How to cite this article:Gilles RG Monif. Ensuring Adequate Essential Fatty Acid Status
in Vegetarians and Vegans. Adv Res Gastroentero Hepatol, 2020;14(5): 5558967. DOI: 10.19080/ARGH.2020.14.5558967.
Omega-3 and omega-6 fatty acids are essential in the human diet, in that they cannot be synthesized physiologically. The Omega-3 fatty acid, DHA, is highly concentrated in the brain and is important for brain function. Omega-6 fatty acids are also important. They lower harmful LDL cholesterol, boost HDL, and help keep blood sugar in check by improving the body’s sensitivity to insulin. The latest evidence shows that both omega 3 and omega 6 fatty acids are healthy. Therefore omega 6 fatty acids intake does not need to be reduced. However, an increase in Omega 3 fatty acids (ALA) consumption may be necessary in some patients.
Omega-3 fatty acids are present in some plant foods as alpha-linolenic acid (ALA), which can be converted by the body into DHA. Omega-6 fatty acids are found in many plant foods in the form of linolenic acid (LA). Evidence suggests that ALA-derived DHA is sufficient to maintain brain DHA levels and preserve function. There is no evidence of adverse effects on health or cognitive function with lower DHA ingestion levels in vegans. While fish oils provide a source of EPA and DHA which don’t require conversion, the most recent science doesn’t confirm the benefits of fish oil supplements for the prevention and treatment of coronary artery disease. A good supply of ALA is essential for a healthy plant-based diet. This can easily be obtained from plant foods. Patients should warned about the unsubstantiated cardiovascular health claims of fish oil products
The two major classes of polyunsaturated essential fatty acids (PUFAs) are the omega-3 and omega-6 fatty acids. Like all fatty acids, PUFAs consist of long chains of carbon atoms with a carboxyl group at one end of the chain and a methyl group at the other. PUFAs are distinguished from saturated and monounsaturated fatty acids by the presence of two or more double bonds between carbons within the fatty acid chain [1-3].
Both omega-3 and omega-6 fatty acids are essential in that they cannot be synthesized physiologically. Omega-3 fatty acids (omega-3s) have a carbon–carbon double bond located three carbons from the methyl end of the chain. Omega-3s, sometimes referred to as “n-3s,” are present in some plant foods such as soy, flaxseed oil, canola oil, and walnuts, in the form of alpha-linolenic acid (ALA). In animal foods such as oily fish, they are found in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid
(DHA). These are not considered to be essential since they can be converted from ALA . Humans can synthesize DHA from ingested ALA, although this is not an efficient process. The human conversion rate of ALA to EPA and DHA is about 5%–8% [1-3], which seems to be sufficient provided and adequate amount of ALA is ingested.
Omega-6 fatty acids have a carbon-carbon double bond located six carbons from the methyl end of the chain. Omega-6s, “n-6s,” are found in plant foods such as soy, corn, safflower and sunflower oils, nuts and seeds, in the form of linolenic acid (LA). Most humans (except those with inborn errors of metabolism) can convert LA to arachidonic acid (ARA or AA).
The omega-3 fatty acid, Docosahexaenoic acid (DHA), is highly concentrated in the brain and is important for brain function, in part by regulation of cell survival and neuroinflammation [5-9].
DHA is the main n-3 PUFA in the brain as it is concentrated at
levels of about 10,000 nmol/g brain (10–15% of brain fatty acids
or about 5g in an adult brain) , at least 50-fold more than EPA
and 200-fold more than ALA [11-13].
Omega-6 fatty acids are also important. They lower harmful
LDL cholesterol and boost protective HDL. They help keep
hyperglycemia in check by improving the body’s sensitivity to
insulin . Some linolenic acid is converted to arachidonic acid,
a building block for molecules that can promote inflammation,
blood clotting, and the constriction of blood vessels. This fact led
to concern that the consumption of omega-6 fatty acids should
be limited. However, it turns out that very little LA is converted
into ARA, even when LA is abundant in the diet, and ARA is also
converted into molecules that calm inflammation and fight blood
In a science advisory by the American Heart Association
(AHA), nine independent researchers from around the country
found that data from dozens of studies support the cardiovascular
benefits of consuming omega-6 fatty acids . This advisory
was undertaken to summarize the current evidence on the
consumption of omega-6 PUFAs, particularly LA, with respect
to coronary heart disease (CHD) risk. Aggregate data from
randomized trials, case-control and cohort studies, and long-term
animal feeding experiments indicate that the consumption of at
least 5% to 10% of energy from omega-6 PUFAs reduces the risk
of CHD relative to lower intakes. The data also suggest that higher
intakes appear to be safe and may be even more beneficial (as part
of a low–saturated-fat, low-cholesterol diet). In summary, the AHA
supports an omega-6 PUFA intake of at least 5% to 10% of energy
in the context of other AHA lifestyle and dietary recommendations.
To reduce omega-6 PUFA intakes from their current levels would
be more likely to increase than to decrease risk for CHD. The
AHA reviewers found that eating more omega-6 fatty acids didn’t
promote inflammation. Instead, eating more omega-6 fatty acids
either reduced markers of inflammation or left them unchanged.
Omega-6 fatty acids also lower LDL cholesterol and are protective
against heart disease. So, both omega-6 and omega-3 fatty acids
are healthful .
Many other studies have showed that rates of heart disease
went down as consumption of omega-6 fatty acids went up. A metaanalysis
of six randomized trials found that replacing saturated
fat with omega-6 fatty acids reduced the risk of heart attacks and
other coronary events by 24%. A separate report published in the
American Journal of Clinical Nutrition, that pooled the results of
11 large cohorts, showed that replacing saturated fatty acids with
polyunsaturated fatty acids (including omega-6 and omega-3 fatty
acids) reduced heart disease rates more than did replacing them
with monounsaturated fatty acids or carbohydrates .
While there is a theory that omega-3 fatty acids are better for
our health than omega-6 fatty acids, this is not supported by the
latest evidence. Some people have incorrectly thought that the
ratio of n-3 to n-6 fatty acids is important. However, the omega-3
to omega-6 ratio is basically the “good divided by the good,” so it
is of no value in evaluating diet quality or predicting disease .
In the Health Professionals Follow-up Study, for example, the ratio
of omega-6 to omega-3 fatty acids wasn’t linked with risk of heart
disease because both of these were beneficial . Rather than
cutting down on beneficial omega 6, the patient would be better
served by simply increasing their intake of ALA (omega 3).
Since the National Academy of Sciences concluded that there
is inadequate information to set Estimated Average Requirements
(EAR) or the Recommended Dietary Allowance (RDA) for either
LA or ALA for healthy individuals, the Adequate Intake (AI) is used.
The present essential fatty acid AI is based on “the highest median
intake of LA and ALA in United States adults, where a deficiency
is basically nonexistent in non-institutionalized populations” 
(Table 1 & 2).
However, it is unknown if the AIs are beneficial or
physiologically adequate because dose-response data studies are
lacking, Essential fatty acid status is not usually clinically tested, and absence of deficiency symptoms is not necessarily evidence of
adequacy. The rate of DHA uptake into the brain is assumed to be
replacing DHA that is metabolized in the brain, and therefore, can
be used as an estimate for the brain DHA requirement. It has been
reported that the brain DHA uptake rate in humans is between
2.4 and 3.8 mg/day [4,21,22]. Based on current estimates of
ALA consumption in adult males of 1700 mg/day, the percent
conversion of ALA to DHA would need to be 0.14–0.22% to match
the brain DHA requirement . Therefore, it is possible that even
a small amount of DHA synthesis may be sufficient to meet adult
brain DHA uptake demands.
In pre-menopausal women, there is evidence that significant
changes in DHA status can occur independent of changes in n-3
PUFA intake, likely through increased synthesis of DHA from ALA.
For example, women have higher DHA in plasma phospholipids
and erythrocytes compared with men , which is associated
with much higher rates of DHA synthesis in women [1,2,24].
Studies of premenopausal women reported a higher capacity of
ALA conversion, and a more efficient conversion of ALA to EPA
and DHA compared to men . In 21 days, women incorporated
700 mg of radioactive labeled [U-13C]-ALA, and resulted in
a net fractional ALA interconversion of 21% of EPA, 6% of
docosapentaenoic acid (can be converted to DHA), and 9% of DHA
in plasma which led the researchers to postulate that increased
conversion was due to either an estrogen catalyzed conversion or
an increased need for EPA and DHA during pregnancy and fetal
One study did not find any associations between dietary EPA,
DHA, or the n–6 PUFA and birth weight. In contrast, the results
indicate a growth-promoting effect of ALA intake, with the
increase in birth weight being independent of gestational age at
birth. It is noteworthy that no specific function has been assigned
to ALA itself other than serving as a source of energy or conversion
to EPA and DHA. Therefore, any mechanisms of improvement in
birth weight are most likely via desaturation and elongation to its
longer-chain derivatives. Although conversion rates of ALA into
the longer-chain EPA and DHA are modest with the estimated
fractional conversion reported to be less than 5% , increased
ALA intake has demonstrated to increase proportions of longchain
n–3 fatty acids in plasma and cell lipids to reproduce
beneficial effects . Specifically, in pregnancy, the levels of DHA
and ARA increase in cord blood in relation to circulating levels of
ALA and LA in maternal blood .
Sales of fish oil supplements reached $1.84 billion in 2018
indicating widespread use. However, the most recent science
doesn’t confirm the benefits of fish oil supplements for the
prevention and treatment of coronary artery disease. The initial
reasoning for recommending fish oil supplements was based on
studies of the Eskimo. It was mistakenly thought that the Eskimo
suffered less from atherosclerosis and from coronary artery
disease in particular. However, it is now known that the Eskimo
do not have lower rates of coronary artery disease. One study
concluded that the “Greenland Eskimos and the Canadian and
Alaskan Inuit have CAD as often as the non-Eskimo populations
.” Another study showed “Eskimos have CHD despite high
consumption of omega-3 fatty acids .” A meta study of the
efficacy of fish oil summarizes their results as follows: “All of the
studies included were the gold-standard kind of clinical trial --
with people assigned at random to either take fish oil or a placebo.
The studies ranged in length from one to nearly five years. The
authors detected no reduction in any cardiovascular events, such
as heart attacks, sudden death, angina, heart failures, strokes, or
death, no matter what dose of fish oil used .”
The most plentiful dietary n-6 polyunsaturated essential fatty
acid is LA. Omega-6 fatty acid food sources commonly consumed
by vegans include nuts, seeds, certain vegetables, and vegetables
oils such as soybean oil, safflower oil, and corn oil among others.
Therefore, any diet that is plant-based leads to a high dietary
intake of LA . Ensuring adequate essential fatty acids in vegans
therefore focuses on obtaining an adequate intake of the omega 3
fatty acid, ALA. There is evidence that DHA synthesis from ALA can
be sufficient to maintain brain function. For example, vegetarians
and vegans, in which DHA derived from ALA is the sole source
of DHA, have DHA levels comparable to omnivores . Some
studies show that their DHA levels are lower than omnivores
[31-33] but have neurological disease rates comparable to
omnivores [34-37], suggesting that ALA-derived DHA is sufficient
to maintain brain function in these individuals. In addition,
dietary ALA, with no DHA, is sufficient to completely restore brain
DHA in rats  and non-human primates . Taken together,
evidence suggests that ALA-derived DHA is sufficient to maintain
brain DHA levels and preserve function . There is no evidence
of adverse effects on health or cognitive function with lower DHA
ingestion levels in vegans .
One study showed that vegetarians give birth to infants with
less DHA in their plasma and cord artery phospholipids but this
did not appear to be independently related to the outcome of
(Table 3) Generally, if a patient’s food history doesn’t include
good sources of ALA then foods that are good sources of ALA should
be prescribed. If the patient isn’t compliant, then supplements
can be prescribed. While the conversion of ALA to DHA rates in
women are higher, if the intake of rich sources of ALA are not being
consumed then supplements should be prescribed. Infant formula
is available enriched with DHA. Plant-based sources of omega-
3s from algal oil usually provide around 100–300 mg DHA and some contain EPA as well. These supplements typically contain
omega-3s in the triglyceride form . According to a small study,
the bioavailability of DHA from algal oil is equivalent to that from
cooked salmon . In one study vegans responded robustly to a
relatively low dose of a vegan DHA and EPA supplement .
A good supply of ALA is essential for a healthy plant-based
diet. This can easily be obtained from plant foods. Patients should
warned about the unsubstantiated cardiovascular health claims
of fish oil products.
Institute of Medicine (IOM) (2005) Dietary fats: Total fat and fatty acids. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academics Press, Washington, DC, USA.