Application of new methods and analytical approaches to research on polyunsaturated fatty acid homeostasis

New methods and analytical approaches are important to challenge and/or validate established beliefs in any field including the metabolism of polyunsaturated fatty acids (PUFA; polyunsaturates). Four methods that have recently been applied toward obtaining a better understanding of the homeostasis of PUFA include the following: whole‐body fatty acid balance analysis, magnetic resonance imaging (MRI), 13 C nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). Whole‐boby balance studies permit the measurement of both the percentage of oxidation of linoleate and α‐linolenate and their conversion to long‐chain PUFA. This method has shown that β‐oxidation to CO 2 is normally the predominant metabolic fate of linoleate and α‐linolenate. Furthermore, models of experimental undernutrition in both humans and animals show that β‐oxidation of linoleate and α‐linolenate markedly exceeds their intake, despite theoretically sufficient intake of linoleate or α‐linolenate. Preliminary results suggest that by using MRI to measure body fat content, indirect whole‐body linoleate balance can be done in living humans, 13 C NMR spectroscopy provided unexpected evidence that linoleate and α‐linolenate were metabolized into lipids synthesized de novo , an observation later quantified by tracer mass balance done using GC‐C‐IRMS. This latter method showed that within 48 h of dosing with 13 C‐α‐linolenate, >80% underwent β‐oxidation to CO 2 by suckling rats, whereas 8–9% was converted to newly synthesized lipids and <1% to docosahexaenoate. Further application of these recently developed methods in different models should clarify the emerging importance of β‐oxidation and carbon recycling in PUFA homeostasis in mammals including humans.