CYP7A1 and obesity due to melanocortin 4 receptor deficiency: Research on HFD-induced obesity rats (also commonly used as a MASLD model) showed that HFD promoted BA intestine passive absorption to increase the concentrations of BAs, especially CDCAs, which activated the Fxr-Fgf15 pathway in the ileum to result in the mRNA expression of Cyp7a1 in liver down-regulation, which inhibited cholesterol metabolizing into primary BAs and contributed to the cholesterol level increase [47].