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New link discovered between CVD, red meat
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Carnitine, a compound abundant in red meat and used as a supplement in energy drinks, appears to promote atherosclerosis.
According to new research in Nature Medicine, bacteria in the human digestive tract metabolize carnitine, turning it into trimethylamine-N-oxide (TMAO), a metabolite previously linked to atherosclerosis. Researchers found that a diet high in carnitine promoted the growth of bacteria that metabolize carnitine, thus producing more TMAO.
Researchers studied carnitine and TMAO levels of omnivores, vegans and vegetarians, and examined clinical data on 2,595 patients undergoing elective cardiac evaluations. They also investigated the cardiac effects of a carnitine-enhanced diet in normal mice compared with mice with suppressed levels of gut microbes. TMAO altered cholesterol metabolism at multiple levels, according to a press release.
High carnitine levels in patients predicted increased risk for CVD and major cardiac events, including MI, stroke or death. However, this was observed only in patients with high TMAO levels.
In addition, the researchers found specific gut microbe types in patients associated with both plasma TMAO levels and dietary patterns. Vegans and vegetarians had significantly lower baseline TMAO levels compared with omnivores. Among vegans and vegetarians, consumption of a large amount of carnitine did not produce significant levels of the microbe product TMAO; however, omnivores that consumed the same amount of carnitine experienced production of significant levels, according to information in the release.
“Intestinal microbiota may thus contribute to the well-established link between high levels of meat consumption and CVD risk,” Robert A. Koeth, MD, of the department of cellular and molecular medicine at Cleveland Clinic, and colleagues wrote.
Previous research associated a diet high in red meat with increased CVD risk. However, the cholesterol and saturated fat content in red meat does not appear to fully explain the increased CV risks, according to the researchers.
These data suggest a new connection, the researchers said. “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 synthesize TMAO from carnitine, which may explain the cardiovascular health benefits of these diets,” Stanley Hazen, MD, PhD, vice chair of translational research for the Lerner Research Institute and section head of preventive cardiology and rehabilitation in the Miller Family Heart and Vascular Institute at Cleveland Clinic, stated in the release.
According to Hazen, “this process is different in everyone, depending on the gut microbe metabolism of the individual. Carnitine metabolism suggests a new way to help explain why a diet rich in red meat promotes atherosclerosis.”
The researchers said it is also important to study the safety of chronic consumption of carnitine supplements and the growth of bacteria that produce TMAO and potentially lead to atherosclerosis.
For more information:
Koeth RA. Nature Medicine. 2013;doi:10.1038/nm.3145.
Disclosure: The researchers report no relevant financial disclosures.