INS and obesity due to melanocortin 4 receptor deficiency: The present investigation demonstrates that, in youth with obesity, 1) MCRI is significantly lower in the presence of type 2 diabetes versus IGT and versus NGT, with no difference between the latter two; 2) MCRI is lower in Black versus White youth driven by the significant difference in MCRI in the presence of IGT and type 2 diabetes and not in NGT; and 3) MCRI is negatively correlated with fasting insulin and adiposity measures and positively correlated with PIS and β‐cell function.