Clinical Characteristics, Lifestyle and Multi-omics Analysis in Autoimmune Gastritis

Inclusion Criteria: * Aged 35-75 years. * Type A atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathology showed no significant atrophy of antrum mucosa, but significant atrophy of the body or fundus mucosa, accompanied by positive blood and/or gastric fluid anti-parietal cell antibodies and/or anti-internal factor antibodies. No obvious tumor, deep ulcer, severe bile reflux, severe erosion, or active bleeding. Type B atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathological examination showed multifocal atrophy of gastric mucosa, mainly antrum involved. No obvious tumor, ulcer, moderate to severe bile reflux, moderate to severe erosion, multiple polyps (≥2) , or active bleeding. Chronic non-atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathology showed chronic inflammation of gastric mucosa with infiltration of lymphocytes and plasma cells, and no intrinsic glandular reduction. No obvious tumor, ulcer, moderate to severe bile reflux, moderate to severe erosion, multiple polyps (≥2) , or active bleeding. * Underwent colonoscopy within the past 5 years, and no obvious abnormalities such as inflammation, polyps, tumor, or ulcer were observed. * Have the cognitive level to understand the questionnaire and cooperate voluntarily. Exclusion Criteria: * Aged \<35 years or\>75 years. * Histopathology indicated dysplasia. * Long-term use of PPIs or H2-blockers for more than 3 months in the past 1 year. With a history of Helicobacter pylori eradication within the past 2 months. * Use of antibiotics, nonsteroidal anti-inflammatory drugs, probiotics, steroids, or immunosuppressants for more than 2 weeks within the past 2 months. * Severe constipation or diarrhea within the past 3 months, or notable changes in bowel habits within the past 3 months. * History of tumor, organ transplantation, or severe parasitic disease, other diseases of digestive system (such as inflammatory bowel disease, cirrhosis, pancreatitis, etc.), or serious infection. * History of severe trauma, major operation, extensive burn, cerebral vascular accident, severe organ failure (cardiac, hepatic, renal insufficiency, etc.), shock or sepsis within the past 6 months. * History of gastrointestinal surgery. * History of gastrointestinal bleeding, ileus, perforation. * Chronic metabolic, infectious, or endocrine diseases (such as hypertension, diabetes, hyperlipidemia, hyperuricemia, hyperpurine) that are not well controlled, whether or not treated with medications. * Vegetarians or had significant changes in eating habits within the past 3 months.