Fiber to Reduce Colon Cancer in Alaska Native People

Randomization for the double blind, placebo controlled, clinical trial: Recruitment will
continue until 60 volunteers have completed the intervention study. Based on previous
experience with similar studies, we anticipate 20% of screened patients to be ineligible or
drop out, which means, so we plan on consenting and screening approximately 100 potential
participants. Baseline data from these participants will be retained. Individuals will be
randomized via minimisation (based on age, sex, polypectomy, high fish consumption, and BMI -
factors that might influence microbiota composition and function)) to either the resistant
starch (RS) group or the control digestible starch (DS) group upon completion of the
Stabilization Period.

1. RS Group: Participants will continue with their usual diet plus fiber supplement given
as a daily dose of 70g high-amylose maize starch (HAM-RS, HI-MAIZE®260: Ingredion
Incorporated, Bridgewater, NJ), which contains 42g of type 2 resistant starch, for 4
weeks. Data from previous studies[69] suggests that their usual diet will contain
approximately 13g dietary fiber/day, chiefly insoluble, indicating that total fiber
intake would be approx. 55g/d. Supplements will be pre-weighed out in batches from the
same source and kept in airtight containers. The supplement may be taken as a single or
divided dose dissolved in 250ml water, low fat milk, or orange juice

2. DS (Control) Group participants will continue on their usual diet, plus 70g of fully
digestible starch (waxy corn starch comprised of amylopectin, AMIOCA® corn starch,
Ingredion Incorporated, Bridgewater, NJ ) weighed out, analyzed, and prepared as
previously. The RS and control supplements will appear and taste similar, allowing for
coding and distribution in a double-blind fashion. The supplements will be equicaloric.

Interventions will include fecal and colonic content sampling for measurement of the
microbiome and metabolome, and flexible sigmoidoscopy to obtain mucosal biopsies before and
after the dietary supplementation.

Monitoring During the Clinical Trial: This will follow the scheme laid out on Figure 7. On
day 0, participants will visit the clinic and will be asked to save their first fecal sample
using our standard operating procedure developed and proven to be effective in our last
study. They will then be given their first supplement drink made up in their vehicle of
choice, and taken with a standard meal provided by the diet kitchen. During the trial, they
will be instructed on the use of a simple diary to be completed at home. This will record the
major food items consumed each day, the timing and completion of drink supplements, as well
as the bowel function questionnaire to assess daily GI tolerance, i.e. abdominal discomfort,
distension, gas, bowel frequency, nausea, vomiting. They will be asked to return to the
clinic for a follow-up appointment on day 7, 14 and 21 in order to repeat the fecal and
breath tests described above. At the same time, body weight will be monitored using one
scale. At the end of 4 weeks, participants will be asked to return to the clinic for repeat
of the colonic sampling performed at baseline.

Inclusion Criteria: Healthy AN volunteers (from GI standpoint) between 40-65 years (age at
which colon cancer screening colonoscopy is recommended in this population) and BMI between
18-35 Kg/m2. It should be noted that in our previous study, we found no difference in the
responses of the key parameters (mucosal biomarkers, butyrate and secondary bile acid
producers, fecal SCFA and bile acids) to increased fiber diets between those with normal
body weight, those overweight, and those who were obese (Nature Comm Supplement). Patients
who have, or have had noncancerous polyps removed previously by colonoscopy will be
eligible. Alaska Native race will be defined as those eligible to receive health care
through the Alaska Tribal Health System. Exclusion criteria: These are detailed under Human
Subjects. Participants will be ineligible if they have a history of familial adenomatous
polyposis or hereditary non-polyposis colorectal cancer, or have previous colonoscopic
evidence of inflammatory bowel disease or colon cancer. Also ineligible will be individuals
with known renal, hepatic, or bleeding disorders; previous GI surgery resulting in
disturbed gut function due to of loss of bowel or altered anatomy; or any form of chronic
GI disease resulting in disturbed gut function, diarrhea, and malabsorption. Individuals
with antibiotic use within the past 12 weeks, current steroids use, or on medical treatment
for diabetes, will also be excluded.