It’s pretty much common knowledge by now that consumption of fish oil provides a wide range of health-related benefits. These benefits extend to almost every organ system imaginable and include the prevention of numerous disease states. There is even some evidence that fish oil aids in fat loss, helping to keep you lean by simply replacing other fats in the diet on a calorie-for-calorie basis (8). The body of research showing positive effects is so compelling that it seems almost too good to be true.
The benefits of fish oil can be traced to two compounds: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Rather than bore you with technical details as to their mechanisms of action, I’ll just say that EPA and DHA regulate various genes in the body, particularly those involved in inflammatory processes and energy metabolism. The fat in certain fish species act as a storehouse of “preformed” EPA and DHA that is readily used by the human body after consumption. You can obtain these compounds by eating various cold water fish species (such as salmon, mackerel, and sardines), or by consuming fish oil supplements in either liquid or capsule form. Simple enough.
Some people, however, are averse to consuming fish and their oils. Vegetarians, in particular, fall into this category. Others simply don’t care for the taste of fish and find that supplements don’t digest well. So the question then arises whether a vegetable source is available that provides the same benefits as fish oil.
Flaxseed oil is often touted as a vegetable-based alternative to fish oil. Unlike fish oil, flax does not contain preformed EPA or DHA. Rather, it possesses a compound called alpha-linolenic acid (ALA) that can be converted to EPA and DHA in the body. This is where things start to get murky…
In order for conversion of ALA to take place, it must undergo a complex process that further “desaturates” the fatty acid and correspondingly forms longer chain polyunsaturated derivatives. Problem is, research shows that this conversion process is rather inefficient. A review article by Canadian researchers Mélanie Plourde and Stephen Cunnane (7) estimated that only 5% of ALA is converted to EPA and that less than 0.5% of ALA is converted to DHA.
With respect to EPA, the news is not as bad as it sounds. A recent study by Dr. Gwendolyn Barceló-Coblijn (3) and colleagues showed that consumption of 2.4 grams of flax oil increased EPA levels in red blood cells by 1.4-fold — an amount comparable to supplementation with 0.6 grams of fish oil (although less than that found with supplementation of 1.2 grams of fish oil). Similarly, a group of researchers at Emory University led by Dr. Charles Harper (5) found that supplementing with 3 grams of ALA derived from flax oil increased blood levels of EPA by 60%. However, neither study noted any changes in blood levels of DHA. This is significant in that DHA appears to be the more biologically important of the two. DHA is believed to be particularly necessary for brain function, as well as eye health. So the fact that ALA is poorly converted to DHA seemingly makes flax oil a poor substitute for fish oil.
Now before drawing any final conclusions on the matter, a couple of things need to be considered. First, none of the studies evaluated the subject’s consumption of omega-6 fats. Why is this relevant? Well, omega-6 fats compete with omega-3s for desaturation. If there is an abundance of omega-6s in the diet, then conversion of omega-3s will be reduced. And in the Western world, the average ratio of omega-6 to omega-3 is well in excess of 20:1! Thus, it’s possible that if you reduce the ratio to a more palatable 4:1, a greater DHA conversion would be seen.
What’s more, the studies in question looked at the levels of DHA in the plasma and red blood cells — not in specific tissues that require DHA. It is possible that tissues such as the brain, retina, and kidneys use ALA to manufacture DHA as needed, and this would not show up in tests of the blood.
What’s more, it is quite possible that ALA may confer other benefits over and above those found in EPA and DHA. Multiple studies have shown that consumption of ALA itself has cardioprotective effects (2, 4, 6). Further, as noted in the study by Barceló-Coblijn (3), ALA antagonizes the synthesis of arachidonic acid, which is a pro-inflammatory that can negatively impact the body. This alone may possibly aid in preventing various disease states.
Moreover, flax oil contains compounds called lignans that are not present in fish oil. Lignans have been shown to possess antioxidant properties and produce anti-estrogenic effects that may provide a host of additional health-related benefits, including a reduced risk of various cancers (1).
Bottom line: At this point it seems that fish oil probably contains unique properties that are not obtainable in flax. Therefore, until research shows otherwise, flax oil should not be considered a substitute for fish oil. However, flax may provide additional benefits over and above those found in fish oil, and could have an additive effect when the two are consumed in combination.
1. Adolphe JL, Whiting SJ, Juurlink BH, Thorpe LU, Alcorn J. Health effects with consumption of the flax lignan secoisolariciresinol diglucoside. Br J Nutr. :1-10.
2. Ascherio A, Rimm EB, Giovannucci EL, Spiegelman D, Stampfer M, Willett WC. Dietary fat and risk of coronary heart disease in men: cohort follow up study in the United States. BMJ1996;313:84–90.
3. Barceló-Coblijn G, Murphy EJ, Othman R, Moghadasian MH, Kashour T, Friel JK. Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid. Am J Clin Nutr. 2008 Sep;88(3):801-9.
4. de Lorgeril M, Renaud S, Mamelle N, et al. Mediterranean alpha-linoleic acid-rich diet in secondary prevention of coronary heart disease. Lancet 1994;343:1454–9.
5. Harper CR, Edwards MJ, DeFilippis 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.
6. Hu FB, Stampfer MJ, Manson JE, et al. Dietary intake of alpha-linoleic acid and risk of fatal ischemic heart disease among women. Am J Clin Nutr1999;69:890–7.
7. Plourde M, Cunnane SC. Extremely limited synthesis of long chain polyunsaturates in adults: implications for their dietary essentiality and use as supplements. Appl Physiol Nutr Metab. 2007 Aug;32(4):619-34
8. Schoenfeld, B. (2004) Omega-3 Fatty Acids: A Novel Fat Burner. Strength and Conditioning Journal, 26(3), 72–76