The Fishy Dilemma of Omega-3s

Omega-3 fatty acids are a hot topic of conversation among those interested in nutrition these days.  Over the past few decades the scientific world has cycled through several different recommendations for Omega-3s.  During the 1980s, studies found that eating fatty fish seemed to cause a 29% reduction in cardiovascular death (1).  Subsequent studies refuted this with results showing that eating fish or taking fish oil supplements was actually linked to a higher risk of cardiovascular death (2,3).  It took until 2012 though, when a comprehensive meta-analysis found a lack of benefit from omega-3 supplementation for cardiovascular health, to realize that generalized recommendations to increase fish intake or to take fish oil capsules were not warranted (4,5,6).

On other fronts, research was looking at the effects of omega-3 fatty acids on brain health.  A double-blind randomized interventional study found that consuming supplemental omega-3s showed improvements in cognitive functions and significantly less brain shrinkage in older adults (7).  Another study showed that people with higher blood levels of omega-3 fatty acids were more likely to reveal healthier brains on MRI (8).  Confounding these findings, more recent studies have not found any link between omega-3 supplements and healthier brains or slowed cognitive decline (9).

In addition, other investigations suggest that omega-3 supplementation may increase the risk of prostate cancer by up to 43% (10) although some researchers question the validity of this report and recommend further review before coming to a final conclusion (11,12).  It is quite possible that this increase in risk is not due to the omega-3s themselves but to the source of the fat being ingested (meat and other animal products, processed foods, high-ALA oils such as soybean and canola oil and foods cooked in oil) as well as a lack of antioxidants in the diet.  Other research discovered that adding 3 tablespoons of ground flaxseed (a food very high in the omega-3 ALA) to the daily diet consistently decreased prostate cancer cell proliferation (13, 14).

Controversy abounds but, at this point in time, omega-3 fatty acids are considered to be important for healthy brain development throughout life.  Hopefully, ongoing research will clarify and update our information on the comprehensive health effects of omega-3 fatty acids.


What are omega-3 fatty acids?

Before going any further, here is a quick overview of omega-3 fatty acids.

There are three basic types of fat in our diet – saturated fats, trans-fats and unsaturated fats.

Unsaturated fats include polyunsaturated fat and monounsaturated fat.

Polyunsaturated fat is made up of omega-3 and omega-6 fatty acids.  Both of these are “essential” fatty acids because they cannot be produced by our bodies but must be obtained from an outside source.

Sufficient amounts of both omega-3 and omega-6 polyunsaturated acids are necessary for health.

Omega-6s are overly plentiful in our modern diet.  Omega-6s tend to be inflammatory, causing increased blood clotting, constriction of blood vessels, increases in cell division and suppression of immune function.

Omega-3s are less abundant in today’s diets.  Omega-3s are generally anti-inflammatory and reduce blood clotting, improve blood flow, decrease cell division and enhance immune function.

Within the omega-3 fatty acid family are three major types – alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

ALA is a short-chain fatty acid; EPA and DHA are long-chain fatty acids.  EPA and DHA are the biologically active forms of omega-3s (15,13).

Omega-3 fatty acids are an important part of cell membranes throughout the body.  They are necessary for muscle activity, blood clotting, cell growth, digestion, fertility and nervous system function.  They are found in large quantities in the brain and nervous system.  They also act as signaling molecules with wide-reaching functions on human cardiovascular, pulmonary, immune and endocrine body systems (15,13).


What are the recommended daily amounts of omega-3 fatty acids?

The amount of omega-3s required for health is quite small.  The National Academy of Medicine provides daily intake recommendations only for ALA since ALA is the only omega-3 that is considered “essential”.  This is because EPA and DHA can be produced in the human body from ALA.

The amounts listed here are the Adequate Intakes (AI) of ALA which are amounts that are associated with low risk of developing a condition related to a deficiency of the nutrient (15,17).


Birth to 12 months (total omega-3s)                        0.5 gm

Children 1 – 3 years                                                      0.7 gm

Children 4 -8 years                                                       0.9 gm

Boys 9 – 13 years                                                           1.2 gm

Girls 9 – 13 years                                                           1.0 gm

Teen boys 14 – 18 years                                                1.6 gm

Teen girls 14 – 18 years                                                 1.1 gm

Men                                                                                   1.6 gm

Women                                                                             1.1 gm

Pregnant teens and women                                          1.4 gm

Breastfeeding teens and women                                  1.3 gm



What are good plant-based sources of ALA?

Eating plants can provide more than enough ALA for health.  Seeds and nuts are the best sources.  Leafy greens and beans are excellent as well and most vegetables and fruits supply smaller amounts.

The simple step of adding a tablespoonful or two of ground flaxseed or chia seeds to your daily diet will provide you with enough ALA.


The following are some examples of good plant sources of ALA (18,19,20);

Nuts and seeds

Flaxseeds – 15 gm                            3.22 gm

Chia seeds – 15 gm                           2.69 gm

Hemp seeds – 15 gm                       1.30 gm

Walnuts – 30 gm                              1.89 gm

Pecan nuts – 30 gm                         0.186 gm

Hazelnuts – 30 gm                           0.036 gm

Tahini – 30 gm                                  0.036 gm


Beans and other Legumes

Navy beans – 1 cup                          1.12 gm

Kidney beans  – 1 cup                      0.403 gm

Black beans – 1 cup                         0.667 gm

Canned baked beans – 1 cup         0.446 gm

Edamame (frozen)- 1 cup              0.555 gm

Soy milk – 1 cup                              0.280 gm

Note:  Chickpeas are a legume exception.  They contain a high level of omega-6s with a ratio of 26:1 omega-6:omega-3.



Sweet peppers – ½ cup                  0.930 gm

Yellow onions – ½ cup                    0.792 gm

Cauliflower – 1 cup                          0.401 gm

Winter squash – 1 cup                    0.396 gm

Potatoes – 1 cup                               0.267 gm

Brussels sprouts – 1 cup                 0.270 gm

Broccoli – 1 cup                                 0.187 gm

Kale (raw) – 100 gm                        0.180 gm

Arugula (raw) – 100 gm                 0.170 gm

Spinach (raw) – 100 gm                 0.138 gm



Raspberries – 1 cup                         0.300 gm

Blueberries (frozen) – 1 cup         0.270 gm

Avocados – 1 cup                            0.255 gm

Bananas – 1 cup                              0.065 gm

Strawberries (frozen) – 1 cup      0.055 gm

Raisins  – ¼ cup                             0.037 gm


What about the long-chain omega-3s, EPA and DHA, in a plant-based diet?

Certain fish, eggs and microalgae are good sources of pre-formed EPA and DHA.  Of course, people on a plant-based diet do not eat fish or eggs and, perhaps surprisingly, not eating fish is a positive factor for health.  Fish contains significant amounts of noxious substances such as heavy metals (mercury, lead, cadmium); dioxins; PCBs (polychlorinated biphenyls); pesticides such as DDT; and flame-retardant chemicals, all of which are toxic to human beings.  Unfortunately, the amounts of these pollutants in fish are rising (21).  Mercury ingestion alone can have far-ranging consequences in humans including damaging changes to the central nervous system and the cardiovascular system (22). It is not uncommon for consumers who eat several meals of fish in a week to exceed the safe levels of mercury described by the Environmental Protection Agency (EPA) (23).   Compounding the problem, a 2014 report from the Environmental Working Group points out two strikes against eating fish – not only are many of the most popular seafoods high in mercury content, they are also low in omega-3 fatty acids (24).  Omega-3 supplements are not necessarily safe either.  Analysis of fish oil products has revealed the presence of persistent organic pollutants such as PCBs and organochlorine pesticides in distilled fish oils (25,26). However, fish oils are generally low in mercury and other heavy metals as they are removed during processing and purification (27).

Plants contain ALA, not the longer chain omega-3s, EPA and DHA.  However, the human body is able to convert ALA into EPA and then the EPA into DHA.   Yet this process is not straightforward.  To understand the problem, we need to go back in history.  Even as recently as 100 years ago, and certainly for all of our evolution as humans, our diets were fairly equally balanced between omega-6 and omega-3 fatty acids.  Many of the foods that we eat today that are so high in omega-6s, especially processed foods and oils isolated from plants, were scarce if available at all in our past.  When omega-6 and omega-3 fatty acids are present in the diet in more or less equivalent amounts, humans easily convert ALA to EPA and DHA.  This ability was important in early humans who were not located near an ocean for easy access to fish.  Nor were eggs easily attainable. Our modern diets are much different, with processed foods and isolated oils as near as the local grocery store.  The ratio of omega-6 to omega-3 in our food, once close to 1:1, is now closer to 10:1 and even higher (28,29).  The difficulty is that the enzymes that metabolize both omega-3s and omega-6s are exactly the same ones.  Though they usually favour omega-3 over omega-6 fatty acids as a substrate, there is a point at which too many omega-6s overwhelm the enzymes and the conversion of omega-3s into EPA and DHA is greatly reduced (30,13).

Research has shown us that the conversion of ALA into EPA and DHA in the human body is generally low, with less than 15% of ALA being converted (31).  Studies looking at people who eat fish compared with those who don’t are varied in the EPA and DHA levels in their participants.  Some research has found that fish-eaters have higher levels of EPA and DHA on average than non-fish-eaters; others show similar levels in fish-eaters and non-fish eaters.  One large study that including 14,422 participants found that, despite ingesting significantly less or no fish or fish oil at all, blood levels of the long-chain omega-3s in vegans, both men and women, were equivalent to those of fish-eaters, meat-eaters and lacto-ovo-vegetarians (32).  Researchers suggested that conversion of ALA to EPA and DHA by the body is increased when blood levels of long-chain omega-3s are much lower than ALA levels in the diet.  In fact, this study noted that the actual amount of ALA converted to long-chain omega-3s was almost double in vegan men and women compared to fish eaters (32,33).


What factors affect conversion of ALA to EPA/DHA?

Though we know that our bodies can convert ALA into their more biologically active forms of EPA and DHA, the amount of conversion that actually occurs is unpredictable and influenced by many variables.  Studies suggest that rates of ALA to EPA conversion can range from 0.3% to 21% and, for DHA, from zero to 9% (34,35) and it is difficult to know the conversion rate of your own body.


Here are some factors that influence the conversion rate of ALA into EPA and DHA in your body;

  • Consuming direct sources of DHA such as fish or eggs can depress the conversion by 70% or more (34,36).
  • The hormone estrogen seems to boost DHA synthesis, especially during the childbearing years. Indeed, women generally experience higher conversion rates than men (28).  Studies have observed an average 15% higher DHA level in women compared with men (37).
  • Genetic differences in the desaturase enzymes that are important for the conversion can either speed up or slow down the reaction. Research suggests that 40% of the inter-individual variation in ALA conversion is due to unique genetic traits (38).  Such variations are relatively common and may explain up to 30% of the deviations in blood concentrations of omega-3 and omega-6 fatty acids among individuals (38,39).
  • Excessive intake of alcohol can interfere with the action of the converting enzymes (34,35,40,41).
  • Lack of nutritional factors that are necessary for the proper action of the enzymes (Vitamin B3, B6 and C;        and minerals such as zinc and magnesium) can depress the conversion of ALA to EPA and DHA (34,35,42,43).
  • Trans-fatty acids from fried foods and hydrogenated oils inhibit the reactions involved in the conversion of ALA to EPA and subsequently to DHA (10,34,35).
  • Variables such as smoking and the presence of chronic disease can inhibit the conversion of ALA to longer-chain omega-3 fatty acids (42).
  • Eating a low-fat or calorie-restricted diet can enhance conversion of ALA to EPA and DHA (42).
  • Eating turmeric seems to increase the conversion efficiency. Studies in rats show that combining intake of ALA with curcumin, one of the active ingredients in the spice turmeric, increases the DHA content of the brain and liver as well as the enzymes needed for the conversion of ALA into DHA (44).
  • The largest effect seems to come from the actual amount of omega-3s and omega-6s in the diet. When omega-6s are kept low, more long-chain omega-3s are produced, presumably because more of the conversion enzyme is available to make the conversion (45).  High intake of omega-6 fatty acids can reduce conversion by 40 to 60% (46).  Equal amounts of omega-3 and omega-6 fatty acids likely promote the highest conversion efficiency (42) although this situation is difficult to attain.  Omega-6:omega-3 ratios of 2:1 to 4:1 are achievable targets and offer conversion rates that are still excellent (13,47,48,49)


Boosting the production of EPA and DHA in your own body (13)

Though the above long list may make your head spin, it’s really not that difficult to encourage higher conversion of ALA to EPA and DHA.  Some of the factors that affect the conversion rate such as gender and genetics are beyond your control but there are many that you can influence.

Here’s what you can do…

Do not smoke, eat trans-fats or drink excessive amounts of alcohol.

Eat foods low in saturated fats.  Avoid added fats high in omega-6s.

Eat a diet made up of a wide variety of whole foods and be sure to include the nutritional powerhouses every day – leafy greens, cruciferous vegetables, legumes, brightly coloured fruits and vegetables and grains.  These foods will ensure that you optimize your intake of vitamins, minerals and phytochemicals that support the conversion enzymes.

Aim for a low-fat, predominantly plant-based diet.

Include ½ teaspoonful of turmeric in your daily food.

Most importantly, balance your omega-3 and omega-6 intake;

Make sure you eat foods high in ALA every day.  (Refer to the Plant-Sources of ALA list above.)

Studies suggest that if no direct sources of EPA and DHA are consumed, you should double the suggested daily adequate intake of ALA to provide sufficient raw materials for conversion (50,13).  This can be done through adding 1 tablespoonful of ground flaxseed or 1 ½ tablespoonsful of chia seeds to your diet every day.

NOTE:  Make sure you grind your flaxseeds before consuming.  Nutrients from whole flaxseeds are difficult to absorb.



Limit foods high in omega-6 fatty acids;

Plant-derived oils – corn oil, cottonseed oil, safflower oil, soybean oil, sunflower oil, walnut oil, sesame seed oil,

hempseed oil

Processed foods

Corn kernels

Eat high-fat foods low in omega-3s such as sunflower seeds, pumpkins seeds, sesame seeds and pine nuts in moderation.  However, note that it is possible to overconsume omega-3s.  Don’t be afraid to include some healthy high-fat whole plant foods in your diet (avocados, nuts and seeds).

Oil is completely unnecessary in cooking.  Stock, juice, wine or even plain water can substitute nicely for sautéing.  However, if you feel you must use a small amount, canola oil is your best choice with an omega-6:omega-3 ratio of 2:1.

Most fruits are fairly well-balanced in omega-3s and omega-6s.


 Should I take a supplement to ensure that I am getting enough long-chain omega-3s?

Though it is possible to optimize your conversion of ALA to the longer chain omega-3s, the myriad of factors affecting this reaction makes it difficult to tell if the result will be high enough levels of EPA and DHA for optimum brain health.  Some research in both humans and animals has demonstrated that DHA synthesized from ALA does indeed meet brain DHA requirements (33). Additionally, vegetarians do not show clinical signs of DHA deficiency (50) and rates of neurological disease in vegans and vegetarians are comparable to those of omnivores (32,33). Other research suggests that our bodies may have evolved to avoid the over-production of DHA since DHA is highly unsaturated and easily oxidized by free radicals which increases the possibility of disease (13).

Conversely, there is also evidence that many people are not obtaining enough long-chain omega-3s.  The human brain is 50% fat and people with cognitive impairment and dementia demonstrate lower levels of both EPA and DHA in their bloodstreams (51).  Research from 2013 followed 86 older adults with dementia and discovered that those starting out the study with higher levels of long-chain omega-3 levels experienced a slower rate of cognitive decline (52).  MRI scanning has shown that higher long-chain omega-3 levels in the bloodstream are associated with lower abnormalities and higher quality white matter in the brain (8).  In addition, higher EPA and DHA levels are linked to larger brain volume over time.  Normal aging shrinks the brain; high long-chain omega-3 blood levels may slow this loss.  A double-blind randomized interventional study from 2014 showed significant improvements in brain function and less brain shrinkage after 6 ½ months of supplementation with long-chain omega-3 fatty acids from fish oil (8).  It appears that having sufficient long-chain omega-3s may be very important for preserving brain health.

As you can see, research on the benefits of the long-chain omega-3s is conflicting.  It may be that if ALA intake is adequate in plant-based eaters, its conversion will be sufficient to meet health needs.  However, additional supplementation with long-chain omega-3s may confer extra health benefits (13).

Complicating matters further is the difficulty in determining just how efficient we are as individuals in converting ALA to longer-chain omega-3s.  Not all laboratories have the ability to perform the Omega-3 Index Test that measures omega-3 blood levels.  It is also problematic to quantitate the possible genetic differences in the amount and quality of our own individual enzymes that produce these omega-3s.  On the other hand, studies have confirmed that plant-based eaters low in EPA and DHA blood levels who take 250 mg daily of algae-derived DHA (or combined EPA and DHA) do increase their long-chain omega-3 blood levels to brain-healthy levels (53).


Putting this all together, our best bet seems to be the following (50,13);

Adopt a lifestyle and diet that will optimize your body’s conversion of ALA into EPA and DHA. (See above under “Boosting the Production of EPA and DHA in Your Own Body”.)

Add to this a supplement from an algae source containing 200 to 300 mg of preformed long-chain omega-3s on two or three days each week.  In this way you will allow your body to produce omega-3s by not depressing their production with a daily supplement but you will ensure that you have a back-up healthy source of long-chain omega-3 fatty acids.

If you find it is just not possible for you to follow the omega-3 production-boosting habits outlined above, then take your algae-derived DHA (or combined EPA/DHA) supplement of 250 mg every day.


Why are algae-derived omega-3 supplements recommended?

Fish do not manufacture EPA and DHA themselves.  It is the tiny ocean and freshwater organisms known as microalgae (phytoplankton) that create these longer chain omega-3s.  Fish benefit when they eat the algae and accumulate the omega-3 in their body tissues, in turn supplying us with EPA and DHA when we eat them (15).  However, as previously discussed, fish flesh also contains damaging heavy metals, chemicals and other pollutants.

Omega-3s derived from algae are an environmentally friendly and entirely renewable source.  The process takes place in controlled environments in tanks and results in a product that is free of contaminants and toxic pollutants (54). In addition, omega-3s from algae have higher bioavailability than omega-3s from krill oil or fish oil (55).  DHA from algae is also 100% bioequivalent to the DHA in fish flesh (56).  Research has shown that vegans respond robustly to a low dose supplement of 254 mg of long-chain omega-3 fatty acids from algae (53). Thus microalgae are an excellent non-animal source of these healthy fatty acids.


Special concerns (50,13)


Pregnant and lactating women have increased needs of DHA and EPA.  Sufficient omega-3 ingestion during pregnancy is necessary for the proper development of the brain and the retina of the fetus, as well as ensuring optimal pregnancy length for the best health of the child (57).  Canada’s Food Guide states that, during pregnancy, DHA is transferred from the mother to the baby’s growing brain and other tissues.  Nevertheless, they note that there is no evidence that women who don’t eat fish are at risk for pregnancy complications or poor child development (58).

It is likely prudent however that all pregnant and breastfeeding mothers, regardless of the type of diet they are eating, supplement with a source of long-chain omega-3 fatty acids and also reduce their consumption of omega-6-rich oils (58,59).  A daily supplement of 200 to 300 mg of DHA (or combined DHA/EPA) is recommended.  Infants should be breastfed for two years or more and, if breastfeeding is stopped early, a formula with added DHA should be chosen and DHA supplements started in the child at one year of age.

If a woman wishes to eat fish during pregnancy, she should choose a species lower in mercury (salmon, trout, herring, haddock, canned light tuna, pollock (Boston bluefish), sole, flounder, anchovy, char, hake, mullet, smelt, Atlantic mackerel and lake white fish) and consume only about 5 to 8 ounces a week.  Fish with higher mercury content (fresh/frozen tuna, shark, swordfish, escolar, marlin, and orange roughy) should be limited to no more than 5 ounces a month (58,).


Old Age/Chronic Diseases

Older people and those with chronic diseases may have reduced ability to convert ALA into DHA or EPA and are advised to take a daily supplement of 200 to 300 mg of DHA (or combined DHA/EPA) (42).




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My name is Debra Harley (BScPhm) and I welcome you to my retirement project, this website. Over the course of a life many lessons are learned, altering deeply-rooted ideas and creating new passions.

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