α‐linolenic acid interconversion is sufficient as a source of longer chain ω‐3 polyunsaturated fatty acids in humans: An opinion

Abstract

α-linolenic acid (αLNA) conversion into the functionally important ω-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), has been regarded as inadequate for meeting nutritional requirements for these PUFA. This view is based on findings of small αLNA supplementation trials and stable isotope tracer studies that have been interpreted as indicating human capacity for EPA and, in particular, DHA synthesis is limited. The purpose of this review is to re-evaluate this interpretation. Markedly differing study designs, inconsistent findings and lack of trial replication preclude robust consensus regarding the nutritional adequacy of αLNA as a source of EPC and DHA. The conclusion that αLNA conversion in humans is constrained is inaccurate because it presupposes the existence of an unspecified, higher level of metabolic activity. Since capacity for EPA and DHA synthesis is the product of evolution it may be argued that the levels of EPA and DHA it maintains are nutritionally appropriate. Dietary and supra-dietary EPA plus DHA intakes confer health benefits. Paradoxically, such health benefits are also found amongst vegetarians who do not consume EPA and DHA, and for whom αLNA conversion is the primary source of ω-3 PUFA. Since there are no reported adverse effects on health or cognitive development of diets that exclude EPA and DHA, their synthesis from αLNA appears to be nutritionally adequate. This is consistent with the dietary essentiality of αLNA and has implications for developing sustainable nutritional recommendations for ω-3 PUFA.

Supplementation with Flaxseed Oil Rich in Alpha-Linolenic Acid Improves Verbal Fluency in Healthy Older Adults

“…Comparatively, the conversion of ALA to DHA in the liver is reported to be inefficient [ 11 , 12 ], but the ALA intake, in this case taken daily, may have had a possible accumulative effect [ 38 ] and a small amount may have been sufficient [ 9 , 39 ]. This view is consistent with the consideration that DHA synthesis from ALA in humans is nutritionally adequate, despite the low rate of ALA-to-DHA conversion, as reported in a recent review [ 13 ]. Furthermore, in this exploratory study on various cognitive functions, ALA intake had no effect on anything other than the verbal fluency task.…”

“…ALA administration increases brain-derived neurotrophic factor (BDNF) and acts on neural elongation [ 9 , 10 ]. Although the efficiency of DHA synthesis is limited, the conversion rate of ALA to EPA in humans is approximately 0.1–21% of ingested ALA, and the conversion rate to DHA is 0.1–9% [ 11 , 12 ], and ALA can act similarly to DHA [ 13 ].…”

A review of recent studies on the enrichment of eggs and poultry meat with omega-3 polyunsaturated fatty acids: novel findings and unanswered questions

“… Burge (2022) opined that in humans, the limited synthesis of EPA and DHA from ALA could be the result of evolutionary pressures that ensured the production of adequate amounts of VLC n-3 PUFA to meet the body's normal physiological needs and avoid deficiency symptoms. While dietary and supra-dietary EPA plus DHA intakes confer health benefits, Burge (2022) argued that no adverse effects on health or cognitive development have been reported in humans whose diets exclude EPA and DHA, indicating that their synthesis from ALA appears to be nutritionally adequate. This could also be the case in chickens, which also have a limited ability to hepatically convert ALA or SDA to VLC n-3 PUFA but typically do not exhibit symptoms of essential fatty acid deficiency.…”

Docosahexaenoic Acid in Formulas for Term Infants: The Way from Pioneer Idea to Mandatory Dietary Recommendation

“…Docosahexaenoic acid (C22:6n-3, DHA) is the bioconversion product of complex biosynthetic mechanisms from the initial essential fatty acid (EFA), alpha-linolenic acid (C18:3n-3, ALA) [ 1 ]. While there is an ongoing discussion about whether ALA interconversion might be sufficient on its own to cover n-3 long-chain polyunsaturated fatty acid (LCPUFA) needs in humans [ 2 ], the utmost majority of n-3 LCPUFA supplementation trials in pregnancy, lactation, and infancy included preformed DHA [ 3 ]. Today, there are various DHA delivery systems applied to improve the bioavailability of DHA and support the role of its functionality [ 4 ].…”