The short-ish story? When you eat red meat, certain bacteria in your gut metabolize L-carnitine in the meat. After a couple metabolic hops, that carnitine has turned into trimethylamine-N-oxide (TMAO) . . . and TMAO just loves forming arterial plaques in—you guessed it—your arteries.
Between mice and human trials, the study's authors (at the least) were pretty convinced that the carnitine/TMAO link could be a major player in red meat's connections to higher incidences of arteriosclerosis.
My favorite part was that they had a vegan eat steaks, for comparison. Because a vegan just might starve their meat-loving gut bacteria, to death. And as predicted, the vegan didn't spike in TMAO after eating meat like the frequent carnivores did . . . the bad meat-metabolism is entirely gut-bacteria driven.
(This could be bad news for meat-heavy Paleo dieters. Time will tell.)
Anyway, like I said, it's interesting. If further, broader investigations back up this link, it's possible that gut flora management (or less frequent, more intermittent meat-eating) could substantially reduce the ill effects of consuming carne.