trans-Vaccenic acid is an ω-7 fatty acid that has been found in bovine milk fats.¹ Dietary administration of trans-vaccenic acid (1% w/w) reduces total body fat, mesenteric fat, and adipocyte size, increases inguinal fat mass, and decreases intestinal and hepatic triglyceride secretion in a rat model of obesity with features of metabolic syndrome.² It decreases hepatocellular ballooning and steatosis, markers of non-alcoholic fatty liver disease (NAFLD), in the same model. Dietary administration of a butter enriched with trans-vaccenic acid decreases serum cholesterol levels and the formation of aortic atherosclerotic lesions in Ldlr-/- mice.³