Cancer remains a major global public-health challenge and a central focus of medical research. According to the International Agency for Research on Cancer (IARC, 2020), 19.29 million new malignant tumors and 9.96 million cancer deaths occurred worldwide, >90 % being solid cancers. Lung cancer alone accounted for 2.2 million new cases and 1.8 million deaths; >75 % of patients were already at an advanced stage at diagnosis. Current options for late-stage solid tumors are limited: surgery is often impossible because of metastasis; cytotoxic chemotherapy produces dose-limiting toxicities (grade Ⅲ-Ⅳ myelosuppression 15-40 %, mucositis 50-80 %); radiotherapy risks pneumonitis (5-15 %) or enteritis (5-20 %) when tumors abut vital organs; targeted agents succumb to acquired resistance after a median 9-13 months; and immune-checkpoint inhibitors achieve <40 % objective response with 7-15 % grade 3-4 immune-related adverse events.

Dietary intervention is therefore emerging as a promising adjunct. Dietary fibre protects against cardiovascular and metabolic diseases, yet intake is universally low. WHO and the Chinese Nutrition Society recommend 25-30 g total fibre per day (≈15-21 g insoluble), whereas Chinese adults consume only ~11 g insoluble fibre. High-fibre diets reshape gut microbiota, augment short-chain fatty acid (SCFA) production, strengthen intestinal barrier function, activate CD8⁺ T cells and dampen regulatory T cells, thereby enhancing anti-tumour immunity. A melanoma cohort showed improved progression-free survival under immunotherapy when fibre intake was high. Similar microbiota-immune axes may operate in colorectal and other solid cancers, but clinical data are scarce.

We therefore propose a study to examine whether a high-insoluble-fibre diet (>21 g/day) modulates gut-microbiota composition, metabolite profiles and peripheral-blood immune subsets in solid-tumour patients, and to evaluate consequent effects on treatment response and quality of life. The findings will clarify whether fibre-driven microbiota-immune crosstalk can be harnessed as a personalised nutritional strategy to improve cancer outcomes.

Inclusion Criteria:

• (1) Sign a written informed consent form before any study - related procedures are carried out.

  (2) Males or females, aged 18 - 80 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 child - bearing potential must agree to avoid sexual intercourse (heterosexual intercourse) or use a reliable and effective contraceptive method from the signing of the informed consent form until at least 6 months after the last administration of the study drug. In addition, the serum HCG (Human Chorionic Gonadotropin) test must be negative within 3 days before the start of the study treatment, and the subject must be non - lactating. A female patient is considered to be of child - bearing potential if she is post - menopausal but has not reached the post - menopausal state (non - menstrual period ≥ 12 consecutive months, and no other causes are found except menopause) and has not undergone sterilization surgery (such as hysterectomy, bilateral tubal ligation, or bilateral oophorectomy).

(11) If there is a risk of pregnancy, all subjects (regardless of male or female) need to use a contraceptive method with an annual failure rate of less than 1% throughout the treatment period until 120 days after the last administration of the study drug (or 180 days after the last administration of the chemotherapy drug)

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 the active ingredients or excipients of the study drug.

  (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.