FSTL1 and obesity due to melanocortin 4 receptor deficiency: In addition, we observed that FSTL1, FGF21, and IL6, which may be related to obesity and inflammation [83], were positively correlated with each other and with the class Actinomycetes, the family Rikenellaceae, the genus Alistipes, and the species A. okayasuensis. The class Actinomycetes ranges from harmless bacteria to pathogens that are extremely useful for antibiotic producers.