Effect of a polyphenol-rich pomegranate extract on plasma trimethylamine N-oxide levels following an oral carnitine challenge: a randomized controlled crossover trial in healthy adults

Introduction Polyphenol-rich pomegranate extract has been shown to inhibit microbial trimethylamine (TMA) production from L -carnitine. Previous clinical studies have examined effects of polyphenol-rich interventions on fasting trimethylamine N-oxide (TMAO) concentrations but have not assessed pharmacokinetic TMAO responses following an oral carnitine challenge (OCC). We investigated whether a single dose of pomegranate extract attenuates the plasma TMAO response to an OCC in healthy adults. Methods This two-phase dietary intervention study enrolled 34 healthy, omnivorous adults. In Phase I, participants completed an OCC (1.5 g L -carnitine) to identify high TMAO producers (increase ≥ 5 μmol/L). Twenty high producers entered Phase II; an 18-day double-blind, randomized, placebo-controlled, crossover study with two 48-h pharmacokinetic interventions separated by a 10-day washout. Interventions consisted of an OCC with concurrent pomegranate extract (1.6 g) or placebo. Each OCC was preceded by a 48-h low-TMAO precursor run-in diet. Participants arrived fasted (>8 h), and all meals during the intervention periods were fully standardized to minimize dietary variability. Blood, urine, and stool samples were collected, and TMAO was quantified using LC-MS/MS. Differences in TMAO area under the curve (AUC) were analyzed using linear mixed-effects models. Results Ninety one percent of participants meeting the Phase I inclusion criteria produced substantial TMAO quantities from L -carnitine. This proportion exceeds that of earlier reports. Pomegranate extract did not reduce TMAO AUC in the full Phase II cohort (placebo/pomegranate ratio 0.993, 95% CI 0.81–1.22; P = 0.945; n = 16). However, a post hoc subgroup analysis showed that the effect of the pomegranate extract on plasma TMAO differed by age and sex. Conclusion Under tightly controlled dietary conditions, a single dose of pomegranate extract did not reduce post-OCC TMAO responses in the overall cohort. Post hoc analyses suggest potential sex- and age-dependent effects, warranting confirmation in larger, adequately powered studies. Clinical trial registration https://clinicaltrials.gov/ , identifier NCT06518343.