Red meat can harm the heart because of the way one of its nutrients is broken down by gut bacteria, research has shown.
By digesting the meat compound, L-carnitine, the bugs generate metabolites that promote hardening and narrowing of the arteries.
Scientists had previously identified one of the danger metabolites, trimethylamine-N-oxide (TMAO).
The latest research has uncovered a second, gamma-butyrobetaine, produced by the microbes at a rate 1000 times higher than TMAO formation.
Both contribute to atherosclerosis, the build up of hard fat and mineral deposits on the walls of arteries that can lead to heart attacks and strokes.