The purpose of this research study is to examine whether adding walnuts to your diet can have a beneficial effect on the gut bacteria population, inflammatory markers in the blood, and the tissue that lines the inside of the colon.

This is a 30-day dietary intervention study where participants will be asked to consume 2 ounces of walnuts daily for 21 days, and at the end of the study period they will come in for a routine colonoscopy. After being informed about the study and potential risks, participants giving written informed consent will first start a 7-day wash-out period where they will be asked to avoid foods high in ellagitannins for the duration of the study. In addition, participants will be asked to complete food and activity questionnaires, a walnut consumption log, and two sets of 3-day dietary records during their participation in the study. Participants will also be asked to provide three urine samples, two blood samples, and two stool samples at multiple time points, and 8-10 colon tissue specimens (biopsies) will be collected during their colonoscopy procedure for the purposes of this study.

Inclusion Criteria:

1. Men and women between the ages of 39-75 years old who meet the criteria of one of the following groups and are eligible to undergo a routine screening or surveillance colonoscopy for colorectal cancer (CRC):

   1. Individuals who have a family history of colon polyps or CRC in a first-degree relative diagnosed with CRC under the age of 65 years, or
   2. Individuals who are referred for colonoscopy following a positive fecal immunochemical test (FIT) or a positive Cologuard screening test and have not had a high-quality colonoscopy in the past 3 years, or
   3. Individuals who have a personal history of colon polyps

2. Willing and able to provide written informed consent for study participation

3. Willing to consume 2 ounces (56 grams) of walnuts daily for 3 weeks

4. Willing to avoid intake of EA/ET-rich foods and beverages (e.g., pomegranates, hazelnuts, pistachios, strawberries, raspberries, blackberries, oak-aged wines, and other items on a list given by researchers) and fermented dairy products containing viable Bifidobacteria or Lactobacilli)

5. Willing to stop taking dietary supplements, including probiotics

6. Willing to have two separate blood draws, as well as urine and stool collections

7. Willingness to comply with all study requirements

Exclusion Criteria:

1. Individual has a personal history of CRC, or a history of any malignancy (other than skin cancer) within the past 5 years
2. Individual meets the Amsterdam criteria for Lynch Syndrome or has a history of familial adenomatous polyposis (FAP)
3. 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
4. Use of antibiotics at least one month prior to the Screening Visit and for the duration of the study
5. Patients with severe medical illness or those at high risk for anesthesia, as determined by good clinical practice
6. Current evidence or previous history of ulcerative colitis or Crohn's disease
7. Colonoscopy performed for reasons other than screening or surveillance for CRC
8. HIV infection, chronic viral hepatitis
9. Allergy to walnuts or hypersensitivity to tree nuts
10. Peri-menopausal women with any chance or plan of pregnancy
11. Individuals with blood coagulation disorders or on anti-coagulant therapy
12. Any other condition that, in the opinion of the PI, might interfere with study objectives
13. No race/ethnicity, language or gender exclusions for this study