Fatty acid esters of hydroxy fatty acids and alkyl-diacylglycerols: minor but bioactive components in human milk

Abstract As the optimal source of nutrition for infants, investigations into the human milk lipidome have been quite extensive. Much of the work, however, has been focused on major lipid components such as triglycerides, possibly undermining its actual complexity. This review focuses on two minor but bioactive lipid classes in human milk: fatty acid esters of hydroxy fatty acids (FAHFAs) and alkyl-diacylglycerols (TG(O)s). FAHFAs are known to exhibit anti-diabetic and anti-inflammatory effects, while TG(O)s are important for the prevention of childhood obesity. With the knowledge that early nutrition and metabolic health influence the risk of metabolic dysfunctions later in life, a comprehensive understanding of FAHFAs and TG(O)s, along with reliable characterisations in human milk, would better allow for the development of accurate human milk fat substitutes. This could have future implications as alternative or preventive treatments for infants with early markers of metabolic dysfunction, including diabetes and obesity. The structural characteristics, pathways for biosynthesis and degradation, bioactivity, dietary sources, and characterisations of FAHFAs and TG(O)s in human milk are discussed. Their statuses as emerging lipid classes, however, is reflected in the incomplete understanding of their biochemical pathways. Characterisations of FAHFAs and TG(O)s in human milk are relatively poor, and contradicting results are reported. This review also addresses the challenges involved in the study of minor lipids in complex biological matrices, and the possible reasons underlying the slower evolution of our understanding of FAHFAs and TG(O)s in human milk and their associations with health outcomes.