CD38 inhibition by flavonoids including apigenin and quercetin also improves glucose homeostasis and promotes fatty acid oxidation in the liver of mice with high-fat-diet-induced obesity, possibly through the activation of sirtuins such as Sirt1 and Sirt3 [96] (Figure 4a). This evidence concerns the gene SIRT1 and obesity due to melanocortin 4 receptor deficiency.