UK expert rejects latest red meat and heart disease study
A UK medical expert has rejected the findings of a new study which claimed to find a link between a chemical found in red meat and heart disease.
The study, which was carried out by the Cleveland Clinic and published in the journal Nature Medicine, focused on carnitine – a compound found in meats such as beef, pork and lamb, which plays an essential role in transporting fatty acids to the part of the body’s cells that create energy.
Researchers said the study revealed that bacteria found in the human gut metabolises carnitine into trimethylamine-N-oxide (TMAO), which has been linked by previous research to atherosclerosis – the hardening or clogging of arteries. They added it also suggested a diet rich in carnitine promoted the growth of this bacteria, which resulted in even more TMAO being produced and compounded the risk.
Lead author Dr Stanley Hazen of the Cleveland Clinic said: "The bacteria living in our digestive tracts are dictated by our long-term dietary patterns.
"A diet high in carnitine actually shifts our gut microbe composition to those that like carnitine, making meat-eaters even more susceptible to forming TMAO and its artery-clogging effects. Meanwhile, vegans and vegetarians have a significantly reduced capacity to synthesise TMAO from carnitine, which may explain the cardiovascular health benefits of these diets."
However, Roger Leicester, a consultant surgeon and member of the Meat Advisory Panel, questioned the science behind the study and claimed that it does not conclusively show a link between red meat and heart disease.
The first part of the research was an examination of clinical data from 2,595 patients undergoing cardiac evaluations, which researchers said suggested that people with increased levels of carnitine faced a higher risk of heart disease and major cardiac arrest if they had "concurrently high TMAO levels".
Leicester pointed out that the study failed to take into account the "the plethora of well-established confounding lifestyle factors" that cumulatively contribute to increased risk of cardiovascular disease. "It therefore needs to be viewed in context and not in isolation," he said.
The second part of the research was a comparison of carnitine and TMAO in meat eaters, vegetarians and vegans. The researchers claimed that when the meat-eaters in the study consumed carnitine they produced "significant levels" of TMAO, but when the non-meat eaters consumed the same amount of the compound they did not.
However, Leicester pointed out that the study involved just five people, who were asked to consume an 8oz sirloin steak plus a 250mg supplement of L-carnitine. He added that there was no placebo-controlled trial for comparison and that the subjects were only given L-carnitine on three separate occasions. "This was not a study of significant time duration," he said.
He pointed out that while TMAO production increased in some subjects, "no hard clinical endpoints related to atherosclerosis were measured".
The final part of the research involved mice fed on a carnitine-rich diet. The researchers said that tests on the mice had revealed that TMAO altered the metabolism of cholesterol – thought to be responsible for the build-up of fatty deposits in arteries – which could explain why it promotes atherosclerosis.
However, Leicester pointed out that the mice in the study had been fed a carnitine in a food supplement, rather than with food containing the compound, which could give a different effect. "Mice are not a perfect model of human metabolism," he added.
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