Bioavailability of Alpha-Linolenic Acid in Subjects after Ingestion of Three Different Forms of Flaxseed

January 1, 2008 Human Health and Nutrition Data 0 Comments

Bioavailability of Alpha-Linolenic Acid in Subjects after Ingestion of Three Different Forms of Flaxseed

Year: 2008
Authors: Austria, J.A. Richard, M.N. Chahine, M.N. Edel, A.L. Malcolmson, L.J. Dupasquier, C.M.C. Pierce, G.N.
Publication Name: Journal of the American College of Nutrition
Publication Details: Volume 27; Number 2; Pages 214 – 221.


Dietary flaxseed may have significant health-related benefits due to its high content of the omega-3 fatty acid, alpha-linolenic acid (ALA). However, before extensive work can be undertaken in clinical populations to determine its efficacy, basic information on ALA bioavailability from flaxseed and the physiological effects of its ingestion need to be examined. The purpose of this study, therefore, was to determine the bioavailability of ALA when the flaxseed was ingested in the form of whole seed, milled seed or as flaxseed oil.The flaxseed components (30 g of seed or 6g of ALA in the oil) were baked into muffins for delivery over a 3 month test period in healthy male and female subjects. Flaxseed ingestion over a 1 month period resulted in significant (P= 0.005) increases in plasma ALA levels in the flaxseed oil and the milled flaxseed supplemented groups. The former group had significantly (P= 0.004) higher ALA levels than the milled flaxseed group. The subjects supplemented with whole flaxseed did not achieve a significant (P> 0.05) increase in plasma ALA levels. An additional two months of  flaxseed ingestion did not achieve significantly higher levels of plasma ALA in any of the groups. However, no significant increase was detected in plasma eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) levels in any of the flax-fed groups. There were no changes in plasma cholesterol or triglycerides or in platelet aggregation at any time point in any of the groups. Subjects in all of the groups exhibited some symptoms of gastro-intestinal discomfort during the early stages of the study but these disappeared in the oil and milled seed groups. However, compliance was a problem in the whole flaxseed group. In summary, ingestion of flax oil and milled flaxseed delivered significant levels of ALA to the plasma whereas whole flaxseed did not. Whole seed and oil preparations induced adverse gastrointestinal effects within 4 weeks and these were severe enough to induce the withdrawal of some subjects from these two groups. No one withdrew from the group that ingested milled flaxseed and, therefore, may represent a good form of flaxseed to avoid serious side-effects and still provide significant increases in ALA to the body. (Authors abstract)
Relatively little is known about the form of flaxseed that should be used to insure the effective efficient delivery of ALA. In most studies, ground flaxseed is used because it is thought that it is the most effective means by which to achieve ALA bioavailability. However, this remains to be tested. The purpose of the present investigation, therefore, was to examine the bioavailability of ALA when delivered in the diet in different kinds of flaxseed. The authors hypothesize that plasma ALA levels will be significantly elevated in subjects administered flax oil, ground flaxseed and whole flaxseed, but greater in subjects fed ground flaxseed compared to those fed whole flaxseed. It is also hypothesized that flax oil will deliver ALA in greater amounts to the circulation than either seed variety. It was also hypothesized that all three groups will have a diminished capacity for platelet aggregation over the course of this study, and that gastrointestinal complications will be reduced in subjects administered ground flaxseed and flaxseed oil in comparison to the whole seed. None of the forms of flaxseed delivered in this study altered the circulating cholesterol or triglyceride levels. The duration of the study (12 weeks) may not have been sufficient to detect changes as well. All forms of flaxseed induced some gastro-intestinal discomfort. However, as hypothesized, the whole seed group experienced more serious side-effects.  Oil appears to be the most optimal mode for the delivery of ALA. However, its very short shelf half-life makes it difficult to use in commercial nutritional products for the public. Ground flaxseed, alternatively, appears to be a viable middle option. Ground flaxseed will deliver ALA well enough to elicit a >3 fold increase in ALA levels, will have a better shelf half-life than the oil, and will deliver other important components of flaxseed including fiber and lignans that also may have health benefits and are not present in the oil. None of the modes of flaxseed delivery induced changes in platelet aggregation. This is in contrast to DHA and EPA that induce an inhibition of blood clotting. This lengthening of bleeding times by the fish omega-3 fatty acids can be viewed as both a positive and negative effect depending upon the clinical circumstances. Inhibition of blood clotting is thought to be a positive effect in cardiovascular health where clots are thought to play an important role in ischemic heart disease and stroke. However, longer bleeding times are undesirable in surgical theatres. The lack of effect of flaxseed on this parameter will, therefore, not be a cause for concern in future clinical studies using flaxseed. The levels of EPA and DHA did not change during the course of this study despite large increases in ALA levels in the plasma in two of the groups. However, the authors note that ALA has been shown to induce quantitatively different but qualitatively similar effects as fish oil PUFAs on many parameters of cardiovascular health. (Editors comments)

Back to Databases

Affiliated Organizations

Flax Focus Newsletter

Stay up-to-date with important flax news and announcements with our FLAX FOCUS newsletter.