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News - Conversion of dietary ALA to EPA and DHA may be increased in non-fish eaters

By Dr Pieris Nicols PhD BSc (Hons) DipION

A new British study on the body’s conversion of the plant-based omega-3 alpha-linolenic acid (ALA) into the marine-based omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may offer hope for non-fish eaters. 

There are three main types of omega-3 fatty acids. The first one is ALA, which is abundant in certain plant foods, such as flax seeds, hemp seeds, walnuts, and their oils. It is also found in leafy vegetables and some animal fat, especially from grass-fed animals. ALA is classed as an “essential fatty acid.” That means the body needs ALA for numerous body functions, but cannot make it from scratch. It must therefore be obtained through the diet. ALA has direct health benefits, through its role in managing inflammation and may be protective of the heart against arrhythmia (irregular heart beat). 

The other two main types of omega-3 fatty acids are EPA and DHA, also known as long-chain omega-3 fatty acids. They are found mainly in marine sources such as the fatty tissues of cold-water oily fish, and algae. EPA and DHA have been associated with a wide range of health benefits, including improved blood triglyceride and cholesterol levels, heart rate, blood pressure in hypertensive patients, blood vessel function, and reduced risk of cardiovascular disease and stroke. They may also have a protective effect against a number of disorders including cancer, autoimmune diseases like lupus and rheumatoid arthritis, age-related macular degeneration, and inflammatory conditions. 

What about vegans, vegetarians and those who simply cannot stand fish? How do they obtain EPA and DHA?

It has long been known, through studies carried out in adult humans, that the body partially converts ALA into other omega-3 fatty acids, including EPA and DHA. That is why ALA is known as the parent of all the omega-3 fatty acids. However, according to current scientific reviews, the proportion of ALA converted to EPA is very low, and conversion to DHA is less clear. There are gender differences in conversion. Conversion is substantially greater in women of childbearing age than in healthy men of a similar age. However, the story could also be different in non-fish eaters. 

A UK research group, led by Dr Ailsa Welch at the University of East Anglia, estimated dietary intakes and blood levels of ALA, EPA and DHA among 4,902 fish-eaters and non-fish-eating meat-eaters, vegetarians or vegans. Surprisingly, despite the significantly lower intakes of EPA and DHA among non-fish-eaters, their blood levels of EPA and DHA were much more similar to those of regular fish eaters. The researchers estimated the conversion of ALA into EPA and DHA by calculating the ratio of long-chain omega-3 fatty acids to plant-derived dietary ALA. This ratio was significantly greater in all the non-fish-eating groups than in the fish eaters, suggesting that in non-fish-eaters the body may compensate for the lack of EPA and DHA by boosting its conversion of ALA from plant foods. 

The researchers commented: “The implications of this study are that, if conversion of plant-based sources of n-3 PUFAs were found to occur in intervention studies, and were sufficient to maintain health, it could have significant consequences for public health recommendations and for preservation of the wild fish supply.” 

The results of this study were reported in The American Journal of Clinical Nutrition.

Article References

Welch AA, Shakya-Shrestha S, Lentjes MA et al. Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the precursor-product ratio of -linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort. Am J Clin Nutr 2010; 92:1040-51.

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