Bad News for Red Meat Lovers

Atherosclerosis risk rises from ingesting a compound found in red meat

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) While it’s been shown that fat and cholesterol in a juicy hamburger may be unhealthy for your heart, a compound called carnitine may be even worse for you.

A new study has found that an increased carnitine level in a patient may be a strong predictor of cardiac events like heart attack, stroke and death.

This research also highlighted the potential benefits of vegetarian and vegan diets.

"Limit eating red meat."

Beef, lamb, pork and duck are rich in carnitine—a compound that’s also used as a supplement in energy drinks, energy pills and some weight loss treatments.

Stanley Hazen, MD, vice chair of Translational Research for the Lerner Research Institute and section head of Preventive Cardiology & Rehabilitation in the Miller Family Heart and Vascular Institute at the Cleveland Clinic, and Robert Koeth, a medical student at the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University in Ohio, led the study.

Investigators examined clinical data on 2,595 omnivores, vegans and vegetarians, noting levels of carnitine and trimethylamine-N-oxide (TMAO) in each of these groups.

The authors observed that baseline TMAO levels were significantly lower among vegans and vegetarians than omnivores.

Bacteria living in the human digestive tract metabolize carnitine and turn it into TMAO, a metabolite linked to the promotion of atherosclerosis in humans, according to a 2011 study.

Making the problem of carnitine consumption even worse, scientists found that eating a diet high in carnitine promotes the growth of the bacteria that changes the compound into the TMAO.

To further support the study, Dr. Hazen and his team fed sirloin steaks to five omnivores and one vegetarian. Shortly after the steaks were eaten, they measured a spike in TMAO in the five meat eaters but not in the one vegetarian.

“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,” said Dr. Hazen.

“Meanwhile, vegans and vegetarians have a significantly reduced capacity to synthesize TMAO from carnitine, which may explain the cardiovascular health benefits of these diets. Carnitine metabolism suggests a new way to help explain why a diet rich in red meat promotes atherosclerosis.”

When it comes to carnitine use in energy drinks and other products, Dr. Hazen stresses that more research needs to be done.

"Carnitine is not an essential nutrient; our body naturally produces all we need," he said. "We need to examine the safety of chronically consuming carnitine supplements as we've shown that, under some conditions, it can foster the growth of bacteria that produce TMAO and potentially clog arteries."

Dr. Hazen and his team also examined the cardiac effects of a carnitine-enhanced diet in normal mice compared to mice with suppressed levels of gut microbes, and discovered that TMAO alters cholesterol metabolism at multiple levels, explaining how it enhances atherosclerosis.

In a 2011 Nature study, these researchers first discovered that people are not predisposed to cardiovascular disease solely because of their genetic make-up, but also based on how the microorganisms in their digestive tracts metabolize lecithin, a compound with a structure similar to carnitine.

Deborah Gordon, MD, an integrative physician at Madrona Homeopathy in Ashland, Oregon, who was not involved in this study, told dailyRX News that the results of this research should be taken in balance with other information and research.

"There are many sources of dietary TMAO, and notably higher levels than red meat are in saltwater fish, mollusks and crustaceans," said Dr. Gordon. "Recent epidemiological studies strained to find a very slight association between meat-eating and mortality, including heart disease."

Dr. Hazen has said that the study does not mean that red meat is entirely bad or should be avoided completely. Red meat has its benefits—it contains protein and B vitamins.

The most interesting point of the study may be the pivotal role of gut bacteria plays in an individual's health, according to Dr. Gordon. "If Dr. Hazen's meat eaters shunned fruits and vegetables on a regular basis, their flora [microorganisms that live in the digestive
tract] were likely lopsided, with the meat-loving bacteria predominating."

Overall, Dr. Gordon endorses eating grass-fed beef and eating meat as part of a well-balanced diet.

This study was published April 7 in Nature. Dr. Hazen has been paid as a consultant or speaker by the following companies: Cleveland Heart Lab., Esperion, Liposciences, Merck & Co. and Pfizer. He has received research funds from Abbott, Cleveland Heart Lab, Esperion and Liposciences and has the right to receive royalty payments for inventions or discoveries related to cardiovascular diagnostics from Abbott Laboratories, Cleveland Heart Lab, Frantz Biomarkers, Liposciences and Siemens.

Reviewed by: 
Review Date: 
April 8, 2013
Last Updated:
August 14, 2013