Cyclopropane fatty acids (CPFAs), such as dihydrosterculic acid (DHSA), are secondary fatty acids of microbial origin recently identified in foods and human plasma. Their plasmatic concentration is suggested to be affected by consumption of CPFA-rich foods, especially dairy products. However, very little is known about the occurrence of CPFAs in human tissues and their nutritional value. This preliminary screening aims to investigate the presence of CPFAs in breastmilk obtained from lactating Spanish women following a free-living diet by performing the GC–MS method previously applied for CPFA determination in dairy products. For the first time, DHSA was detected in human breast milk fat (at about 0.4 mg/ 100 mL breastmilk), supporting the importance of better understanding its occurrence in vivo that may be related to the dietary habits followed by the lactating mother. Future studies are needed to determine its biological role both in adults and infants, who would be exposed to this CPFA during the breastfeeding.

Pilar Gómez-Cortés gratefully acknowledges the Spanish Ministry of Science and Innovation for the Ramón y Cajal research contract (RYC2019-027933-I).

Peer reviewed