Bioavailability of alpha-linolenic acid in subjects after ingestion of three different forms of flaxseed.

Background: 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.

Objective: 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.

Design: The flaxseed components (30 g of seed or 6 g of ALA in the oil) were baked into muffins for delivery over a 3 month test period in healthy male and female subjects.

Results: 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.

Conclusion: 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.