Marine omega-3s seen topping the vegetal-type omega-3 found in flax oil for preventive heart health
by Craig Weatherby and Randy Hartnell
By now, many people know that omega-3s are essential to optimal heart health and child development.
And the scientific hypothesis that dietary omega-3s inhibit cancer growth is supported by substantial evidence from animal and cell studies, as two well-respected researchers confirmed in a Vital Choices report published late last month (see “Media Reports Miss Fatal Flaws in New Review of Omega-3/Cancer Evidence”).
But Mr. Platkin raised a question of critical importance to consumers concerned about preventive health: “…is there a difference between the omega-3s in fish and those in walnuts?”
As Debra Palmer Keenan, a nutrition professor at New Jersey’s Rutgers University, told Platkin, "They are not the same thing … we have to stop talking about omega-3s and talk about DHA and EPA [marine omega-3s] and ALA [the main vegetal omega-3] as separate fatty acids.”
The omega-3 bait-and-switch
The results of a flood of research published in recent years confirms the heart-health benefits of marine omega-3s, and the corresponding negative consequences of the nation’s dire omega-3 deficiency.
Because these findings appeared widely in the media, it’s no surprise that major and minor manufacturers alike have rushed to lure consumers by adding omega-3s to their processed and packaged foods.
However, omega-3 fatty acids come in two forms, with distinctly different levels of preventive heart-health benefits:
- Marine Omega-3s (EPA and DHA): These long-chain omega-3s are found only in fish and algae. DHA is a key constituent of cell membranes, especially in the brain and eyes. Both are considered valuable for preventive heart health, but DHA is more important than EPA.
- Vegetal Omega-3 (ALA): This short-chain omega-3 is found in nuts, seeds, and the oils extracted from them. Common sources include soy oil, canola oil, and—by far the richest source—flaxseed oil. The body converts ALA into the two long-chain marine omega-3s EPA and DHA—mostly EPA—as well as a marine omega-3 called DPA that has no established health benefits.
Virtually all of the studies that showed omega-3s help protect against heart attacks and strokes employed fish or fish oil, which contain EPA and DHA, but no ALA.
As the experts quoted in Platkin’s article said, it’s far preferable that manufacturers fortify foods with marine omega-3s rather than plant-derived omega-3 fat
Yet, as we noted last August in an article titled “Beware the Omega-3 Bait-and-Switch”, most food manufacturers who’ve jumped on the omega-3 bandwagon fortify their foods with flaxseed oil.
Manufacturers engage in this seedy bait-and-switch because flax oil is cheaper than fish oil, and because fish oil becomes even more expensive when treated to eliminate its fishy flavor.
We’ll explain the reasons why medical experts prefer marine omega-3s in further detail below.
For starters, while flax oil consists of about 54 percent omega-3 ALA, most of the remaining 46 percent consists of the pro-inflammatory omega-6 fat called LA (linoleic acid), which Americans over-consume already. This omega-6 fat also elbows omega-3s out of the pathways that lead to incorporation into cell membranes, where omega-3s exert most of their beneficial effects.
Fish versus flax: evidentiary imbalance impairs comparisons
We searched the medical literature for information on the differences between marine omega-3s (EPA and DHA) and the vegetal omega-3 ALA found in flax oil.
Compared with marine omega-3s (EPA and DHA), there is not nearly as much good evidence regarding the effects of dietary ALA on the risk of cardiovascular disease, or its impact on risk factors like blood levels of cholesterol, insulin, sugar, inflammation, clotting factor, and triglycerides, and inflammation levels in arterial tissues.
As a German researcher put it in a 2003 review article, “Plant-derived alpha-linolenic acid [ALA] has been studied in a limited number of investigations. So far, some epidemiologic and a few mechanistic studies suggest a potential of protection from cardiovascular disease, but this potential remains to be proven in intervention [clinical] studies. In contrast… [EPA and DHA]… have been studied in thousands of investigations.”
His conclusion was affirmed in a review published late last year by researchers at Georgia’s Emory University, who said, “… the evidence suggests a role for fish oil … or fish in secondary [heart attack/stroke] prevention because recent clinical trial data have demonstrated a significant reduction in total mortality, coronary heart disease death, and sudden death. The data on ALA have been limited by studies of smaller sample size and limited quality.”
The scarcity of evidence aside, it’s very clear that on a cellular level, marine omega-3 fatty acids—especially DHA—enjoy the best evidence of cardiovascular benefit.
DHA seen as key to fish oil’s heart-healthy effects
Fish and fish oil have been proven to reduce deaths from cardiovascular health, thanks to their omega-3 fatty acids, EPA and DHA.
But, while EPA helps reduce dangerous tendencies toward unnecessary blood clotting (platelet aggregation), DHA appears to be the most important omega-3 for cardiovascular health, overall.
As the Japanese academics who authored a 2003 review article said, “…recent studies strongly suggest that DHA has more potent and beneficial effects than EPA.”
And in 2005, English researchers published findings that echo the Japanese scientists’ evaluation. As the Britons concluded, “…fish-oil produced predictable [and favorable] changes in… [blood levels of] …lipids [fats] and small, dense LDL (sdLDL) [“bad” cholesterol] that were not reproduced by the ALA-enriched diet. Membrane DHA levels appeared to be an important determinant of these fish-oil-induced effects.”
Dietary flax oil yields little bodily DHA
As we’ll detail below, ALA (usually from flax oil) appears to confer some cardiovascular benefits. However, marine omega-3s hold a clear edge. This is not surprising, for two reasons:
- Inflammation is considered a key factor in promotion of arterial plaque and the plaque ruptures and resulting blood clots that often constitute the direct cause of heart attacks and strokes. Both of the main marine omega-3s (EPA and DHA) are more effective than ALA at raising production of anti-inflammatory prostaglandins (ephemeral, hormone-like messenger chemicals).
- The findings of several recent studies suggest that while the omega-3 ALA in dietary flax oil can raise body levels of EPA, it does little to raise blood or heart tissue levels of DHA, especially in men.
The second point is supported by findings from a series of recent human and animal studies:
- The authors of the American Heart Association’s annual Scientific Statement on Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease for 2002 came to this conclusion: “Although some -linolenic acid [ALA] is converted to the longer-chain omega-3 fatty acids, the extent of this conversion is modest [0.02 to 15 percent] and controversial… [with conversion to] DHA …much less than that to EPA.”
- The standard American diet—high in saturated and omega-6 fats—puts a low ceiling on the rate at which the body converts ALA to marine omega-3s. Conversion of ALA to EPA drops to six percent and conversion of ALA to DHA dips below four percent when diets are high in saturated fats. And these regrettably low conversion rates drop by 40-50 percent when the diet is high in omega-6 fats.
- Healthy young British women who took supplemental flax oil containing 700 mg of ALA saw their blood levels of EPA rise by 21 percent and their DHA levels rise by only nine percent. As the researchers noted, “Comparison with previous studies suggests that women may possess a greater capacity for ALNA [ALA] conversion [to EPA and DHA] than men. Such metabolic capacity may be important for meeting the demands of the fetus and neonate [newborn infant] for DHA during pregnancy and lactation [nursing].” Renowned British fatty acid researcher Philip Calder attributes this gender advantage to the effects of estrogen.
- When African-American men and women with chronic heart disease took three grams [3,000 mg] per day of supplemental ALA (in flax oil capsules) it raised their average blood levels of EPA by 60 percent but had no effect on blood levels of DHA.
- How can we explain the large rise in EPA levels, which was many times that seen in all other ALA-to-EPA conversion studies? This African-American study group probably had extremely low tissue levels of EPA to begin with. We would expect such a scarcity of bodily EPA to result from the dietary pattern—high in fried foods and saturated fats, and low in seafood and plant sources of omega-3s—typical of African-Americans: a pattern that helps explain the high rates of cardiovascular disease and diabetes that afflict this population group.
- Rats that receive supplemental flax oil enjoy increased brain levels of DHA, and increased levels of EPA and DPA in their hearts and livers. However, supplemental flax oil does not raise DHA levels in their heart or liver tissues. In contrast, rats fed fish oil show increased DHA levels in their brains, hearts, and livers. And, compared with supplemental flax oil, fish oil does a better job of reducing rats’ tissue levels of arachidonic acid (AA): an essential but pro-inflammatory omega-6 fatty acid, high levels of which raise the risk of heart disease.
- Among young dogs given either ALA or marine omega-3s, those getting marine omega-3s enjoyed higher rises in blood levels of DHA, and larger beneficial effects on a key measure of visual capacity (retinal rod sensitivity).
Heartening facts about flax
Clearly, flax oil is no match for fish oil when it comes to preventing adverse cardiovascular events, but the picture is not entirely one-sided.
Dr. Daniel Mozaffarian of Harvard’s School of Public Heath—who we heard speak at last year’s Seafood & Health conference—reviewed the evidence and came to this conclusion in a 2005 review article: “Although clinical benefits have not been seen consistently in all studies, most prospective observational studies suggest that ALA intake reduces the incidence of CHD [coronary heart disease]…”
This may be because the ALA in flax oil appears to exert some of the anti-arrhythmic effects that make fish oils so effective at preventing sudden cardiac death. A recent analysis of data from the famed Nurses’ Health Study found that women who consumed the highest levels of ALA had a 38-40 percent smaller risk of sudden cardiac death: a correlation that persisted even among women reporting relatively high intakes of marine omega-3s.
And, like marine omega-3s, the ALA in flax oil and other seed oils is pretty effective at preventing dietary omega-6 fats forming pro-inflammatory arachidonic acid in cell membranes: a recognized risk factor for cardiovascular disease.
In conclusion, it seems fair to say that while flax oil is definitely heart-healthy, the marine omega-3s in fish and fish oil impart a much stronger preventive impact.
- Platkin C. What can omega-3 fatty acids do for you? Maybe a lot. Accessed online at http://www.globegazette.com/articles/2005/11/30/feature/doc438ce439b0026273183115.txt
- Hirafuji M, Machida T, Hamaue N, Minami M. Cardiovascular protective effects of n-3 polyunsaturated fatty acids with special emphasis on docosahexaenoic acid. J Pharmacol Sci. 2003 Aug;92(4):308-16. Review.
- Calder PC. n-3 Fatty acids and cardiovascular disease: evidence explained and mechanisms explored. Clin Sci (Lond). 2004 Jul;107(1):1-11. Review.
- von Schacky C. The role of omega-3 fatty acids in cardiovascular disease. Curr Atheroscler Rep. 2003 Mar;5(2):139-45. Review.
- Wendland E, Farmer A, Glasziou P, Neil A. Effect of alpha linolenic acid on cardiovascular risk markers: a systematic review. Heart. 2006 Feb;92(2):166-9. Epub 2005 May 12. Review.
- Finnegan YE, Minihane AM, Leigh-Firbank EC, Kew S, Meijer GW, Muggli R, Calder PC, Williams CM. Plant- and marine-derived n-3 polyunsaturated fatty acids have differential effects on fasting and postprandial blood lipid concentrations and on the susceptibility of LDL to oxidative modification in moderately hyperlipidemic subjects. Am J Clin Nutr. 2003 Apr;77(4):783-95.
- Harper CR, Jacobson TA. Usefulness of omega-3 fatty acids and the prevention of coronary heart disease. Am J Cardiol. 2005 Dec 1;96(11):1521-9. Epub 2005 Oct 21.
- Harper CR, Edwards MJ, Defilipis AP, Jacobson TA. Flaxseed Oil Increases the Plasma Concentrations of Cardioprotective (n-3) Fatty Acids in Humans. J Nutr. 2006 Jan;136(1):83-7.
- Barcelo-Coblijn G, Collison LW, Jolly CA, Murphy EJ. Dietary alpha-linolenic acid increases brain but not heart and liver docosahexaenoic acid levels. Lipids. 2005 Aug;40(8):787-98.
- Burdge GC, Wootton SA. Conversion of alpha-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women. Br J Nutr. 2002 Oct;88(4):411-20.
- Brenna JT. Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man. Curr Opin Clin Nutr Metab Care. 2002 Mar;5(2):127-32. Review.
- Gerster H. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? Int J Vitam Nutr Res. 1998;68(3):159-73. Review.
- Burdge GC, Calder PC. Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reprod Nutr Dev. 2005 Sep-Oct;45(5):581-97. Review.
- De Lorgeril M, Salen P. Use and misuse of dietary fatty acids for the prevention and treatment of coronary heart disease. Reprod Nutr Dev. 2004 May-Jun;44(3):283-8. Review.
- Albert CM, Oh K, Whang W, Manson JE, Chae CU, Stampfer MJ, Willett WC, Hu FB. Dietary alpha-linolenic acid intake and risk of sudden cardiac death and coronary heart disease. Circulation. 2005 Nov 22;112(21):3232-8.
- Mozaffarian D. Does alpha-linolenic acid intake reduce the risk of coronary heart disease? A review of the evidence. Altern Ther Health Med. 2005 May-Jun;11(3):24-30; quiz 31, 79. Review.
- Penny M. Kris-Etherton, PhD, RD; William S. Harris, PhD; Lawrence J. Appel, MD, MPH, for the Nutrition Committee. American Heart Association Scientific Statement: Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease. Circulation. 2002;106:2747.
- Wilkinson P, Leach C, Ah-Sing EE, Hussain N, Miller GJ, Millward DJ, Griffin BA. Influence of alpha-linolenic acid and fish-oil on markers of cardiovascular risk in subjects with an atherogenic lipoprotein phenotype. Atherosclerosis. 2005 Jul;181(1):115-24.
- Francois CA, Connor SL, Bolewicz LC, Connor WE. Supplementing lactating women with flaxseed oil does not increase docosahexaenoic acid in their milk. Am J Clin Nutr. 2003 Jan;77(1):226-33. Erratum in: Am J Clin Nutr. 2003 Oct;78(4):806.
- Heinemann KM, Waldron MK, Bigley KE, Lees GE, Bauer JE. Long-chain (n-3) polyunsaturated fatty acids are more efficient than alpha-linolenic acid in improving electroretinogram responses of puppies exposed during gestation, lactation, and weaning. J Nutr. 2005 Aug;135(8):1960-6.