Diet Quality and Fecal Bile Acid Composition

Background: Bile acids (BAs) are steroid metabolites generated by the liver from cholesterol. Their function is to support digestion of dietary fat, cholesterol, and fat-soluble vitamins. The gut microbiota metabolizes BAs that escape intestinal reabsorption to secondary BAs and other metabolites that are linked to increased risk of diseases including colorectal cancer (CRC). Diet plays a major role in BA metabolism and may be an important target for optimizing host-microbial BA metabolism for cancer prevention. Purpose: To examine fecal BA metabolites in relation to diet quality (Healthy Eating Index-2015, HEI-2015) among urban middle to older age adults. Methods: 135 participants were recruited from two academic medical centers. Stool, two 24-hour diet recalls, anthropometrics, and survey data were collected. Fecal BA profiling was completed using LC/MS. Diet quality was calculated using USDA's HEI-2015. Descriptive and inferential statistics were conducted. Results: Participants were 57% female, 51% African/American Black, mean age of 59.6 (±6.2) years and mean BMI of 31.4 (±6.9) kg/m2. Using USDA's cut-point for poor diet quality (HEI-2015 < 51 points), participants with poor diet quality were significantly more likely to be classified with obesity, self-report as African American/Black, report lower educational attainment, have increased secondary BAs, deoxycholic acid (DCA) and lithocholic acid (LCA), and lower 3-oxo-lithocholic acid and iso-allo-deoxycholic acid derivatives. In linear models, HEI-2015 (continuous) was a significant inverse predictor of DCA and LCA when controlling for BMI, race, and education. BMI was a significant positive predictor of DCA and LCA when controlling for HEI-2015, race, education. African American/Black was a significant inverse predictor of 3-oxo-lithocholic acid and iso-allo-deoxycholic acid when controlling for HEI-2015, BMI, and education. Conclusion. Poor diet quality and elevated BMI is associated with increased secondary BAs that have been linked to increased risk of CRC. Improving diet quality and reducing BMI may optimize host-microbial BA metabolism to prevent disease. African American/Black was an independent predicator of lower anti-inflammatory BA derivatives which warrants further investigation.