TMAO

Production of TMAO by gut bacteria has been proposed as a mechanism linking foods such as beef and eggs with the development of atherosclerosis, and TMAO has gained attention as a candidate biomarker for cardiovascular disease [1].

That reading is contested. Landfald and colleagues point out that fish and seafood contain considerable amounts of TMAO and are generally accepted as good for the heart, a paradox they say has been neglected [1]. A 2026 narrative review of glycerophosphocholine (GPC, also called alpha-glycerophosphocholine [2]) describes TMAO as a metabolite associated with atherosclerosis progression but says its adverse effect remains debatable [3].

Choline and carnitine are among the nutrients gut bacteria turn into TMAO [1], so studies of these supplements can measure it. In a randomized crossover study of six healthy men, co-funded by the food manufacturer HiPP-Werk Georg Hipp OHG, researchers measured blood TMAO after single doses of four choline supplements, including alpha-GPC [2]. A study in healthy volunteers tracked TMAO in plasma and urine after acetyl-L-carnitine and carnitine supplements [4]. The alpha-GPC and acetyl-L-carnitine pages report what these studies found.

When a page mentions TMAO, read it as a change in a blood marker, not a measured health outcome. As noted above, whether a higher TMAO level carries any risk is still debated [3][1].

• Choline: one of the nutrients from which gut bacteria produce TMAO [1].
• Alpha-GPC: a choline-containing supplement studied in relation to TMAO production [3].