Abstract Long-chain polyunsaturated fatty acids (LC-PUFAs) are critical for infant growth and development, particularly arachidonic acid (ARA, C20:4n-6) and docosahexaenoic acid (DHA, C22:6n-3). ARA and DHA are components of cell membrane phospholipids and play an important role in cell division, differentiation, and signaling; and DHA is the n-3 fatty acid predominant in the developing brain and retina. During the third trimester of pregnancy, LC-PUFAs increase substantially in fetal circulation, and a “biomagnification” process in the fetal brain is observed. Moreover, LC-PUFAs are precursors of eicosanoids and metabolites, which modulate the intensity and duration of the immune response. LC-PUFA synthesis implies complex desaturation and elongation processes on their principal precursors, linoleic acid (LA) (18:3 n-6) (series n-6) and α-linolenic acid (LNA) (20:3 n-3) (series n-3), where fatty acid desaturases (FADS) and elongases (ELOVL) are competing. It is important to notice that during the first months of life, as a consequence of low enzymatic activity, LC-PUFA synthesis from LA and LNA is reduced, especially in those infants carrying variations in the FADS and ELOVL genes, which are involved in LC-PUFA synthesis, and so they are unable to supply their own DHA and ARA needs. Homozygote infants for FADS haplotype A (97 % of the Latinoamerican population) show low levels of ARA (only 43 %) and DHA (only 24 %) when compared to those carrying haplotype D (more prevalent in Europe, Africa and Asia). Human milk is the only source of LA, LNA, ARA, and DHA for the neonate and infant till complementary feeding (CF) is introduced. Infants fed with infant formulas must receive enough amounts of LA, LNA, ARA, and DHA to cover their nutritional requirements. The new guidelines by the European Food Safety Authority (EFSA) (2016) recommend that infant formulas and follow-on formulas must contain 20-50 mg of DHA/100 kcal (0.5-1 % of total fatty acids, which is higher than in human milk and the majority of infant formulas in the market), and it is not necessary to add ARA. This new regulation, which is already applicable since February 2020, has resulted in profound controversy because there is no scientific evidence about its appropriateness and safety for healthy children. Then, different international expert groups have revised the research already published about the effects of ARA and DHA addition to infant formulas, and discussed different emerging questions from this European directive. The expert group led from the University of Granada (Spain) recommends the addition of ARA in similar or higher concentrations than those of DHA, at least equal to those present in human milk (0.3 % of total fatty acids), although preferably 0.5 % and up to around 0.64 % of total fatty acids, since new studies confirm the optimal intake of ARA and DHA during the different developmental stages. This recommendation could be of particular importance for infants carrying the haplotype A of FADS.
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