If you think back to the type of diet humans evolved to eat (cave-man diet), it provided a much more balanced mix of n-3 and n-6 fatty acids. Over the last century, modern diets have come to rely heavily on fats derived from vegetable oils (n-6) – bringing the ratio of n-6 to n-3 fatty acids from the cave-man’s ratio of 1:1 to the modern-day range of 20-30:1 – yikes! The unbalanced intake of high n-6 fatty acids and low n-3 fatty acids sets the stage for increases in blood viscosity (and tendency of blood to clot), vasoconstriction (and elevated blood pressure) and inflammatory processes (involved in everything from heart health to pain levels).
Fatty acids of the n-3 variety, however, have opposing biological effects to the n-6 fatty acids – meaning that a higher intake of n-3 oils can deliver anti-inflammatory, anti-thrombotic and vasodilatory effects that can lead to benefits in terms of heart disease, hypertension, diabetes, and a wide variety of inflammatory conditions such as rheumatoid arthritis and ulcerative colitis.
In the body, linoleic acid (n-6) is metabolized in the body to arachidonic acid – a precursor to specific “bad” eicosanoids which can promote vasoconstriction and elevated blood pressure. Linolenic acid (n-3), however, is metabolized in the body to EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). EPA serves as the precursor to prostaglandin E3, which may have vasodilatory properties on blood vessels – effects which can counteract the vasoconstriction caused by n-6 fatty acids. DHA has been associated with optimal brain development in infants.
Recent studies have shown consumption of linolenic acid and other n-3 fatty acids to offer protection against heart disease and heart attacks. This effect is thought to be mediated through the synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Fish oils contains large amounts of both EPA and DHA and the majority of studies in this area have used various concentrations of fish oil supplements to demonstrate the health benefits of these essential fatty acids. For example, one gram of menhaden oil (a common source) provides about 300 mg of these fatty acids. EPA is known to induce an antithrombotic (clot-preventing) effect through its inhibition of platelet cyclooxygenase (which converts arachidonic acid to thromboxane A2) and the “less-sticky” platelets that result. Fish oil, and its high content of EPA and DHA, may also protect against heart disease through an anti-inflammatory effect (via reduced cytokine production and/or increased nitric oxide production in the endothelium).
Consumption of broiled or baked fish, 2 or more times per week, is associated with a 40% reduction in risk of rheumatoid arthritis. In one study, 8 weeks of omega-3 supplementation (9-10 grams per day) resulted in significant improvements in joint pain and stiffness among arthritis sufferers.
Flaxseed, a rich plant source of omega-3 fatty acids, has been shown to lower both systolic and diastolic blood pressure (1-2 tablespoons daily). Epidemiological studies have shown that subjects with high intakes of linolenic acid (n-3) have been shown to have a 50% reduced risk of heart disease - which may be partly due to beneficial effects on blood pressure, cholesterol levels, blood clotting and heart rhythm. Indeed, omega-3 fatty acids are known to reduce thromboxane activity, which could explain the benefits of omega-3’s in reducing platelet aggregation (blood clotting) and blood vessel constriction.
There is also some evidence that omega-3 fatty acids from fish oil and flaxseed may help improve insulin sensitivity, modulate lipid metabolism and combat both mild depression and Attention Deficit and Hyperactivity Disorder (ADHD). Although the data is far from clear, it is known that omega-3 fatty acids are concentrated in the brain and that children and adults suffering from depression and/or ADHD typically show sub-optimal blood levels of essential fatty acids. In addition, population studies suggest that a high consumption of fish (rich in omega-3’s) may be related to a lower risk of depression, including postpartum depression. Mothers pass large amounts of essential fatty acids to their babies during the last 3 months of fetal brain development and via breast milk – so much that new mothers have only half the normal blood levels of omega-3 fatty acids and nursing mothers may have even lower levels.
A recent expert scientific advisory board at the National Institutes of Health highlighted the importance of a balanced intake of n-6 and n-3 fatty acids to reduce the adverse effects of elevated arachidonic acid (a metabolic product of n-6 metabolism). The committee recommended a reduction in the intake of n-6 fatty acids (linoleic acid) and an increase in n-3 (linolenic acid, DHA, EPA) intake. Adequate intake recommendations were established for the first time for the support of cardiovascular health in adults and brain development in infants (see dosage recommendations below).
No serious adverse side effects should be expected from regular consumption of essential fatty acid supplements – whether from fish oil or other common oil supplements (see below). Due to the tendency of n-3 fatty acids to reduce platelet aggregation (“thin” the blood), increase bleeding times can occur in some individuals.
The most common supplemental sources of essential fatty acids are fish oil – a good source of the omega-3 fatty acids. Other oils, such as flaxseed, borage seed and evening primrose are rich sources of essential fatty acids – but typically do not provide the high levels of concentrated EPA/DHA found in many fish oil supplements. The highest quality fish oil supplements should provide 18%-30% EPA and 12%-20% DHA. The higher the EPA/DHA content, the better (but also more expensive).
The best dietary sources of omega-3 fatty acids are fish such as trout, tuna, salmon, mackerel, herring, and sardines, which all contain about 1-2 grams of n-3 oils per 3-4 ounce serving. A minimum of 4-5 grams of linoleic acid (but no more than 6-7 grams) and 2-3 grams of linolenic acid are recommended per day. Supplements of linoleic acid (n-6) are typically not needed, whereas linolenic acid (n-3) supplements (4-10g/d) and/or concentrated EPA/DHA supplements (400-1000mg/d) are recommended to support cardiovascular health. Total DHA/EPA intake should approach about 1 gram per day – evenly split between the two. Pregnant and lactating women are advised to increase their DHA intake somewhat so that they consume at least 300 mg of DHA daily to ensure adequate brain development in their growing babies. When using flax as a concentrated source of essential fatty acids, a typical dose is 1-2 tablespoons per day.
“Vegetarian” Sources of EFAs
Source ALA Linolenic Gamma Oleic
Flax 45 15 0 39
Hemp 20 60 3 13
Black 13 52 17 10
Borage 1 37 23 16
Olive 0 10 0 71
Evening 0 68 9 8