Diet-related gastrointestinal reactions are mainly due to food stimulation of intestinal mechanoreceptors, chemoreceptors (e.g., capsaicin), or alteration of gastrointestinal transport function, osmotic pressure, or secretion. The specific mechanisms are as follows: 1. Food allergy —- According to statistics, food allergy exists in 1% to 4% of the American population. The mechanisms of food allergy can be divided into IgE-mediated (type 1 hypersensitivity) and non-IgE-mediated. IgE-mediated allergic reactions have an acute onset and occur most often with foods such as peanuts, nuts, eggs, milk, soy, fish, shells, strawberries, and wheat. The most common allergic reaction is acute urticaria, and common gastrointestinal reactions include nausea, dysphagia, abdominal pain, vomiting, and diarrhea. Skin prick tests are more valuable than radioallergen adsorption tests for the diagnosis of IgE hypersensitivity reactions. Non-IgE-mediated hypersensitivity reactions are mediated by Th2 cells and have a slow onset, with symptoms confined to the gastrointestinal tract. Hong Zifu, Department of Anorectology, Guang’anmen Hospital, Chinese Academy of Traditional Chinese Medicine 2. Food intolerance —- Food intolerance reflects a non-immune response to a variety of disease processes, including non-celiac gluten sensitivity (NCGS), the effects of chemical components in food (e.g. histamine, glutamates, caffeine), enzyme deficiencies (e.g., lactase), transport disorders (e.g., fructose), and effects of short-chain carbohydrates in foods. In particular, food intolerance is present in 50% to 70% of patients with IBS and severely affects the quality of life of patients. Food-induced gastrointestinal symptoms are highly prevalent in women. Common intolerant foods include: high-carbohydrate diets, coffee, alcohol, milk, chocolate, beans, onions, cabbage and foods high in fat and spices. 3. Lactase deficiency —- is the enzyme most closely associated with food intolerance Deficiency. Fructose is a monosaccharide that often causes abdominal discomfort in patients with IBS. Fructose absorption in the small intestine is low due to the limited amount of fructose transporter GLUT-5 in the epithelial cells of the small intestine. Unabsorbed fructose accelerates intestinal motility and increases intestinal gas production. 50% of healthy volunteers exhibit fructose malabsorption after 25 g of oral fructose, and up to 75% after 50 g of oral fructose. Short-chain carbohydrates, usually found in grains, fruits, vegetables, legumes, and nuts, include fructans, oligogalactans (galactosomes), and polyols. These substances are difficult to absorb in the small intestine and can increase the osmotic pressure in the large intestine and ferment colon bacteria, leading to gastrointestinal discomfort. Colonic bacterial fermentation in turn produces hydrogen, methane, carbon dioxide and short-chain fatty acids.4. Altered intestinal osmolality —- is a potential pathogenic mechanism for diet-related symptoms of IBS, which are more common in patients with diarrheal IBS (IBS-D). Some studies have found that microscopic intestinal mucosal epithelial damage, intraepithelial lymphocytosis, and widening of the villi gap are more frequent in patients who consume wheat, soy, milk, and yeast.5. Visceral hypersensitivity —- Compared to healthy populations, patients with intestinal disease The clinical symptoms of SIBO are not specific and are associated with food intolerance, intestinal micro-ecological disorders, and gastrointestinal symptoms. The clinical symptoms of SIBO are not specific and are similar to those of food intolerance and intestinal microecological dysbiosis. There is no practicable gold standard for testing. 6. Intestinal microecology —- alterations in the intestinal microbiological environment brought about by dietary indiscretion and lack of moderation can lead to clinical symptoms with different manifestations such as diarrhea, bloating, and constipation.