairy intake has been associated with an elevated risk
of colorectal cancer in adulthood (35). Cancer risk in vegans
may be altered because vegans consume soy beverages rather
than dairy beverages. Data from the Adventist Health Study
showed that consumption of soy milk by vegetarians protected
them against prostate cancer (36), whereas in other studies the
use of dairy was associated with an increased risk of prostate
cancer (25, 37–39).
Further research is needed to explore the relation between
consuming plant-based diets and risk of cancer because there are
many unanswered questions about how diet and cancer are con-
nected. To date, epidemiologic studies have not provided convincing
evidence that a vegan diet provides significant protection against
cancer. Although plant foods contain many chemopreventive
factors, most of the research data comes from cellular bio-
chemical studies.
Bone health
Cross-sectional and longitudinal population-based studies pub-
lished within the past 2 decades suggest no differences in bone
mineral density (BMD), for both trabecular and cortical bone,
between omnivores and lactoovovegetarians (40). More recent
studies with postmenopausal Asian women showed spine or hip
BMD was significantly lower in long-term vegans (41, 42). Those
Asian women, who were vegetarian for religious reasons, had low
intakes of protein and calcium. An inadequate protein and low
calcium intake has been shown to be associated with bone loss and
fractures at the hip and spine in the elderly (43, 44). Adequate
calcium intake may be a problem for vegans. Although lacto-
ovovegetarians generally consume adequate amounts of calcium,
vegans typically fall short of the recommended daily intake for
calcium (8, 45, 46). Results from the EPIC-Oxford study provide
good evidence that the risk of bone fractures for vegetarians was
similar to that of omnivores (46). The higher risk of bone fracture
seen in vegans appears to be a consequence of a lower mean
calcium intake. No difference was observed between the fracture
rates of the vegans who consumed .525 mg calcium/d and the
omnivore fracture rates (46).
Bone health depends on more than just protein and calcium
intakes. Research has shown that bone health is also influenced by
nutrients such as vitamin D, vitamin K, potassium, and magnesium
and by foods such as soy and fruit and vegetables (47–50). Vegan
diets do well in providing a number of those important sub-
stances. The maintenance of acid-base balance is critical for bone
health. A drop in extracellular pH stimulates bone resorption (51),
because bone calcium is used to buffer the pH drop. An acid-
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forming diet, therefore, increases urinary calcium excretion (52).
However, a diet rich in fruit and vegetables that is typical of
a vegan diet has a positive effect on the calcium economy and
markers of bone metabolism in men and women (49). The high
potassium and magnesium content of fruit and vegetables pro-
vides an alkaline ash, which inhibits bone resorption (53). Higher
intakes of potassium are associated with greater BMD of the
femoral neck and lumbar spine of premenopausal women (54).
Blood concentrations of undercarboxylated osteocalcin, a sen-
sitive marker of vitamin K status, is considered an indicator of hip
fracture (55) and a predictor of BMD (56). Results from 2 large,
prospective cohort studies support an association between vita-
min K intake and relative risk of hip fracture. In the Nurses’
Health Study, middle-aged women consuming the most vitamin
K had the lowest risk of hip fracture. Risk of hip fracture was
decreased 45% for 1 servings/d of green leafy vegetables (the
main vitamin K source) compared with 1 serving/wk (57). In
the Framingham Heart Study, elderly men and women in the
highest quartile of vitamin K intake had a 65% decreased risk of
hip fracture than did those in the lowest quartile (58).
In addition to a high intake of fruit and vegetables, vegans also
tend to have a high intake of tofu and other soy products (14, 16).
Soy isoflavones are suggested to have a beneficial effect on bone
health in postmenopausal women (50). In a meta-analysis of 10
randomized controlled trials, soy isoflavones showed a signifi-
cant benefit to spine BMD of menopausal women (59). In an-
other meta-analysis, soy isoflavones significantly inhibited bone
resorption and stimulated bone formation compared with pla-
cebo (60). In a randomized clinical trial lasting 24 mo involving
osteopenic postmenopausal women, increases in BMD of both
lumbar spine and femoral neck were substantially greater with
the soy isoflavone, genistein, than with placebo (61).
As long as the calcium and vitamin D intake of vegans is
adequate, their bone health is probably not an issue because their
diet contains an ample supply of other protective factors for bone
health. However, more studies are needed to provide more de-
finitive data on the bone health of vegans.
POTENTIAL NUTRITIONAL SHORTFALLS
To obtain a nutritionally adequate diet, the consumer must first
have an appropriate knowledge of what constitutes a nutritionally
adequate diet. Second, accessibility is important, ie, the avail-
ability of certain foodstuffs and foods fortified with key nutrients
that are otherwise lacking in the diet. This accessibility will vary
greatly, depending on the geographic region of the world, because
different countries have different fortification laws. The fol-
lowing section deals with nutrients of concern in the vegan diet.
The problem of insufficient calcium has already been discussed in
the section on bone health.
n–3 Polyunsaturated fat
Diets that do not include fish, eggs, or sea vegetables (sea-
weeds) generally lack the long-chain n–3 fatty acids, eicosa-
pentaenoic acid (EPA; 20:5n23) and docosahexaenoic acid
(DHA; 22:6n23), which are important for cardiovascular health
as well as eye and brain functions. The plant-based n–3 fatty
acid a-linolenic acid (ALA; 18:3n23) can be converted into
EPA and DHA, albeit with a fairly low efficiency (62, 63).
Compared with nonvegetarians, vegetarians, and especially ve-
gans, tend to have lower blood concentrations of EPA and DHA
(64). However, vegans can obtain DHA from microalgae sup-
plements containing DHA, as well as from foods fortified with
DHA. However, EPA can be obtained from the retroconversion
of DHA in the body. The oil from brown algae (kelp) has also
been identified as a good source of EPA.
The new Dietary Reference Intakes recommend intakes of 1.6
and 1.1 g ALA/d for men and women, respectively, which ac-
counts for ,1% of the daily calories. Presently, the intake of EPA
plus DHA in the United States is only 0.1–0.2 g/d, with the DHA
intake being ’2–3 times the intake of EPA (65). Vegans should
be able to easily reach the n–3 fatty acid requirements by in-
cluding regular supplies of ALA-rich foods in their diet and also
DHA-fortified foods and supplements. However, DHA supple-
ments should be taken with caution. Although they can lower
plasma triacylglycerol, they can raise total and LDL cholesterol
(66, 67), cause excessively prolonged bleeding times, and impair
immune responses (65).
Vitamin D
In the EPIC-Oxford study, vegans had the lowest mean intake
of vitamin D (0.88 lg/d), a value one-fourth the mean intake of
omnivores (8). For a vegan, vitamin D status depends on both
sun exposure and the intake of vitamin D-fortified foods. Those
living in areas of the world without fortified foods would need to
consume a vitamin D supplement. Living at high latitudes can
also affect one’s vitamin D status, because sun exposure in that
region is inadequate for several months of the year (68). Those
who are dark skinned, elderly, who extensively cover their body
with clothing for cultural reasons, and who commonly use
sunscreen are at an increased risk of vitamin D deficiency (45).
Another matter of concern for vegans is that vitamin D
2
, the
form of vitamin D acceptable to vegans, is substantially less
bioavailable than the animal-derived vitamin D
3
(69).
In Finland, the dietary intake of vitamin D in vegans was in-
sufficient to maintain serum 25-hydroxyvitamin D and parathy-
roid hormone concentrations within normal ranges in the winter,
which appeared to have a negative effect on long-term BMD (28).
Throughout the year serum 25-hydroxyvitamin D concentrations
were lower and parathyroid hormone higher in vegan women than
in omnivores and other vegetarians. BMD in the lumbar region of
the spine was 12% lower in vegans than in omnivores.
Iron
Heme iron absorption is substantially higher than non-heme iron
from plant foods. However, hemoglobin concentrations and the
risk of irondeficiency anemia are similar for vegans compared with
omnivores and other vegetarians (70). Vegans often consume large
amounts of vitamin C–rich foods that markedly improve the ab-
sorption of the nonheme iron. Serum ferritin concentrations are
lower in some vegans, whereas the mean values tend to be similar
to the mean values of other vegetarians but lower than the mean
value for omnivores (71). The physiologic significance of low
serum ferritin concentrations is uncertain at this time.
Vitamin B-12
Compared with lactoovovegetarians and omnivores, vegans
typically have lower plasma vitamin B-12 concentrations, higher
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prevalence of vitamin B-12 deficiency, and higher concentrations
of plasma homocysteine (72). Elevated homocysteine has been
considered a risk factor for CVD (73) and osteoporotic bone
fractures (74). Vitamin B-12 deficiency can produce abnormal
neurologic and psychiatric symptoms that include ataxia, psy-
choses, paresthesia, disorientation, dementia, mood and motor
disturbances, and difficulty with concentration (75). In addition,
children may experience apathy and failure to thrive, and macro-
cytic anemia is a common feature at all ages.
Zinc
Vegetarians are often considered to be at risk for zinc deficiency.
Phytates, a common component of grains, seeds, and legumes,
binds zinc and thereby decreases its bioavailability. However,
a sensitive marker to measure zinc status in humans has not been
well established, and the effects of marginal zinc intakes are
poorly understood (76). Although vegans have lower zinc intake
than omnivores, they do not differ from the nonvegetarians in
functional immunocompetence as assessed by natural killer cell
cytotoxic activity (14). It appears that there may be facilitators of
zinc absorption and compensatory mechanisms to help vegeta-
rians adapt to a lower intake of zinc (77).
DIETARY RECOMMENDATIONS FOR OPTIMAL VEGAN
DIETS
1) To avoid B-12 deficiency, vegans should regularly consume
vitamin B-12–fortified foods, such as fortified soy and rice
beverages, certain breakfast cereals and meat analogs, and
B-12–fortified nutritional yeast, or take a daily vitamin B-12
supplement. Fermented soy products, leafy vegetables, and
seaweed cannot be considered a reliable source of active vi-
tamin B-12. No unfortified plant food contains any significant
amount of active vitamin B-12.
2) To ensure adequate calcium in the diet, calcium-fortified plant
foods should be regularly consumed in addition to consuming
the traditional calcium sources for a vegan (green leafy vege-
tables, tofu, tahini). The calcium-fortified foods include ready-
to-eat cereals, calcium-fortified soy and rice beverages,
calcium-fortified orange and apple juices, and other beverages.
The bioavailability of the calcium carbonate in the soy bever-
ages and the calcium citrate malate in apple or orange juice is
similar to that of the calcium in milk (78, 79). Tricalcium
phosphate–fortified soy milk was shown to have a slightly
lower calcium bioavailability than the calcium in cow milk
(78).
3) To ensure an adequate vitamin D status, especially during the
winter, vegans must regularly consume vitamin D–fortified
foods such as soy milk, rice milk, orange juice, breakfast
cereals, and margarines that are fortified with vitamin D.
Where fortified foods are unavailable, a daily supplement of
5–10 lg vitamin D would be necessary. The supplement would
be highly desirable for elderly vegans.
4) A vegan should regularly consume plant foods naturally rich in
the n–3 fatty acid ALA, such as ground flaxseed, walnuts,
canola oil, soy products, and hemp seed–based beverages. In
addition, it is recommended that vegans consume foods that
are fortified with the long-chain n–3 fatty acid DHA, such as
some soy milks and cereal bars. Those with increased require-
ments of long-chain n–3 fatty acids, such as pregnant and
lactating women, would benefit from using DHA-rich micro-
algae supplements.
5) Because of the high phytate content of a typical vegan diet, it
is important that a vegan consume foods that are rich in zinc,
such as whole grains, legumes, and soy products, to provide
a sufficient zinc intake. Benefit could also be obtained by
vegans consuming fortified ready-to-eat cereals and other
zinc-fortified foods.
A more comprehensive list of eating guidelines for vegans is
available elsewhere (80).
FURTHER RESEARCH NEEDED
The term vegetarian is often used to describe a whole range
of diets practiced with varying degrees of restriction, making it
a challenge to meaningfully compare and contrast the health
benefits of various vegetarian diets. Although preliminary data
are valuable, more scientific studies on vegans are needed to get
a clearer picture of their health status (7, 11). Current data show
that vegans have a lower risk of heart disease than do omnivores
and other vegetarians, but there are too few studies on other risk
factors for definitive conclusions. One small pilot trial has
shown that a vegan diet improves glycemic control in in-
dividuals with type 2 diabetes (81), but more studies are needed
that look at the effects of a vegan diet on the risk of diabetes, as
well as cancer. On the basis of our present knowledge, vegans do
not appear likely to have any significant advantages over other
vegetarians about chronic disease patterns (11). The vegan
studies that do exist often involve only a small number of sub-
jects. More studies are also needed with long-term vegans be-
cause the health advantages appear more clearly defined when
a person has been following a plant-based diet for .5 y (82).
Research is also needed to investigate whether the age at which
a vegan diet is adopted has any influence on health outcomes.
SUMMARY
Vegans are thinner, have lower serum cholesterol and blood
pressure, and enjoy a lower risk of CVD. BMD and the risk of
bone fracture may be a concern when there is an inadequate
intake of calcium and vitamin D. Where available, calcium- and
vitamin D–fortified foods should be regularly consumed. There
is a need for more studies on the relation between vegan diets
and risk of cancer, diabetes, and osteoporosis. Vitamin B-12
deficiency is a potential problem for vegans, so that the use of
vitamin B-12–fortified foods or supplements are essential. To
optimize the n–3 fatty acid status of vegans, foods rich in ALA,
DHA-fortified foods, or DHA supplements should be regularly
consumed. Vegans generally have an adequate iron intake and do
not experience anemia more frequently than others. Typically,
vegans can avoid nutritional problems if appropriate food choices
are made. Their health status appears to be at least as good as
other vegetarians, such as lactoovovegetarians. (Other articles in
this supplement to the Journal include references 83–109.)
The author had no financial disclosures to report.
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