INS and obesity due to melanocortin 4 receptor deficiency: Thus, to understand better the increased insulin-stimulated brain GU in severe obesity, we performed a series of brain 1H-MRS studies assessing concentrations of different metabolites often reported altered in obesity and insulin resistance: total N-acetyl-aspartate (NAA), myo-inositol, glutamine/glutamate (Glx), total creatine and total choline.