Previous studies showed that HCA species not only improved glucose homeostasis by affecting glucagon-like peptide 1 (GLP-1) secretion through interaction with the intestinal receptors Takeda G protein-coupled receptor 5 and farnesoid X receptor in diabetic mice but were also strongly negatively correlated with diabetes and glycemic markers in several clinical cohorts (Zheng et al., 2021a). Here, GCG is linked to diabetes mellitus.