Introduction: Plasma levels of trimethylamine oxide (TMAO), a metabolite of TMA which is exclusively produced from choline, l-carnitine and betaine by the gut microbiota, has been shown to predict the risk of death from heart failure [1]. Plasma TMAO has also been reported to correlate with a range of non-communicable diseases such as cardiovascular disease (CVD), diabetes and neurodegenerative diseases which pose serious health, social and economic burdens worldwide [2, 3]. However, there are no current sustainable treatments to reduce TMAO levels in those at risk. Polyphenol-rich diets have been shown to protect against metabolic diseases such as CVD [4]. Aims and methodology: We investigated the potential and the capacity to which foods rich in polyphenols can alter TMA production from choline and betaine using the in-vitro batch fermentation human colon model [5], followed by metabolite analysis using LC-MS. We tested a black rice (BR) anthocyanin extract, an ellagitannin-rich pomegranate peel extract (DermogranateTM) and purified resveratrol. A  written informed consent was obtained from all participating subjects, the trial is registered at http:// www. Clinical trials. gov (NCT02653001) and the study was approved by the London—Westminster Research Ethics Committee (15/LO/2169) and the Quadram Institute Bioscience (Human Research Governance committee (IFR01/2015). Results: We demonstrate that BR anthocyanins (predominantly cyanidin-3-Glc) reduced TMA production from choline by 22% in a manner that is consistent with inhibition of the choline TMA-lyase pathway (F (1645, 1158) = 487.4, P< 0.05, N = 5). The Dermogranate®, which contains mainly ellagitannins including β-punicalagin, reduced TMA production from choline in a manner consistent with the inhibition of both the TMA lyase (F (914.7, 886.6) = 193.2, P < 0.0001, N = 4) and the betaine reductase pathway (F (173.5, 409.1) = 235.5, P < 0.001, N=4). We substantiated this notion by showing inhibition of betaine metabolism in the presence of choline and a lack of betaine production from choline in experiments in which no betaine was supplemented. DermogranateTM treatment also increased the production of lactic acid, suggesting a prebiotic activity (F (2.1, 15.36) = 13.26, P < 0.05, N=4). Resveratrol had no significant effect on TMA production from choline. Conclusion: We have demonstrated the potential for BR and DermogranateTM to be developed as functional foods that may be of benefit to people who have a high capacity to produce TMA/TMAO and are therefore at greater risk of developing chronic diseases or of extreme events after heart failure. The DermogranateTM may also have prebiotic activity.