GCG and food allergy: Duodenal inflammation, mast cells, eosinophils, GNB3, interleukin (IL)-17F, IL-10, melatonin, gastric motility, impaired gastric accommodation, gastric slow waves, leptin, peptide YY, cholecystokinin, glucagon-like peptide 1, motilin, gastric emptying, tegaserod, itopride, prokinetics, acotiamide, gut microbiota, small intestinal bacterial overgrowth (SIBO), the interstitial cells of Cajal (ICCs), visceral hypersensitivity, functional magnetic resonance imaging (fMRI), bile acids, brain-gut axis, enteric nervous system, vagal nerve, food allergy, dopamine, acupuncture, electroacupuncture