Dietary Substitution with an a-Linolenic Acid—Rich Vegetable Oil Increases Eicosapentaenoic Acid Concentrations in Tissues.
Dietary Substitution with an a-Linolenic Acid—Rich Vegetable Oil Increases Eicosapentaenoic Acid Concentrations in Tissues.
Year: 1994
Authors: E Mantzioris, M J James, R A Gibson, L G Cleland.
Publication Name: Amer. J. Clin. Nutr.
Publication Details: Volume 59; Page 1304.
Abstract:
In a Western style diet, a high ratio of n-6 to n-3 PUFA exists which can result in an increase in the ratio of n-6 to n-3 eicosanoids. LA competes with ALA for synthesis into longer chain PUFAs and in high levels can be an antagonist to the production of n-3 eicosanoids. Increased concentrations of EPA in cell membranes have been shown to be beneficial in reducing CHD, hypertension, and inflammatory disorders. The authors indicate that in order for long-term dietary strategies for increasing cellular EPA concentrations to be successful, information regarding the relationships between cellular concentrations of EPA and dietary amounts of ALA and of LA is required. The objective of this study was to determine whether ALA from flaxseed oil could increase tissue EPA levels when fed as part of a normal diet in healthy humans. Thirty healthy male volunteers were randomly assigned into two dietary treatments for a 4 week period. The experimental group (n=15) consumed a high ALA diet (flaxseed oil) in the form of flaxseed oil and flaxseed-butter spread (butter to flaxseed ratio of 2:1). The flaxseed oil diet was comprised of 30% fat, 5% ALA and 3% LA. The control group (n=15) consumed their traditional diet (CON) and were instructed to avoid foods containing n-3 fatty acids. The CON diet was comprised of 30% fat, 0.4% ALA and 8% LA. Both groups maintained these diets for 4 weeks. Following this period, the diets of all subjects were supplemented with fish oil capsules (1.62 g EPA and 1.08 g DHA) for 4 weeks. The results established the effectiveness of altering the ratio of dietary LA:ALA in increasing EPA levels in plasma lipid fractions and cellular membranes. The flaxseed oil diet resulted in significant increases in ALA concentrations in plasma PL, cholesteryl ester, and TG fractions (eight-fold increase) and in neutrophil PLs (50% increase). EPA concentrations increased by 2.5-fold in the plasma lipid fractions and neutrophil PLs. After fish-oil supplementation, EPA concentrations increased in parallel in both dietary groups, remaining higher in the flaxseed oil group for both the plasma lipid fractions and neutrophil PLs. No increases in DHA levels were noted following the ALA rich diet. However, the authors suggest that a longer term feeding period may be necessary to allow for enhanced DHA synthesis. No changes were noted in serum TC or TG, observations that were not unexpected since the subjects were normolipidemic. Although EPA supplied in the form of encapsulated fish oil is an efficient means of increasing EPA levels, long term domestic use of flaxseed oil appears to be more feasible and would also lead to significant increases in tissue EPA. This finding has particular importance for individuals who do not consume fish or who follow strict vegetarian diets. The authors concluded that the substitution of ALA-rich flaxseed oil for commonly consumed cooking oils and spreads in traditional diets is an effective method to elevate tissue EPA concentrations to levels comparable with those associated with fish-oil supplementation.
