TMAO is derived from TMA and is oxidised to TMAO in our liver. So it is TMA that is the primary input. T<A is found naturally in both plant and animal sources and is prevalent in fish. It is made up from choline, lecithin, and L-Carnitine(apparently). The first two of these substances occur in plan-based sources, and are not prevalent in meat and not with red meat. Both of these first two are known to reduce inflammation and swelling, and the repair of cells in the body, They are not essential since our bodies can manufacture what is needed from other dietary components. A low level of choline leads to NAFLD apparently, and it is often added to feeding tube meals for those in the hospital to prevent fat build-up in the liver.
The third ingredient L-Carnitine is mainly derived from animal products especially red meat, and especially in organ meats (offal). It can be synthesized by the body from other amino acids, so is not essential. Its function is to act as a transferase enzyme to allow long-chain fatty acids to enter the mitochondria. Without Carnitine, these chains cannot be used by the body, and build up until broken up into smaller chains by rogue oxidants in the blood. Carnitine also acts to remove waste products from the mitochondria.
Carnitine is shown by meta-studies to reduce cardio mortality especially heart failure.
All three of the prime ingredients are used as supplements and are individually considered healthy. Combined they are accused of creating a monster (TMA) that acts primarily in our olfactory organs and allows us to smell and taste things. Apparently, an overdose of TMA can cause body odour akin to fish.
The gut microbes involved in synthesising TMA have not been identified, but a major antibacterial can kill the effect (and also the healthy biota too). Since bodybuilders use supplementation of all three primary ingredients it is not a recognised risk factor for that pastime and bodybuilders are not significantly succumbing to the effects of such supplementation. This observation does not disprove the animal meat is a killer theory, but it raises doubts.
