RETN and obesity due to melanocortin 4 receptor deficiency: Further detailed studies (such as host metabolism by hormones [resistin, leptin, and adiponectin]; host immune response by biomarkers [TNF-α, IL-1, and IL-6]; metabolite profiles from the intestinal lumen; gene expression patterns of the anti-obesity microbes and host tissues; histology of intestine and liver; comparisons of herbivorous and carnivorous animals with omnivorous animals in the heme-SCP administrations) are required to understand the precise mechanisms underlying the prebiotic effect of hemoproteins.