A study carried out by researchers from Cleveland Clinic in Ohio, US, has found that the chemical L-carnitine can increase the risk of suffering from heart problems. Saturated fat and the manufacturing process involved with how meat is preserved are widely believed to be related to heart problems, but many health experts think there is more to it. Lead researcher of the new study, Dr Stanley Hazen, commented: “The cholesterol and saturated fat content of lean red meat is not that high, there’s something else contributing to increases in cardiovascular risk.” L-carnitine is a nutrient which is contained in red meat, dairy products and some dietary supplements.  The study, published in the journal Nature Medicine, showed that the carnitine contained red meat was broken down by naturally occurring bacteria in the gut. However, this later resulted in higher levels of cholesterol and an increased risk of heart disease as the resulting broken down product - trimethylamine-N-oxide (TMAO), is known to speed up the build-up of plaque in arteries and cause them to harden (atherosclerosis) – a main cause of heart disease. Part of the researchers’ investigations was conducted in humans, whilst other testing was carried out with mice. Studies involving animals can be sometimes difficult to interpret, and some degree of caution should be shown when generalising the findings to humans. For the study, 77 healthy volunteers were administered a supplement of L-carnitine. Of this total, 26 were classified as vegans or vegetarians. Some of the meat-eaters in the group were told to eat an eight-ounce sirloin steak - this works out at around 180mg of L-carnitine. Researchers then gave antibiotics to the participants for a one week period. These prevented bacteria in their gut from converting L-carnitine into TMAO. After this, the 77 people again were given L-carnitine. Tests were conducted on blood and urine at the beginning of the study and up to three weeks following L-carnitine being given. Some of the people also had their faeces analysed. In addition, L-carnitine levels were checked in the blood of 2,595 other people, all of whom had attended a heart check-up. The researchers thought this would be an effective measure of assessing a potential link with L-carnitine levels and known cardiovascular disease, or risk of a cardiovascular event (i.e. a heart attack or stroke). Finally, plaque levels were studied in the arteries of mice and this was done by comparing mice fed normally against a group of mice fed L-carnitine, for a 10 week period. Some of these mice were given antibiotics beforehand. The main findings were: . Meat-eaters produced more TMAO compared to vegans or vegetarians following L-carnitine ingestion. . A ‘significant’ link was found between L-carnitine concentrations and risk of cardiovascular event in those having heart check-ups. However this was only for those with a high TMAO concentration. Researchers state they believe this shows that TMAO, rather than L-carnitine, is the main factor of this link. . A study of the faeces showed L-carnitine affected how much TMAO was in the blood. . Mice given L-carnitine, were at a double risk of developing a plaque build-up in their arterial walls, - but only when they had their normal gut bacteria. When the animals were given antibiotics to clear the gut, L-carnitine did not cause the same arterial wall build-up. Dr Hazen says that TMAO can be underestimated, and said: “It may be a waste product but it is significantly influencing cholesterol metabolism and the net effect leads to an accumulation of cholesterol. The findings support the idea that less red meat is better. I used to have red meat five days out of seven, now I have cut it way back to less than once every two weeks or so.”