Obesity has a great impact on all body functions, as shown in Figure 3A. Recent research reveals that catechins possessing C-3 galloyl and B-5 hydroxyl group structures (e.g., EGCG, ECG) exhibit marked structure-function specificity in anti-obesity effects—they specifically promote the proliferation of the probiotic Akkermansia muciniphila, modulate the LPS/insulin resistance signaling pathway, and establish a bidirectional “catechin-microbiota” amplification loop, effectively ameliorating high-fat diet-induced obesity, fatty liver, and glucose-lipid metabolic disorders [55]. The gene discussed is INS; the disease is fatty liver disease.