To investigate whether the positive rates of methane and hydrogen breath test were different between the experimental group and the control group.

Small intestinal bacterial overgrowth (SIBO) refers to a syndrome of gastrointestinal symptoms caused by changes in the number and/or type of bacteria in the small intestine, and is considered to be secondary to changes in intestinal anatomy, slowing of intestinal motility, or abnormalities in gastrointestinal function. Clinical symptoms of SIBO are atypical, and are mainly characterized by bloating, belching, abdominal pain, diarrhea, constipation, and changes in stool shape, color, odor, and other characteristics. Since the clinical symptoms of SIBO are not specific and the clinical diagnosis criteria are not standardized, its treatment has not been given enough attention.

Inclusion Criteria:

Inclusion criteria for the experimental group:

1. Age 18-65 years old and gender;
2. Patients with functional gastrointestinal disease are characterized by abdominal symptoms (abdominal distension, early satiety, diarrhea, constipation, abdominal pain, etc.)
3. have the autonomy to complete methane and hydrogen breath testing and gastrointestinal symptom scoring independently or with medical assistance;
4. able to complete the signing of informed consent as required.

Inclusion criteria for the control group:

1. Age 18-65 years old and gender;
2. Healthy individuals without obvious typical gastrointestinal symptoms;
3. Autonomy to complete methane and hydrogen breath testing and gastrointestinal symptom scoring independently or with medical assistance;
4. Ability to complete the informed consent form as required.

Exclusion Criteria:

1. Patients whose gastroenteroscopy within one year indicated malignant tumor of digestive tract, or whose above examination proved peptic ulcer within two months;
2. A history of malignant tumors of the digestive system (not limited to the digestive tract), a history of inflammatory bowel disease, or a history of false or mechanical ileus;
3. Gastrointestinal resection, appendectomy and cholecystectomy within one year;
4. History of gastrointestinal perforation, gastrointestinal bleeding, cholangitis, acute and chronic pancreatitis within one year;
5. There is evidence of gastrointestinal tract infection (Helicobacter pylori, acute infectious enteritis);
6. History of type I diabetes and primary hypothyroidism;
7. Confirmed lactose malabsorption, lactose intolerance, and pancreatic exocrine insufficiency;
8. Within 4 weeks, a history of antibiotic administration;
9. Within 2 weeks, history of endoscopy;
10. Within 1 week, history of taking gastrointestinal stimulants, probiotics, laxatives;
11. 1 day prior to testing, eating fermentable foods (yogurt, kimchi, soy sauce, tempeh, oats, beer, etc.);
12. Not fasting 8 hours prior to testing;
13. Smoking, strenuous exercise 2 hours before and during the test;
14. Preparation for pregnancy, pregnancy, breastfeeding women, or overall poor compliance, or other conditions that the investigator believes need to be excluded.

Subjects attending the digestive (internal) Department and physical examination department/physical examination center of each center.