Bioavailability and Potential Uses of Vegetarian Sources of Omega-3 Fatty Acids: A Review of the Literature

Presently alpha linolenic acid (ALA) is the most widely used vegetarian LC3PUFA, but only marginal amounts are converted into eicosapentaenoic (EPA) and docosahexaenoic acid (DHA); both of which are strongly related to human health.  Currently, fish oils represent the most prominent dietary sources of EPA and DHA; however, these are unsuitable for vegetarians. Alternative sources include flaxseed, echium, walnut, and algal oil but their conversion to EPA and DHA must be considered. The present systematic review sets out to collate information from intervention studies examining the bioavailability of alternative vegetarian long chain omega-3 (n3) polyunsaturated fatty acids (LC3PUFA) sources. Ten key
papers published over the last 10 years were identified with seven intervention studies reporting that ALA from nut and seed oils was not converted to DHA at all. Three studies showed that ingestion of micro algae oil led to significant increases in blood erythrocyte and plasma DHA. Further work is now needed to identify optimal doses of alternative vegetarian LC3PUFAs and how these can be integrated within daily diets. The potential role of algal oils appears to be particularly promising and an area in which further research is warranted. (Authors abstract)

Research has identified that vegetarians/vegans, nonfish eaters and pregnant mothers may not consume adequate quantities of LC3PUFAs.   A vegan diet is completely devoid of DHA and vegetarian diets contain smaller amounts of DHA than that of meat and particularly fish eaters. Clinical studies suggest that tissue levels of LC3PUFA’s are at low levels in vegetarians and particularly low in vegans. Currently, the most significant vegetarian dietary form of n3 is ALA. Abundant ALA commodities include flaxseed, walnut, and echium seed oils .This paper provides an overview of the health effects of ALA and LCPUFA as well as the research on conversion aspects.

The authors acknowledge that diets with a high ratio of LA to ALA can suppress DHA synthesis in favor of docosapentenoic acid (DPA) which takes the place of DHA in the retinal and neural tissues. Various dietary and lifestyle factors can impair LCPUFA synthesis including high intakes of saturated, hydrogenated or “trans”-fatty acids, a lack of vitamin and mineral cofactors and lifestyle choices such as smoking and the use of alcohol and caffeine. Because of these dietary aspects, usually little ALA is converted to EPA and even less to DHA. 

The focus of the paper is to review the numerous health benefits of the LC3PUFAs including anti-inflammatory properties which have been used  successfully in the treatment of CVD, CHD, inflammatory diseases, eczema, psoriasis, and rheumatoid arthritis. The authors recommended a direct intake of EPA and DHA for optimal for CHD risk reduction.  A meta analysis of LC3PUFA’s and CHD completed concluded that dietary intakes of LC3PUFA’s reduce overall mortality, mortality due to myocardinal infarction and sudden death in patients with CHD.

A number of alternative sources of LC3PUFA are available.   ALA rich oils would be appropriate supplements for vegetarians and vegans.  Algae oils are a relatively recent innovation in the food industry.  Capable of providing large amounts of DHA algae are also the primary source of DHA in the food chain and are available for use in fortification of foods and infant formulas along with dietary supplements.  Algae oils provide a direct source of DHA so will (of course) be more effective than ALA sources at increasing body ;levels of DHA.

Non-fish sources of n3 are particularly important for vegetarians, non-fish eaters and pregnant mothers. Flaxseed oil is a rich source of n3 and has been proven to have good bioavailability
when used in bulk or emulsion in several studies. The authors conclude that interventions using algae oil have been extremely successful in terms of the safety and bioavailability of algal DHA. These are not however viable sources of n3 fatty acids for vegans, a point missed in the review. Also the authors do not give proper cried to the health benefits of plant based ALA. (Editors comments)