Intake of quercetin reduced body weight gain and attenuated serum insulin levels by reducing Firmicutes/Bacteroidetes ratio and inhibiting the growth of bacterial species Erysipelotrichaceae, Bacillus and Eubacterium cylindroides, which correlated with HFD-induced obesity (Etxeberria et al., 2015a). This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.