The investigators will conduct an open, controlled, randomized clinical trial, in patients with scheduled surgical intervention for CRC in the General Surgery and Digestive System Unit of the Virgen de la Arrixaca University Hospital (Murcia, Spain). All the included individuals must have passed the protocol of the Virgen de la Arrixaca University Hospital to be candidates for elective major surgery for CRC and must sign the informed consent after being informed of the objectives and the methodology of the study. The Helsinki Declaration will be followed during the duration of the project.

Patients will be randomized in a 1:1 ratio after receiving a diagnosis of CRC in the endoscopic evaluation; in the control arm, patients will receive standard nutritional recommendations, while patients in the intervention arm will be advised to follow a high-fiber diet rich in PUFAs (total dietary intake of at least 30 grams of fiber per day, and of at least 3 grams of PUFAs per day from food, not supplements) at least 4 weeks before surgery

Inclusion Criteria:

• Age between 18-80 years old.
• After clinical diagnosis of CRC (stage I-III), the doctor has recommended and arranged for CRC surgery

Exclusion Criteria:

• Clinical diagnosis of stage IV CRC.
• Current gastrointestinal illness other than gastroesophageal reflux disease or hemorrhoids (such as celiac disease, inflammatory bowel disease, malabsorptive bariatric procedures, etc.).
• Chronic liver or kidney disease.
• History of cardiac disease.
• Positive genetic test for inherited polyposis syndromes (such as familial adenomatous polyps, hereditary non-polyposis colon cancer syndromes, etc).
• Alcoholism or illicit drug use.
• Antibiotic use within the past 2 months.
• Dietary supplement use including pre- or probiotics within the past month.
• History of intestinal cancer, inflammatory bowel disease, celiac disease, or malabsorptive bariatric surgery.
• Inflammatory or connective tissue disease (such as lupus, scleroderma, rheumatoid arthritis, etc.).