Dietary α‐Linolenic Acid (ALA) is Sufficiently Converted to Docosahexaenoic Acid (DHA) to Increase Bioactive Lipids Derived from DHA
Authors: Leng Shan , Aukema Harold M. 
Published: November 2023

Background

There is considerable debate on whether α‐linolenic acid (ALA) can be sufficiently converted to docosahexaenoic acid (DHA) for optimal health. DHA has beneficial health effects and is critical for tissues such as the retina and brain. It produces bioactive lipids, such as resolvins, protectins and hydroxy DHA (HDoHE) with anti‐inflammatory, vasodilatory, anti‐aggregatory and anti‐proliferative effects. Many organizations worldwide provide recommendations for minimal DHA intake, but vegans, who consume little or no DHA, have shown no apparent detrimental health effects. Moreover, the Institute of Medicine Dietary Reference Intakes do not provide a minimum recommendation for DHA, and only have a recommendation for adequate ALA intake. Although dietary ALA generally does not significantly alter DHA levels, tissue fatty acid levels are not always an accurate indication of bioactive lipid levels. Therefore, the objective of this study was to determine whether dietary ALA can alter levels of DHA derived bioactive lipids (oxylipins) in normal rat tissues.

Methods

Weanling Sprague‐Dawley rats were provided diets based on the AIN93G diet. The isocaloric and isolipidic diets had oils (soy, olive, flax) containing adequate levels of ALA (0.3 g/100 g diet) or higher ALA (3.4 g/100 g diet), with ALA replacing monounsaturated fatty acids in the latter diet. Male and female rats were provided the diets ad libitum for 6 weeks, after which livers, kidneys and serum were collected for oxylipin analysis. Phospholipid fatty acids were purified from lipid extracts using TLC and quantified as fatty acid methyl esters by GLC. Oxylipins were extracted in methanolic solutions containing deuterated internal standards. After solid phase extraction, lipidomic analysis of >150 oxylipins was performed by HPLC/MS/MS, and those above the limit of quantification (LOQ) were quantified using the stable isotope dilution method. Approximately 100 oxylipins above the LOQ were detected in each of the 3 tissues.

Results

Consistent with many prior studies, providing a higher ALA diet resulted in higher phospholipid ALA and eicosapentaenoic acid (EPA) in all 3 tissues, and DHA concentrations were only higher in liver, but not in the kidney or serum. Providing higher dietary ALA also resulted in higher levels of all ALA derived oxylipins detected, and most of the EPA derived oxylipins in all 3 tissues. With respect to DHA oxylipins, however, despite not altering DHA levels, in the kidney 12 DHA oxylipins were (~20–100%) higher in rats provided high ALA. Similarly in serum, 9 DHA oxylipins were (~20–100%) higher in rats provided high ALA. In liver, despite differences in DHA, only 2 oxylipins derived from this fatty acid were altered by dietary ALA level.

Conclusions

These results illustrate that although dietary ALA may not alter tissue DHA concentrations, it does increase the levels of many oxylipins derived from DHA in kidney and serum. This indicates that the conversion from ALA to DHA is sufficient to increase production of DHA derived bioactive lipids in these tissues. These findings may have implications for dietary recommendations of n‐3 fatty acids.

Support or Funding Information

Natural Sciences and Engineering Research Council of Canada (NSERC)