Is There a Choline, Carnitine, Tryptophan Cancer Risk via Diet? Trimethylamine N-oxide (TMAO) and indole-3-acetic acid (IAA) are metabolites produced by gut microbiota from specific dietary precursors found in certain foods. TMAO production occurs from the metabolism of nutrients containing trimethylamine groups, such as choline, carnitine, and betaine. These precursors are abundant in: Red meat (e.g., … Continue reading A diet rich in choline, carnitine, and tryptophan may increase cancer risk by producing trimethylamine n-oxide (TMAO) and indole-3-acetic Acid (IAA) metabolites.