IRS1 and Insulin resistance: Protocatechuic acid (PCA), a phenolic metabolite of C3G found in numerous plant species, especially in the endemic Chinese herb Eucommia ulmoides native to Zhangjiajie, Hunan Province, has been shown to improve inflammation and insulin resistance in mice by upregulating fibroblast growth factor 1 (Fgf1), insulin-like growth factor binding protein 2 (Igfbp2), insulin receptor substrate 1 (Irs1), and insulin receptor substrate 2 (Irs2) [26] and to modulate gut microbiota in piglets (Pig Improvement Company line 337 × C48, 28 d of age, 8.87 kg ± 0.11 kg BW) [27].