Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are a class of endogenous lipids whose levels are modulated by fasting and high-fat diets and are linked to insulin sensitivity. These compounds typically consist of a C-16 or C-18 fatty acid, such as palmitoleic, palmitic, oleic, or stearic acid, esterified to a hydroxylated C-16 or C-18 lipid. One specific form of FAHFA, known as 9-OAHSA, involves the esterification of oleic acid to 9-hydroxy stearic acid. Within the FAHFA family, OAHSAs notably represent the predominant form found in the serum of glucose-tolerant AG4OX mice, which uniquely overexpress the Glut4 glucose transporter in adipose tissue.