BILe Acid-gut Microbiome Axis MODification Through Diet Education for Colorectal Cancer Prevention

In this research study, the investigators are: * Investigating the effect of more plant-based and less animal-based food intake on bile acid metabolomic composition in stool among individuals with a history of colorectal adenoma. * Investigating the effect of more plant-based and less animal-based food intake on plasma bile acid metabolomic composition, the gut microbiome, circulating biomarkers and gene expression associated with colonic bile acid receptor activation and colorectal cancer among individuals with a history of colorectal adenoma. Based on the following evidence: * Growing evidence indicates that the gut microbiome and its metabolites play important roles in mediating the dietary effects on colorectal cancer risk * Secondary bile acids are increasingly appreciated as important metabolites underlying the metabolic link between Western diet, the gut microbiome, and colorectal cancer * Evidence suggests that secondary bile acids trigger a plethora of tumorigenic effects in the colon, including inflammation, oxidative DNA damage, and apoptosis resistance * Epidemiological studies have revealed that a higher circulating level of secondary bile acids, particularly deoxycholic acid and lithocholic acid, was associated with an increased risk of colorectal cancer * High fat intake has been repeatedly reported to increase secondary bile acids, but the findings on how other nutrients or foods in Western diet may influence secondary bile acids remain mixed The research procedures include screening for eligibility, study intervention, and scheduling two clinical research visits: * Initial visit - immediately before starting the dietary intervention * 1 week of observation prior to dietary intervention * 4 weeks of dietary intervention (increasing plant based food and reducing animal-based food) * Final visit (after completing the dietary intervention) At the Initial and Final visits, there will be a collection of lifestyle and nutritional questionnaire data, blood samples, and stool samples. The initial visit will establish the baseline data. The 1-week pre-intervention observation will establish baseline food diary data (every 2 days). The 4-week intervention phase will involve phone calls from study staff to guide participants in their diet changes, additional food diary entries (every 2 days), stool sample collection (every 7 days), and body weight reporting (every 7 days). It is expected that about 40 people will take part in this research study. This research is being supported by the National Cancer Institute.