Why is carbon from some polyunsaturates extensively recycled into lipid synthesis?

AbstractWe summarize here the evidence indicating that carbon from α‐linolenate and linoleate is readily recycled into newly synthesized lipids. This pathway consumes the majority of these fatty acids that is not β‐oxidized as a fuel. Docosahexaenoate undergoes less β‐oxidation and carbon recycling than do α‐linolenate or linoleate, but is it still actively metabolized by this pathway? Among polyunsaturates, arachidonate appears to undergo the least β‐oxidation and carbon recycling, an observation that may help account for the resistance of brain membranes to loss of arachidonate during dietary deficiency of n−6 polyunsaturates. Preliminary evidence suggests that de novo lipid synthesis consumes carbon from α‐linolenate and linoleate in preference to palmitate, but this merits systematic study. Active β‐oxidation and carbon recycling of 18‐carbon polyunsaturates does not diminish the importance of being able to convert α‐linolenate and linoleate to long‐chain polyunsaturates but suggests that a broad perspective is required in studying the metabolism of polyunsaturates in general and α‐linolenate and linoleate in particular.