Plant-Sourced Omega-3 Fatty Acids
Seeds of the flax plant are our richest commercial source of plant-based omega-3
fatty acids. (See the page on this website concerning Essential Fatty Acids for more
information.) The parent of the omega-3 family of fatty acids is alpha-linolenic
acid (ALA), the omega-3 prominent in flaxseed oil. [For science-minded readers,
let it be said that ALA is a polyunsaturated 18-carbon fatty acid with 3 double bonds]
What is meant by calling ALA the "parent" compound of the omega-3 family? ALA can
be converted by enzymes in the bodies of animals into the longer omega-3 fatty acids,
including:
- EPA (eicosapentaenoic acid) – 20 carbons with 5 double bonds
- DHA (docosahexaenoic acid) – 22 carbons with 6 double bonds
Conversion of ALA into EPA and DHA
There has been much controversy and negative advertising around the issue of how
much ALA is actually converted by the body into EPA and DHA. Both human beings and
herbivorous animals have tissue enzymes which can facilitate that conversion. And
these same enzymes are involved in the conversion of the omega-6 fatty acid linoleic
acid (LA) into arachidonic acid, the omega-6 used by tissues to make pro-inflammatory
local hormones.
Unfortunately, modern Western lifestyle and eating habits interfere with the human
conversion enzymes. What lifestyle and dietary factors can interfere with the
conversion of ALA into EPA and DHA? Here are some of the major interfering factors:
- High intake of the omega-6 LA relative to ALA preoccupies the conversion enzymes with converting LA into arachidonic acid so that ALA conversion is impaired.
- Trans-fatty acids (found in hydrogenated vegetable oils in shortenings, deep fat fried foods, and processed foods) cripple the conversion enzymes irreparably. Tissues have to manufacture brand new enzymes to replace those damaged by trans-fats.
- Insulin excess in the bloodstream (from sugar and refined starch abuse) impairs enzyme function. High insulin levels are the key feature of Syndrome X (Metabolic Syndrome) now believed to be a precursor to type 2 diabetes.
- Alcohol abuse poisons conversion enzymes.
- Deficiency of nutrient co-factors that support function of conversion enzymes --- vitamins B3, B6, and C, plus minerals zinc and magnesium.
How much dietary ALA do our tissues convert into EPA and DHA?
Conversion rates vary by gender, age, and genetic factors. It seems that female
hormones (estrogens) support the activity of the conversion enzymes. For this reason,
women of reproductive years, who naturally would have the highest levels of estrogens
in any population, tend to be more efficient in the conversion of ALA. This is
understandable due to the need to provide adequate amounts of EPA and DHA for a fetus
in utero or for a nursing infant.
Due to these physiologic factors and the lifestyle factors, human conversion of ALA
into EPA ranges from 8% to 21%. Conversion of ALA into DHA ranges from 1% to 9%. What
do these conversion rates and percentages really mean in terms of how ALA we consume
forms recommended doses of ALA’s most abundant commercial source, flaxseed oil?
The recommended daily dose for flaxseed oil is one tablespoon (three teaspoons) for
every 100 pounds of body weight. (Many people do not realize that it takes fourteen
1,000 mg capsules to equal one tablespoon.) As a rule of thumb, we need to remember
that the recommended intake of combined EPA / DHA for general cardiovascular health
maintenance is 1,000 mg daily. This level of EPA / DHA is in accordance with the
frequently-cited GISSI studies in Italy of the daily intake amount of EPA / DHA
necessary to prevent a second heart attack. Let’s apply the conversion rates to
conservative estimates of the amount of ALA found in flaxseed oil.
ALA constitutes between 50% and 60% of the fatty acid content of flaxseed oil.
Depending on how much lignan and other fiber compounds are allowed to remain in the
extracted oil, the ALA content of one tablespoon (14,000 mg) of flaxseed oil can
vary, in conservative round figures, from 6000 mg to 7000 mg.
Based on their superior conversion ability, for women of reproductive age, each
tablespoon of flaxseed oil provides:
- 21% conversion of 6000 mg ALA --> 1260 mg EPA
- 4% conversion of 6000 mg ALA --> 240 mg DHA
- TOTAL per tablespoon flaxseed oil: 700 mg combined EPA/DHA.
Although this total EPA / DHA is less than the recommended 1000 mg, the recommended
daily dose of flaxseed oil is one tablespoon per 100 pounds of body weight. Thus, the
average man is going be taking something on the order of two tablespoons daily. And
that amount of flaxseed oil can be converted into protective quantities of EPA and DHA.
It must be emphasized that few if any of the studies took into account the dietary
and lifestyle factors discussed above that interfere with converting enzymes. By
getting these adverse factors under control in our daily habits, we can expect to get
even better conversion of ALA into EPA and DHA.