Consistent with previous literature, the investigators postulate that a leucine-restricted diet is safe and well-tolerated in gastric cancer patients receiving neoadjuvant chemo-immunotherapy. Furthermore, the investigators propose that this dietary regimen promotes the activation of immune cells within the tumor microenvironment (TME). When combined with neoadjuvant chemo-immunotherapy, it demonstrates synergistic anti-tumor efficacy, thereby improving patient prognosis.

In this study, participants were divided into an intervention group and a control group. Both groups received four cycles of neoadjuvant therapy comprising Oxaliplatin, S-1, and the PD-1 inhibitor Sintilimab. The intervention group implemented a 3-day leucine-restricted diet during each cycle, gradually resuming a normal diet thereafter, whereas the control group maintained a standard normal diet throughout the treatment period. This design was established to evaluate the safety and efficacy of the leucine-restricted diet in the context of neoadjuvant chemo-immunotherapy for gastric cancer.

Inclusion Criteria:

• Pathological Confirmation: Histologically confirmed locally advanced gastric cancer.
• Demographics: Aged 18 to 70 years, inclusive, regardless of gender.
• Dietary Capability: Capable of oral intake or receiving a liquid diet via nasogastric tube.
• Consent: Willing to participate in the study and have signed the Written Informed Consent Form (ICF).
• Staging and Treatment Indication: No evidence of distant metastasis on imaging examinations (such as CT or PET-CT), with a clinical stage of locally advanced gastric cancer, indicating the need for neoadjuvant chemo-immunotherapy prior to surgery.
• Exclusion of Other Malignancies: No concurrent primary malignant tumors other than gastric cancer.

Exclusion Criteria:

• Cognitive or Psychiatric Impairment: Cognitive dysfunction or psychiatric disorders severe enough to prevent the patient from understanding the study content or providing informed consent.
• Diabetes Mellitus: Diagnosis of Type 1 or Type 2 diabetes mellitus.
• Gastrointestinal Conditions: Presence of severe diarrhea, intractable vomiting, severe malabsorption syndrome, paralytic or mechanical intestinal obstruction, or active gastrointestinal bleeding.
• Allergy/Hypersensitivity: Known hypersensitivity or allergy to any of the main components of the leucine-deficient nutritional powder.
• Concomitant Supplements: Current use of other nutritional supplements that may potentially confound the study results or affect the evaluation of efficacy.
• Treatment Tolerance: Inability to tolerate neoadjuvant chemo-immunotherapy, or occurrence of severe gastrointestinal adverse events following such treatment.
• Pathological Diagnosis: Postoperative pathological diagnosis confirming non-primary gastric cancer (e.g., metastatic tumors from other origins).