A red meat nutrient sold as a supplement for weight loss and muscle growth may damage the heart and arteries, new research suggests.
Capsules of L-carnitine are widely available in health food stores and online.
They are advertised as a fat-burning slimming aid and powerful muscle builder – and are also said to help people with heart conditions.
But new research in the US indicates a link between L-carnitine and heart disease. It may be a key reason why eating too much red meat can damage the heart, separate from the effects of saturated fat or cholesterol, say experts.
The studies show that L-carnitine is broken down by certain gut bacteria to produce a potentially harmful compound, trimethylamine N-oxide (TMAO).
Scientists found that high levels of L-carnitine in the blood were associated with heart disease, but only in individuals with raised TMAO.
Omnivorous individuals were found to produce more TMAO than vegetarians and vegans after consuming L-carnitine.
This suggests that, as well as containing L-carnitine, red meat favours the growth of gut bacteria that use the nutrient as an energy source, said the researchers.
A study of 2,595 patients undergoing heart check-ups showed “significant dose-dependent associations” between L-carnitine levels and the risk of coronary artery disease.
Links were also seen between L-carnitine and major events such as heart attacks, strokes and death.
In mice, L-carnitine supplements markedly increased TMAO levels and artery damage, but not if their gut bacteria was suppressed.