Effects of High-Fiber Diet on Gut Microbiota, Metabolism, and Immune Microenvironment in Solid Tumor Patients: A Clinical Study

Inclusion Criteria: * (1) Sign a written informed consent form before any study-related procedures are carried out. * (2) Males or females, aged 18-75 years old. * (3) Diagnosed with solid tumors by pathological tissue biopsy. * (4) According to the RECIST v1.1 (Response Evaluation Criteria in Solid Tumors Version 1.1) criteria, there is at least 1 measurable lesion (lesions previously treated with local therapies such as radiotherapy cannot be regarded as measurable lesions). * (5) ECOG (Eastern Cooperative Oncology Group Performance Status) score of 0-1. * (6) NRS-2002 (Nutritional Risk Screening 2002) score \< 3. * (7) BMI (Body Mass Index) ≥ 18.5 (can be adjusted appropriately according to the actual situation). * (8) Patients who can eat orally or through a feeding tube and can tolerate enteral nutrition. * (9) Sufficient organ function, and the subjects need to meet the following laboratory indicators: In the absence of granulocyte-colony-stimulating factor use in the past 14 days, the absolute neutrophil count ≥ 1.5×10⁹/L. Platelets ≥ 75×10⁹/L. In the absence of blood transfusion or erythropoietin use in the past 7 days, hemoglobin ≥ 8 g/dL. Serum albumin ≥ 3.0 g/dL. Total bilirubin ≤ 1.5× the upper limit of normal (ULN). Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) ≤ 2.5×ULN. In case of liver metastasis, ALT and/or AST ≤ 5×ULN, and total bilirubin ≤ 3×ULN. In case of liver or bone metastasis, Alkaline Phosphatase (AKP) ≤ 5×ULN. Creatinine clearance rate ≥ 50 mL/min (calculated according to the Cockcroft - Gault formula) or serum creatinine ≤ 1.5×ULN. International Normalized Ratio (INR) ≤ 1.5×ULN, Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) ≤ 1.5×ULN. Urine protein \< 2+ (if urine protein ≥ 2+, a 24-hour urine protein quantification can be performed, and subjects with a 24-hour urine protein quantification \< 2.0 g can be enrolled). * (10) Women of childbearing potential must agree to abstain from heterosexual intercourse or use a reliable and effective contraceptive method from the time of signing the informed consent form until at least 6 months after the last administration of concomitant anticancer treatment. A serum human chorionic gonadotropin (HCG) test must be negative within 3 days before initiation of the study intervention, and the participant must not be breastfeeding. Women are considered to be of childbearing potential unless they are postmenopausal, defined as amenorrhea for at least 12 consecutive months without an alternative medical cause, or have undergone surgical sterilization, such as hysterectomy, bilateral tubal ligation, or bilateral oophorectomy. * (11) If there is a risk of pregnancy, all subjects (regardless of sex) must use a contraceptive method with an annual failure rate of less than 1% throughout the treatment period and until 120 days after the last administration of concomitant anticancer treatment, or 180 days after the last administration of chemotherapy. Exclusion Criteria: * (1) Patients with cognitive impairment or mental illness who are unable to understand the study content. * (2) Patients with central nervous system or meningeal metastases. * (3) Patients with clinically symptomatic moderate or severe ascites (that is, those who require therapeutic paracentesis within 2 weeks before the start of study treatment; patients with only a small amount of ascites shown on imaging and no clinical symptoms can be enrolled). * (4) Patients with uncontrolled or moderate to severe pleural effusion and pericardial effusion. * (5) Patients with severe diarrhea, intractable vomiting, severe malabsorption syndrome, paralytic and mechanical intestinal obstruction; tracheoesophageal fistula, gastrointestinal perforation or gastrointestinal fistula, or abdominal abscess; patients with extra - gastrointestinal bleeding with a CTCAE (Common Terminology Criteria for Adverse Events) grade 3 or above within 6 months before the start of study treatment or grade 2 or above within 3 months (such as abnormal vaginal bleeding, hematemesis). * (6) Patients known to be allergic to any component of the dietary fiber supplement. * (7) Patients with poorly controlled diabetes. * (8) Patients with poorly controlled hypertension (systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg under routine antihypertensive treatment), with a history of hypertensive crisis or hypertensive encephalopathy. * (9) Patients with severe cardiovascular and cerebrovascular diseases, including cerebrovascular accident (CVA), transient ischemic attack (TIA), myocardial infarction, and major vascular diseases within 6 months before enrollment (including but not limited to aortic aneurysms requiring surgical repair or recent arterial thrombosis); patients with poorly controlled clinical symptoms or heart diseases, such as unstable angina pectoris, NYHA (New York Heart Association) heart failure grade II or above, left ventricular ejection fraction \< 50% on color Doppler echocardiography, or severe arrhythmias that cannot be controlled by drug treatment. * (10) Pregnant or lactating women. * (11) Other situations considered by the investigator as inappropriate for enrollment.