Many athletes and bodybuilders ingest carnitine supplements because of its reputation as a "fat burner."This notion does have some basis in fact, since carnitine is indeed required for the transport of fatty acids into the mitochondria portion of cells, where the fatty acids undergo oxidation ("burning") in a process called beta-oxidation. No one argues that point and it is an accepted biochemical truth. Since carnitine is involved in fat oxidation, at first it makes sense to consider carnitine supplements potential true fat-burners. But there are some details that make such a notion incorrect. But besides its role in fat oxidation, carnitine offers a number of other benefits that can prove useful even if the fat burning feature doesn't pan out. For example, carnitine has been shown in several human studies to dramatically improve the movement or motility of sperm. Many men are infertile because their sperm just doesn't move at an optimal rate. But supplying such men with three grams of carnitine can vastly improve sperm motility to the point that it cures infertility. When carnitine is provided to older people who are sedentary, it can help to relieve fatigue. Other studies show that it can effectively reduce muscle damage following exercise and thus increase training recovery. It can help those with diabetes by lowering insulin resistance and elevated glucose levels.
But when it comes to increased fat burning during exercise, carnitine doesn't seem to offer much benefit, except in limited cases. One reason for this is because while taking carnitine supplements can boost blood plasma levels to a significant degree, little or none gets into the muscle, the site of fat burning. Years ago, the late Charles Pollquin told me that he got great results in the athletes that he trained by providing them with intravenous carnitine. He also noted that the usual oral supplements did little or nothing to promote increased body fat loss.
The biggest critique about carnitine is that ingesting oral supplements raises levels of a substance called trimethylamine-N-oxide or TMAO. In a highly publicized study that appeared a few years ago, researchers noted a possible connection between ingesting carnitine and the advent of atherosclerosis. Since meat is one of the best food sources of carnitine, this led the researchers to suggest that it wasn't the fat or the cholesterol content of meat that causes a link to cardiovascular disease, but rather it was the carnitine content that was the problem. After oral ingestion, carnitine is converted into TMAO by enzymes in the liver and by intestinal bacteria. Some people who've ingested large doses of carnitine supplements have noted an odd, fishy smell. That comes from the increased production of TMAO by carnitine. But what the researchers who warned against eating meat or ingesting carnitine supplements failed to note was that fish contains 66-times more TMAO compared to meat. Indeed,when fish starts to go . . .