INS and diabetes mellitus: However, it seems that long-term L-carnitine intake eventually converts to a metabolite called trimethylamine N-oxide (TMAO) (97–99), and increased circulating levels of this metabolite can increase the prevalence of diabetes (54% per 5 μmol/L increment of plasma TMAO) (100), nonetheless one study showed that increased TMAO plasma level by 30 μmol/L after 24 weeks of L-carnitine supplementation was not related to glucose, insulin and HOMA-IR levels changes (97).