Inclusion Criteria:  Individuals in one of the following groups:  Men and women between the ages of 40 to 75 years old, who are scheduled to undergo a routine screening or surveillance colonoscopy for colorectal cancer (CRC) and have a family history of CRC in a first degree relative diagnosed with CRC under the age of 60 years, or Men and women between the ages of 45 to 75 years old, who are referred for colonoscopy following a positive fecal immunochemical test (FIT) and have not had a high quality colonoscopy in the past 3 years Willing and able to provide written informed consent for study participation Willing to consume 2 ounces of walnuts daily for 3 weeks Willing to avoid intake of ellagic acid/ellagitannin-rich foods (e.g., pomegranates, hazelnuts, pistachios, strawberries, raspberries, blackberries, oak-aged wines, and other food on a list given by researchers) and fermented dairy products containing viable Bifidobacteria or Lactobacilli) Willing to stop taking dietary supplements, including probiotics Willing to have 2 separate blood draws, as well as urine and stool collections Willingness to comply with all study requirements  Exclusion Criteria:  Individual has a personal history of CRC, or a history of any malignancy (other than skin cancer) within the past 5 years Individual meets the Amsterdam criteria for Lynch Syndrome or has a history of familial adenomatous polyposis (FAP) Individual has been treated with immunosuppressive agents or systemic steroids, excluding inhalers, at least two weeks prior to the Screening Visit and for the duration of the study Use of antibiotics at least one month prior to the Screening Visit and for the duration of the study Patients with severe medical illness or those at high risk for anesthesia, as determined by good clinical practice Current evidence or previous history of ulcerative colitis or Crohn's disease Colonoscopy performed for reasons other than screening or surveillance for CRC HIV infection, chronic viral hepatitis Allergy to walnuts or hypersensitivity to tree nuts Peri-menopausal women with any chance or plan of pregnancy Individuals with blood coagulation disorders or on anti-coagulant therapy Any other condition that, in the opinion of the PI, might interfere with study objectives No race/ethnicity, language or gender exclusions for this study