Highlights d CerS6, but not CerS5, deficiency protects from obesityassociated insulin resistance d CerS6, but not CerS5, regulates C 16:0 ceramides in mitochondria and MAMs d CerS6-derived C 16:0 sphingolipids interact with Mff d CerS6 and Mff regulate mitochondrial dynamics and insulin resistance in obesity

Highlights d CerS1 and derived C 18:0 ceramide are increased in skeletal muscle of obese mice d Conventional and muscle-specific CerS1 deficiency protects from insulin resistance d CerS1 deletion in muscle improves glucose metabolism via increased muscle-derived Fgf21 d CerS1 inhibition in muscle might provide an approach to treat insulin resistance