The invention includes methods and compositions for treating a metabolic disorder, such as metabolic syndrome, hyperlipidemia and associated disorders, such as obesity and diabetes. The invention includes a method of treating a human subject comprising administering 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) to the subject. Further provided is the use of 12,13-diHOME as a biomarker for identifying brown adipose tissue (BAT) activation in human subjects.