In particular, the metabolism of dietary substrates such as choline and l-carnitine to trimethylamine (TMA) and subsequently to trimethylamine oxide (TMAO) by a hepatic enzyme flavin-containing monooxygenase 3 (FMO3) is of interest due to the strong associations of high circulating TMAO concentrations with the risk of numerous metabolic diseases and the risk of death from heart failure [4–6]. Here, FMO3 is linked to metabolic disease.