Re-evaluation of the 13C isotope fractionation associated with lipids biosynthesis by position-specific isotope analysis of plant fatty acids

•Fatty acids from C3 plants present a non-stochastic 13C intramolecular distribution.•This pattern is inherited from sugar and isotopic fractionation during biosynthesis.•Acetyl-CoA carboxylase-catalyzed reaction is associated with a 13C isotope effect.•Fatty acids 13C pattern could be preserved in n-alkanes through diagenesis.