The T-helper-1-cell transcription factor T-bet has a role in obesity-associated insulin resistance, Stolarczyk et al. reveal. In mice deficient in T-bet, insulin sensitivity is improved despite increased visceral adiposity compared with wild-type mice. Further experiments in mice showed that T-bet acts in the adaptive immune system, and that its absence from this system leads to the improved insulin sensitivity. The researchers speculate that obesity could be uncoupled from insulin resistance through the absence of T-bet and, therefore, that T-bet is a potential target for the treatment of insulin resistance and type 2 diabetes mellitus.