Colorectal cancer in periooperative period patients (n=60) will be enrolled to this study. Participants will be divided into 4 groups as follows:

• group 1 (n=15) will receive 2 capsules (per day) of L. plantarum 299v L. plantarum 299v (Sanprobi IBS®) for 4 weeks
• group 2 (n=15) will receive L. plantarum 299v (2 capsules per day) and inulin (4 g) for 4 weeks
• group 3 (n=15) will receive placebo (2 capsules per day) and inulin (4 g) for 4 weeks
• group 4 (n=15) will receive placebo (2 capsules per day) for 4 weeks

Inclusion Criteria:

• age ≥18 oraz ≤65
• patients with colorectal cancer prior to surgical treatment
• qualification to surgery
• the treatment with chemotherapy and radiotherapy in preoperative period
• an appropriate swallowing
• patients agreement to take part in this study

Exclusion Criteria:

• the presence of other cancers than colorectal cancer
• inflammatory bowel diseases
• dysphagia
• intake of antibiotics, proton pump inhibitors, probiotics, and synbiotics 3 months befor taking part in this study