The levels of TRAP, CTSK, RANKL/OPG, matrix metalloproteinase-9 (MMP-9), TRAF6, urinary hydroxyproline, and urinary calcium were increased in the obesity-prone rats after consuming a high-fat diet, which was not seen in the obesity-resistant rats. This evidence concerns the gene CTSK and obesity due to melanocortin 4 receptor deficiency.