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Fish
Oil versus Flax Seed Oil—Which Is Better?
2 March 2007
by Wyn Snow, Managing Editor
For strict vegans, the answer is clear: flax seed oil. For the rest of
us, there are pros and cons on both sides.
Benefits of eating fish
Numerous authorities tout the health benefits of eating fish, especially
fatty species which are rich sources of omega-3 fatty acids. Proven benefits
range from lowering triglycerides and blood pressure and the risk of heart
disease, to the more subtle effects of reducing chronic inflammation.
Some researchers are convinced that chronic inflammation at the cellular
level is the underlying cause of most of today’s significant diseases,
including diabetes and cancer as well as heart disease, high blood pressure,
and strokes. Dr. Barry Sears of “Zone Diet” fame would add osteoarthritis
and Alzheimer’s disease to that list.
Obtaining optimal levels of omega-3s, which are abundant in fatty fish,
is especially important for children and women of childbearing years. Omega-3s
are vital for brain development. Low levels during pregnancy and childhood
can have detectable negative impacts on intelligence.
Risks of eating fish
Concerns have grown during the past several decades about toxic contaminants
in fish. Recommendations from experts vary about how much fish to eat. Some
claim that the benefits outweigh the risks. However, the FDA’s official
advice is to eat fish twice a week, but not more often. This limit is especially
important for young children and women who are pregnant or may become pregnant,
because these toxins can impair neurological development.
Contaminants in fish can include mercury, other heavy metals including
arsenic, industrial byproducts such as dioxins, industrial compounds such
as PCBs, and pesticides such as DDT. Levels of various contaminants vary
by species, by locale, and whether the fish are wild or farmed.
For example, mercury is lowest in salmon and highest in swordfish (see
table below). In recent years, farmed salmon has been shown to
contain more toxic chemicals than wild salmon, largely because of contaminants
in the foods they are given. While some suppliers are taking steps
to improve salmon farming conditions, it is not clear how widespread
these changes are in the industry.
| Average Mercury Concentration in
Various Fish and Shellfish |
| |
| Fish/Shellfish |
 |
(parts per million) |
| |
|
|
| Swordfish |
|
0.97 |
| Albacore tuna |
|
0.35 |
| American lobster |
|
0.31 |
| Chunk light tuna |
|
0.12 |
| Cod |
|
0.11 |
| Pollock |
|
0.06 |
| Catfish |
|
0.05 |
| Salmon |
|
0.01 |
| |
|
|
| Source: Northeast States for Coordinated
Air Use Management; Food and Drug Administration. |
How the body deals with contaminants
The human body can and does rid itself of contaminants. However, the process
is slow for fat-soluble pollutants—which most of these are. It takes
more than one year for mercury levels to drop significantly. For some pollutants,
it can take as much as ten years to reduce the load by half. Typically,
our intake rates of these substances are higher than our ability to get
rid of them, so levels build up.
As many as 8% of US women of childbearing age have high mercury levels,
which means approximately 300,000 babies born each year are at risk for
various cognitive problems. Also, breast milk is one of the avenues the
body uses to rid itself of organic pollutants. Women who breastfeed can
transfer high levels of these chemicals to their infants along with the
nutrition. Therefore, women who are breastfeeding or plan to do so need
to be especially careful to minimize their exposure to mercury and other
contaminants.
As a result of all these concerns, many people wonder: Is fish oil safe?
And if so, is it safer to consume than fish itself?
Fish oil safety
Many omega-3 fish oil supplements do not contain these troublesome contaminants—as
evidenced by ConsumerLab.com, Consumer Reports, and other independent testing
organizations. However, some products have been found to be contaminated,
especially from countries whose production standards are not rigorous.
If you are concerned about the quality of your favorite brand of fish oil,
Dr. Barry Sears recently described a simple “toothpick poke test” that
may reassure you. Puncture several capsules with a needle or pin, and squeeze
the contents into a small cup-shaped container, such as a thimble. Set the
thimble (or other container) in the freezer for 5 hours. If you can easily
push the toothpick into the oil, Sears says that means it does not contain
serious levels of contamination.
Another strategy is to look for quality seals on the label. Both the NSF
and NNFA quality seals (shown at right) mean that the product does not contain
heavy metals. Specifically, any lead, mercury, arsenic, cadmium and/or chromium
that might be present must be at levels below the standards set by the World
Health Organization. In order to quality for the NSF and NNFA quality seals,
any claims on the label that the product does not contain other contaminants
must be supported by independent laboratory tests. Also, supplement products
consisting of 2% oil or more must pass two tests for the presence of oxidation
and rancidity.
Some manufacturer labels that do not have these quality seals do claim
their product does not contain PCBs, mercury, lead, or various other contaminants.
They should have reports from independent, third-party labs that verify
this claim. You can ask to see a copy of these reports. If they refuse to
supply this documentation, you can complain to the Federal Trade Commission
(FTC)—which is charged with making sure that companies have evidence
to support their marketing claims.
Given these concerns about the quality of fish oils, many consumers are
wondering whether they should continue taking fish oil or rely instead on
flax seed oil.
Is fish oil “better” than flax seed oil?
In one respect, fish oil is definitely “better” than flax seed
oil. Fish oil contains two omega-3s that are especially important: EPA and
DHA. The body uses EPA to create many hormone-like substances that reduce
inflammation and other “excited” states in the body, such as
raised blood pressure. Also, eight percent of the brain is composed of EPA
and DHA, and one wants to be sure this 8% stays healthy!
Taking fish oil can guarantee that the body gets enough of these two vital
omega-3s.
However, Dr. Udo Erasmus, author of Fats that Heal,
Fats that Kill, claims
that the process manufacturers use to produce most vegetable cooking oils—a
process often used to remove contaminants from fish oils as well—is
itself destructive to the quality of the oil. According to Erasmus, oils
that have undergone this refining, bleaching and deodorizing process “contain
0.5 to 1.0% damaged, highly toxic molecules.” On the other hand, Erasmus
manufactures and sells a competing product, so such statements may be convenient
marketing claims rather than independently verified scientific fact.
If you want to avoid oils that have been exposed to this refining, bleaching,
and deodorizing process, look for either cold-pressed or unrefined on a
product’s label. Both terms mean that a mechanical process was used
to extract the oil rather than chemicals.
Benefits of flax oil
Flax seed oil contains an omega-3 called alpha-linolenic acid (ALA), which
is one of two fatty acids that the body needs and cannot make for itself.
Several other sources of ALA do exist, most notably walnuts and hemp seed.
Omega-3s are needed by every cell in the body. Among other things, an ample
supply helps ensure that cell membranes stay flexible so that cells can
get nutrients easily.
The body can use ALA to make all the other omega-3 fatty acids that it
needs, including both EPA and DHA. Thus, if you get enough ALA, you don’t
need to eat any other sources of omega-3s.
Another advantage of getting one’s omega-3s from the ALA in flax
oil is that the body does not create more EPA and DHA than it needs. Therefore,
ingesting too much EPA/DHA is not an issue.
The human body uses a variety of omega-3s, not just EPA and DHA. To make
the full range of these omega-3s, the body needs ALA from flax oil (or walnuts
or other sources) in addition to EPA and DHA. Thus, one needs to consume
some ALA even if fish and/or fish oil are plentiful in one’s diet.
Is flax oil “better” than fish oil?
Since one needs ALA anyway, and the body can make all the other omega-3s
it needs from ALA, does that mean flax seed oil is a better source than
fish oil for one’s omega-3s? Not necessarily.
The body uses various enzymes to convert ALA to other omega-3s, and the
process is not very efficient, especially as one gets older. Estimates of
the rate of conversion range from 5% to 25%. In order to make sufficient
amounts of EPA and DHA, one needs to consume 5 or 6 times more ALA than
if one relies on fish oil alone. Also, women convert ALA to the other omega-3s
more efficiently than men, largely so they can meet the nutritional demands
of their infants during pregnancy and breastfeeding.
Another consideration is that ALA competes metabolically with the other
essential fatty acid that the body cannot make for itself. Linoleic acid
(LA) plays the same role for omega-6 fatty acids that ALA does for omega-3s:
The body uses LA to make all the other omega-6s that it needs. (To understand
the difference between an omega-3 and omega-6 fatty acid, see our article
Chemical and Physical Structure
of Fatty Acids.)
By competes, we mean that when LA is oversupplied in the diet, the body
makes more of the LA-derived fatty acids than it needs, and not enough of
the ALA-derived ones. The “LA side” of these substances help
us react to dangers and stress and are therefore crucial to our health and
survival, but when they are oversupplied, the result is chronic high blood
pressure, cellular inflammation, and other conditions leading to today’s
panoply of degenerative diseases.
Unfortunately, the recent emphasis on vegetable oils has led to a 10:1
ratio between LA and ALA in the American diet. While there is no consensus
yet on what an optimal ratio would be, estimates range from 4:1 to 2:1.
Consuming smaller amounts of the omega-6 LA helps the body maintain a healthy
balance between the “stimulating” LA substances and the “calming” ALA
substances. One excellent method of improving this ratio is switching to
monounsaturated oils like olive oil. While canola oil does contain some
ALA, it also contains a higher level of LA, so is not a recommended method
of improving one’s LA-to-ALA ratio.
How much do we need?
For healthy adults, the recommendation is 300-500 mg per day of EPA and
DHA combined, plus an additional 800 to 1100 mg of ALA.
The EPA/DHA recommendation can usually be met with one softgel capsule
of fish oil (with 1 gram or 1000 mg of fish oil) which usually contains
180 mg of EPA and 120 mg of DHA, totalling 300 mg of the two omega-3s. However,
amounts do vary (some products are stronger, some weaker), so look at the
amounts of EPA and DHA provided, and add them together to see if the product
supplies 300 mg in one serving.
Dr. Barry Sears further recommends that people with diabetes, osteoarthritis,
and heart disease take twice that amount of fish oil. He also recommends
that people with cancer take four times that amount. However, people with
congestive heart failure should not be taking large quantities of fish oil,
see toxicity discussion below.
While cod liver oil is a potent source of EPA/DHA, containing as much as
1000-1200 mg in one tablespoon, it is also a concentrated source of vitamins
A and D. Both vitamins A and D are fat-soluble, and become toxic at high
dosage levels. As noted earlier in this article, the body does not easily
rid itself of fat-soluble substances, so prudence is called for.
For vegans and other health-conscious consumers, another option is vegetarian
DHA supplements derived from algae oil. Fish get their DHA by feeding on
algae.
Flax seed oil contains 8 grams (8000 mg) of ALA per tablespoon.
| ALA Content of Selected Foods |
| |
| Food |
|
ALA (grams) |
| |
| Flaxseed oil, 1 Tbsp. |
|
8.0 |
| Hempseed oil, 1 Tbsp. |
|
2.7 |
| Canola oil, 1 Tbsp. |
|
1.6 |
| Soybean oil, 1 Tbsp. |
|
1.0 |
| |
|
|
| Walnuts, 1 oz. |
|
2.7 |
| Flaxseeds, 1 Tbsp. |
|
2.6 |
| Soybeans, 1 cup cooked |
|
1.1 |
| Leafy greens, 1 cup raw |
|
0.1 |
| Wheat germ, 2 Tbsp. |
|
0.1 |
Are there any toxicity concerns?
Ingesting too much of anything—including water!—can cause problems.
Medline recommends that “Patients taking more than 3 grams of omega-3
fatty acids from supplements should do so only under a physician’s
care.”
Concerning the potential impact of high dosages, the National Institutes
of Health (NIH) say:
“Very large intakes of fish oil/omega-3 fatty acids (‘Eskimo’ amounts)
may increase the risk of hemorrhagic (bleeding) stroke. High
doses have also been associated with nosebleed and blood in the urine.
Fish oils appear to decrease platelet aggregation and prolong bleeding
time, increase fibrinolysis (breaking down of blood clots), and may reduce
von Willebrand factor.”
As for the impact on type II diabetes, research indicates that taking fish
oil might result in a slight increase to fasting blood glucose
levels, and/or a slight decrease to blood sugar levels—presumably
during the day! Thus, people taking insulin or other drugs for diabetes
should be supervised by their doctor when changing their intake of fish
oil or ALA.
People with congestive heart failure—or any other condition
where the heart is receiving insufficient blood flow—should consult
with their doctor and be cautious about consuming omega-3 fatty acids. In
congestive heart failure, according to Wikipedia, “Cells that are
only barely receiving enough blood flow become hyperexcitable,” which
can lead to irregular heartbeats and sudden cardiac death.
It appears that omega-3s stabilize heart rhythm by removing these hyperexcitable
cells from functioning. This is beneficial for people with plenty of heart
cells to spare, but in congestive heart failure, removing hyperexcited cells
can mean the heart no longer pumps enough blood for the patient to survive.
In conclusion
Both fish oil and flax seed oil have benefits and potential drawbacks.
Fish oil is an excellent and usually uncontaminated source of EPA and DHA,
which the body uses to make the “calming” omega-3 fatty acids
and keep the brain healthy. Consuming them directly can ensure that one
gets enough. Flax seed oil contains ALA, which the body can use to make
all the omega-3s that it needs. The body needs ALA to make other omega-3s,
even when it gets enough EPA and DHA from fish or fish oils.
As for drawbacks, some fish oil products are contaminated, and even those
that are not may have undergone a cleaning process that creates a small
percentage of toxic molecules. On the other hand, getting all one’s
omega-3s from flax oil means that one needs to consume significantly more.
Also, it is possible to ingest too much omega-3s, even though the greater
health risk is of consuming too much omega-6 LA. Also, people with congestive
heart failure should take omega-3s only with the full knowledge and active
supervision of their physician.
In conclusion, why limit oneself to either/or when it’s better to
have both/and? Eating a modest amount of fish or fish oil (or algae-based
DHA supplements) ensures a direct supply of EPA and DHA, while adding flax
seed oil to one’s diet ensures a healthy intake level of ALA. Every
cell in your body will thank you for it.
A physician comments on the fish oil–flax seed
oil debate
Epidemiologic evidence has pointed to the cardiovascular
benefits of fish and fish oil for a very long time [1], gaining
momentum in the 1970s with the observation that Greenland
Inuits, with a very high omega-3 intake and very high fat
diets had a very low risk of cardiovascular disease, but
it was not until the large and well-conducted Italian GISSI
Prevenzione [2] trial in 1999 which showed that a very modest
1gm supplementation of EPA & DHA significantly reduced
mortality in post-heart attack patients that the medical
establishment took widespread notice of fish oil.
As far
as I know, there is no similar evidence base in favor of
flax seed oil. Therefore, I would have a hard time saying
that flax seed has nearly as much to offer as fish oil.
We can extrapolate and theorize that flax seed oil should
confer a similar benefit, based on its (much lower) omega-3
content, enough to recommend it as an alternative to fish
oil for strict vegans, but I would call it clearly second
best.
The reference to fish oil lowering von Willebrand factor
[vWF] is probably correct, based on the 1987 study at Brown
[3] which showed that vWF was significantly lowered by fish
oil in type-1 diabetics, who as a group are at increased
risk for stroke and heart attack, possibly because of increased
vWF, which is known to be increased in first-time ischemic
stroke victims, regardless of diabetes, and is a marker of
endothelial stress. Perhaps more significantly, triglycerides,
which are associated with cardiovascular disease, and which
are notoriously elevated in type-2 diabetics, are lowered
by fish oil. (This is the only FDA-approved indication for
fish-oil, in the form of the eight to ten times more expensive
prescription extract Omacor, for treating severe hypertriglyceridemia.)
While bleeding times are slightly increased and platelet
activity is decreased by fish oil, there are no demonstrated
adverse health outcomes linked to this bleeding. A much more
potent anti-platelet drug, low-dose aspirin, increases bleeding
much more, but is taken by millions of people with an elevated
risk of cardiovascular disease because it is proven to significantly
lower overall risk, including that associated with bleeding.
Dr. Peter Everett is a founder of the Dietary Supplement
Quality Initiative, sponsor of supplementquality.com
References:
1. Kromhout D, Bosschieter EB, de Lezenne Coulander C. The
inverse relation between fish consumption and 20-year mortality
from coronary heart disease. N Engl
J Med, 1985 May 9;312(19):1205-9.
2. Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto
miocardico. Dietary supplementation with n-3 polyunsaturated
fatty acids and vitamin E after myocardial infarction: results
of the GISSI-Prevenzione trial. Lancet, 1999 Aug 7;354(9177):447-55.
3. Miller ME, Anagnostou AA, Ley B, Marshall P, Steiner
M. Effect of fish oil concentrates on hemorheological and
hemostatic aspects of diabetes mellitus: a preliminary study.
Thromb Res, 1987 Jul 15;47(2):201-14.
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