Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are endogenous lipids that are influenced by fasting and high-fat diets and linked to improved insulin sensitivity in mice. These compounds typically feature a chain of either 16 or 18 carbon atoms (for example, palmitoleic, palmitic, oleic, or stearic acid) esterified with a hydroxy fatty acid chain of similar length. One specific FAHFA, known as 5-OAHSA, consists of oleic acid bonded to the fifth carbon of hydroxy stearic acid. Within the FAHFA family, OAHSAs exhibit the highest serum levels in AG4OX mice, which are known for their glucose tolerance attributed to the overexpression of the Glut4 glucose transporter in adipose tissue.