A single arm, prospective, single center Phase1/2 Dietary intervention trial for subjects diagnosed with colorectal cancer and scheduled for tumor resection more than 21 days from informed consent. Subjects will be provided 21 days of standardized High-fiber/low-fat meals and complete a food diary up until lunch on the day prior to surgery. Blood samples will be collected at baseline and on the day of surgery. Stool samples will be collected throughout the dietary intervention period at specific timepoints, on the day of surgery, and 30 days post-surgery. Tissue from the tumor resection will be isolated for organoid cultures. Subjects will be followed per standard of care for up to 5 years or disease recurrence, whichever comes first. Subject may be treated for their cancer prior to surgery and/or during the follow-up period.

Inclusion Criteria:

• Must have histologically or cytologically confirmed colorectal adenocarcinoma.
• Planned for primary tumor resection at the University of Chicago Medicine ≥21 from date of obtained informed consent. Patients with metastatic disease but undergoing primary site resection are eligible for the study.
• Age ≥18 years.
• Patients <18 years of age, children are excluded from this study, because they have unique nutritional requirements that might not be met by with the standardized diet. The food in the diet is designed for adults and would not be feasible for children, especially those attending school. In addition, colon cancer is extremely rare in children.
• May have received neoadjuvant therapy (chemotherapy, radiation).
• Patients with Hepatic arterial infusion (HAI) pumps are considered eligible.
• Ability to understand and willing to sign an informed consent, participate in the dietary intervention, collect stools, donate blood, and complete a pre-nutritional evaluation and compliance/patient satisfaction survey.

Exclusion Criteria:

• Previous ostomy (ileostomy or colostomy) or definitive plan for an ostomy (ileostomy or colostomy) during the procedure.
• Antibiotic exposure within 60 days before diet initiation. Antibiotic exposure is defined as a 'course of treatment to treat an infection'. Prophylactic antibiotics prior to a procedure is okay.
• Prebiotic/Probiotic exposure within 60 days before diet initiation.
• Concomitant separate malignancy.
• Allergy to perioperative medications (oral neomycin/metronidazole for bowel preparation, intraoperative prophylactic intravenous cefazolin and metronidazole).
• Patients who are pregnant are not eligible for the study. Pregnant women are excluded from this study because the preoperative diet is not specifically formulated to meet the specific nutritional requirements during the prenatal period.
• History of inflammatory bowel disease
• Severe food allergies precluding the ability to tolerate the standardized dietary intervention.
• Patients with uncontrolled intercurrent illness