A chemical found in red meat helps explain why eating too much steak, mince and bacon is bad for the heart, say US scientists.
A study in the journal Nature Medicine showed that carnitine in red meat was broken down by bacteria in the gut.
This kicked off a chain of events which resulted in higher levels of cholesterol and an increased risk of heart disease.
Dieticians warned there may be a risk to people taking carnitine supplements.
There has been a wealth of studies suggesting that regularly eating red meat may be damaging to health.
In the UK, the government recommends eating no more than 70g of red or processed meat a day – the equivalent of two slices of bacon.
Saturated fat and the way processed meat is preserved are thought to contribute to heart problems. However, this was not thought to be the whole story.
“The cholesterol and saturated fat content of lean red meat is not that high, there’s something else contributing to increases in cardiovascular risk,” lead researcher Dr Stanley Hazen told the BBC.