Bile acids as colon carcinogens and coffee ingredients as antagonists

Circulating Bile Acids and Adenoma Recurrence in the Context of Adherence to a High-Fiber, High-Fruit and Vegetable, and Low-Fat Dietary Intervention

INTRODUCTION

Diet may affect bile acid (BA) metabolism and signaling. In turn, BA concentrations may be associated with cancer risk. We investigated (i) associations of BA concentrations with adenoma recurrence and (ii) the effect of a high-fiber, high-fruit and vegetable, and low-fat dietary intervention on serum BA concentrations.

METHODS

The Polyp Prevention Trial is a 4-year randomized, controlled trial that investigated the effect of a high-fiber, high-fruit and vegetable, and low-fat diet on colorectal adenoma recurrence. Among 170 participants who reported adhering to the intervention and 198 comparable control arm participants, we measured 15 BAs in baseline, year 2, and year 3 serum using targeted, quantitative liquid chromatography-tandem mass spectrometry. We estimated associations of BAs with adenoma recurrence using multivariable logistic regression and the effect of the dietary intervention on BA concentrations using repeated-measures linear mixed-effects models. In a subset (N = 65), we investigated associations of BAs with 16S rRNA gene sequenced rectal tissue microbiome characteristics.

RESULTS

Baseline total BA concentrations were positively associated with adenoma recurrence (odds ratio Q3 vs Q1 = 2.17; 95% confidence interval = 1.19-4.04; Ptrend = 0.03). Although we found no effect of the dietary intervention on BA concentrations, pretrial dietary fiber intake was inversely associated with total baseline BAs (Spearman = -0.15; PFDR = 0.02). BA concentrations were associated with potential colorectal neoplasm-related microbiome features (lower alpha diversity and higher Bacteroides abundance).

DISCUSSION

Baseline circulating BAs were positively associated with adenoma recurrence. Although the dietary intervention did not modify BA concentrations, long-term fiber intake may be associated with lower concentrations of BAs that are associated with higher risk of adenoma recurrence.

Bile Acids, Gut Microbes, and the Neighborhood Food Environment-a Potential Driver of Colorectal Cancer Health Disparities

Bile acids (BAs) facilitate nutrient digestion and absorption and act as signaling molecules in a number of metabolic and inflammatory pathways. Expansion of the BA pool and increased exposure to microbial BA metabolites has been associated with increased colorectal cancer (CRC) risk. It is well established that diet influences systemic BA concentrations and microbial BA metabolism. Therefore, consumption of nutrients that reduce colonic exposure to BAs and microbial BA metabolites may be an effective method for reducing CRC risk, particularly in populations disproportionately burdened by CRC. Individuals who identify as Black/African American (AA/B) have the highest CRC incidence and death in the United States and are more likely to live in a food environment with an inequitable access to BA mitigating nutrients. Thus, this review discusses the current evidence supporting diet as a contributor to CRC disparities through BA-mediated mechanisms and relationships between these mechanisms and barriers to maintaining a low-risk diet.

An investigation of cross-sectional associations of a priori-selected dietary components with circulating bile acids

BACKGROUND

A growing body of literature suggests chronically higher bile acid (BA) concentrations may be associated with multiple health conditions. Diet may affect BA metabolism and signaling; however, evidence from human populations is lacking.

OBJECTIVES

We systematically investigated cross-sectional associations of a priori-selected dietary components (fiber, alcohol, coffee, fat) with circulating BA concentrations.

METHODS

We used targeted, quantitative LC-MS/MS panels to measure 15 circulating BAs in a subset of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC; n = 2224) and Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO; n = 986) comprising Finnish male smokers and United States men and women, respectively. We used multivariable linear regression to estimate associations of each dietary component with log-transformed BAs; exponentiated coefficients estimate proportional differences. We included the median of the dietary component quartile in linear regression models to test for trend.

RESULTS

In ATBC, fiber was inversely associated with multiple circulating BAs. The proportional difference was -10.09% (95% CI: -19.29 to 0.16; P-trend = 0.04) when comparing total BAs among those in the highest relative to the lowest fiber quartile. Alcohol, trans fat, and polyunsaturated fat were positively associated with BAs in ATBC. The proportional difference comparing total BAs among those in the highest relative to the lowest alcohol quartile was 8.76% (95% CI: -3.10 to 22.06; P-trend = 0.03). Coffee and monounsaturated fat were inversely associated with BAs. The proportional difference comparing total BAs among those in the highest relative to the lowest coffee quartile was -24.03% (95% CI: -31.57 to -15.66; P-trend < 0.0001). In PLCO, no dietary components were associated with BAs except fiber, which was inversely associated with tauroursodeoxycholic acid.

CONCLUSIONS

Alcohol, coffee, certain fat subtypes, and fiber were associated with circulating concentrations of multiple BAs among Finnish male smokers. Given the potential role of BAs in disease risk, further investigation of the effects of diet on BAs in humans is warranted.