INS and obesity due to melanocortin 4 receptor deficiency: Liquid chromatography mass spectrometry–based untargeted plasma metabolomics was applied in 60 participants with obesity with a large range of peripheral insulin sensitivity as determined via a two‐step HIEC with stable isotopes [6,6‐2H2]glucose and [1,1,2,3,3‐2H5]glycerol.