Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are newly identified endogenous lipids regulated by fasting and high-fat feeding and associated with insulin sensitivity in mice.¹ Structurally, these esters are comprised of a C-16 or C-18 fatty acid (e.g., palmitoleic, palmitic, oleic, or stearic acid) linked to either a C-16 or C-18 hydroxy substituent. 12-POHSA is a FAHFA consisting of palmitoleic acid esterified at the 12th carbon of stearic acid. The levels of POHSA are significantly elevated in serum of glucose tolerant AG4OX mice, which overexpress the Glut4 glucose transporter specifically in adipose tissue.¹ As other FAHFAs improve glucose tolerance, stimulate insulin secretion, and have anti-inflammatory effects, 12-POHSA may be a bioactive lipid with roles in metabolic syndrome and inflammation.¹