An imbalance between the two species has been linked to obesity with conflicting results, but it seems that a reduced production of the microbiota-induced fermentation product butyrate (exerting anti-inflammatory and antioxidative properties and increasing insulin sensitivity in mice) and an increased release of LPS (already described as endotoxin) could favor obesity; the latter is characterized by a microbiota prone to harvest energy from diet [109, 110]. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.