Ceramides in focus Excess calorie intake can ultimately lead to a metabolic syndrome that interferes with fat or lipid metabolism. There are many different types of lipids, and it has been widely debated which are the true culprits underlying metabolic disorders. Chaurasia et al. report that ceramides are the major contributor to insulin resistance and fatty liver disease (see the Perspective by Kusminski and Scherer). This appears to be caused by the enzyme dihydroceramide desaturase 1 (DES1), which is normally involved in ceramide production by inserting a double bond into the backbone of the molecule. In mice fed a high-fat diet, deletion of DES1 improved glucose and lipid metabolism. Science , this issue p. 386 ; see also p. 319