Abstract
Good sources of the long-chain n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) include cold-water fish and seafood; however, vegan diets (VGNs) do not include animal-origin foods. Typically, US omnivores obtain enough dietary EPA and DHA, but unless VGNs consume algal n-3 supplements, they rely on endogenous production of long-chain fatty acids. VGN diets have several possible concerns: (1) VGNs have high intakes of linoleic acid (LA) as compared to omnivore/non-vegetarian diets. (2) High intakes of LA competitively interfere with the endogenous conversion of alpha-linolenic acid (ALA) to EPA and DHA. (3) High somatic levels of LA/low ALA indicate a decreased ALA conversion to EPA and DHA. (4) Some, not all VGNs meet the Dietary Reference Intake Adequate Intake (DRI-AI) for dietary ALA and (5) VGN diets are high in fiber, which possibly interferes with fat absorption. Consequently, health professionals and Registered Dietitians/Registered Dietitian Nutritionists working with VGNs need specific essential fatty acid diet guidelines. The purpose of this review was: (1) to suggest that VGNs have a DRI-AI Special Consideration requirement for ALA and LA based on VGN dietary and biochemical indicators of status and (2) to provide suggestions to ensure that VGNs receive adequate intakes of LA and ALA.
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Key Points
The purpose of this review was to summarize relevant findings of studies on dietary intake and biological indicator status of LA, AA, ALA, EPA, and DHA in plasma, serum, erythrocytes, platelets, breastmilk, and adipose tissue in vegans (VGNs), and discuss the reasons why VGN diets may need DRI Special Consideration. The most abundant n-3 PUFA is ALA, which is found in plant-based oils and/or oil food sources like flaxseed (linseed), English walnut, hemp seed, and chia.
To summarize, the present DRI AI for essential fatty acids is intended for general healthy populations, and does not take into account groups with specific dietary needs/requirements. It is suggested that adult VGNs have separate AIs for LA and ALA than omnivores and utilize recommendations of between 2.2–4.4 g/g of ALA d (or 1.1 g/day/1000 Kcals). Additionally, a 4:1 n- 6:n-3 ratio could be considered for both VGNs and omnivores, since there are no present recommendations for an essential fatty acid ratio.
It is advisable for VGNs to decrease unnecessary or high sources of LA in the VGN diet, especially if they consume >10:1 ratio of n-6:n-3, and/or greater than the AI for LA. Decreasing high LA intake in VGNs could be an option; however, decreasing LA intake without being mindful of ALA dietary sources that are also high sources of LA might also decrease ALA intake.
Main Findings from This Review 1. Most studies indicate that VGNs consume higher amounts of LA compared to omnivores, with confirmation in tissues stores; however, there are inconsistent findings of AA tissue concentrations compared to omnivores; 2. There are inconsistent results of ALA intake by VGNs compared to omnivores; 3. Most studies show that VGNs consume low to zero amounts of EPA and DHA, unless they take supplements; 4. Most studies indicate that plasma, serum, erythrocytes, adipose, and platelet levels of EPA and DHA are lower in VGNs than omnivores; 5. VGNs may need an ALA increase of 2.2–4.4 g/day (or 1.1 g/day/1000 Kcals) depending on the amount of LA in the diet in order to achieve a 4:1 n-6:n-3 ratio, as well as a decrease of dietary LA if intake of LA is higher than recommended and 6. Special consideration recommendations for both ALA and LA for adult VGNs should be considered by the AI/DRI.