Abstract
α-Linolenic acid (ALA) is an n-3 fatty acid found in plant-derived foods such as linseeds and linseed oil. Mammals can convert this essential fatty acid into longer-chain fatty acids including EPA, docosapentaenoic acid (DPA) and DHA. Women demonstrate greater increases in the EPA status after ALA supplementation than men, and a growing body of animal model research identifies mechanisms by which sex hormones such as oestrogen and progesterone interact with the synthesis of EPA and DHA. Alternatively, EPA, DPA and DHA can be consumed directly, with oily fish being a rich dietary source of these nutrients. However, current National Diet and Nutrition Data reveals a median oily fish intake of 0 g daily across all age ranges and in both sexes. As longer-chain n-3 fatty acids have a crucial role in fetal and neonatal brain development, advice to consume dietary ALA could prove to be a pragmatic and acceptable alternative to advice to consume fish during pregnancy, if benefits upon tissue composition and functional outcomes can be demonstrated. Further research is required to understand the effects of increasing dietary ALA during pregnancy, and will need to simultaneously address conflicts with current dietary advice to only eat ‘small amounts’ of vegetable oils during pregnancy. Improving our understanding of sex-specific differences in fatty acid metabolism and interactions with pregnancy has the potential to inform both personalised nutrition advice and public health policy.
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Key Points
Given that pregnancy induces increased Δ6 desaturase expression, most likely under the influence of increasing circulating progesterone, it would be anticipated that providing increased dietary ALA during pregnancy could enhance maternal endogenous DHA synthesis, sex hormones and n-3 fatty acid metabolism and thereby increase DHA availability to the fetus. Animal studies indicate that an ALA-rich diet can achieve brain DHA and immune organ EPA concentrations which are comparable with those obtained with provision of a salmon-oil-rich diet. This is suggestive of either specific transport of DHA, or fetal endogenous synthesis of DHA from ALA. Th author suggests that if an ALA-rich diet can be demonstrated to have comparable effects in human trials, it may be appropriate to revise dietary advice given to women during pregnancy to encourage increasing consumption of ALA. To date, human intervention studies have demonstrated that providing additional dietary ALA during pregnancy and lactation can significantly increase the erythrocyte EPA status of mothers and increase the DHA content of breast milk in early infancy and plasma EPA and umbilical vein and artery DPA concentrations status of neonates. ALA could therefore prove an important and acceptable dietary alternative to fish during pregnancy. Given that the majority of the UK population never consumes oily fish, it may be time to take a pragmatic approach to dietary recommendations for the general population and messaging targeted at pregnant women. Either fish oil capsules or provision of ALA may therefore prove to be acceptable alternatives to oily fish. Future research will also need to balance the potential effects of dietary ALA with likely interactions with age, genetic polymorphisms in FADS genes, BMI and smoking and use of hormone therapies such as the contraceptive pill and hormone-replacement therapy when considering other variables which may enhance or reduce the efficacy of targeted nutritional advice.