Cleveland Clinic Scientists Study L-carnitine TMAO Heart Risks


American health scientists have discovered why red and processed meats raise risk of heart disease. While it has been known for a while that a diet high in saturated fat and salt can raise risk of developing heart disease, it was not understood why even eating lean red meats which are low in fat would also pose a health risk.

The new finding was discovered by scientists at the Cleveland Clinic in Ohio. Co-author Dr. Stanley Hazen, head of cardiovascular medicine at the Cleveland Clinic in Ohio, spoke with Nature Magazine to explain the findings.

It seems that the real problem is not the meat itself, but bacteria in the human gut which converts a nutrient found in beef into a compound which then causes an increase in plaques in the arteries. Red and processed meat is the catalyst but the real problem is another compound.


In the study l-carnitine was given to 77 people. Following the consumption of L-carnitine levels of the compound trimethylamine-N-oxide (TMAO) in the blood rose. This compound can alter metabolism and slow the removal of cholesterol from the walls of the arteries.


However, when L-carnitine was given to vegans and vegetarians, far less TMAO was produced than was seen in meat eaters. When the faeces were examined it was seen that meat eaters and vegetarians had very different bacteria make-up.

The conclusion was that meat eaters build up a colony of bacteria which can turn L-carnitine into TMAO, and this is what poses the greatest health risk.

Feeding Mice L-Carnitine Doubles Risk of Arterial Plaques

The researchers also found that giving mice L-Carnitine doubled their risk of developing arterial plaques – if they had their “normal” gu bacteria. When the mice were given antibiotics to cleanse their guts the presence of L-Carnitine did not increase the development of plaques.

New Approach To Diet and Health

Each person will have a slightly different bacteria colony inside their gut, which is dependent on a combination of genetics and lifestyle and total diet. For some people what is already inside their guts could be more important than what they eat.

It seems that being a vegetarian or vegan is healthier in terms of of gut flora. Meat should be eaten in moderation, especially meats which contain high levels of L-carnitine.

Dietary Sources of L-carnitine

As well as red meat (beef steak and ground beef), pork and bacon are also high in L-carnitine.


L-carnitine is also present in dairy products and in small quantities in asparagus, avocado, peanut butter, tempeh and wheat. Cod and chicken also contain L-carnitine.

Beef steak100 g95 mg
Ground beef100 g94 mg
Pork100 g27.7 mg
Bacon100 g23.3 mg
Tempeh100 g19.5 mg
Cod fish100 g 5.6 mg
Chicken breast100 g 3.9 mg
American cheese100 g 3.7 mg
Ice cream100 ml 3.7 mg
Whole milk100 ml 3.3 mg
Avocadoone medium2 mg
Cottage cheese100 g 1.1 mg
Whole-wheat bread100 g 0.36 mg
Asparagus100 g 0.195 mg
White bread100 g 0.147 mg
Macaroni100 g 0.126 mg
Peanut butter100 g 0.083 mg
Rice (cooked)100 g 0.0449 mg
Eggs100 g 0.0121 mg
Orange juice100 ml 0.0019 mg


Warning to Bodybuilders and Athletes

Many bodybuilders and athletes take L-Carnitine supplements along with additional dairy (whey) and meat. It is now thought that they are putting themselves at greater risk of cardiovascular disease.

People take L-Carnitine supplements to increase energy, promote weight loss and athletics performance. However, Dr. Stanley Hazen points out that there is not actually any science behind these claims, and he finishes by saying “I see no reason why anyone needs to take it.

Final Points

We also know that red meat and processed meat is linked with increased risk of colon cancer. The role of bacteria and L-carnitine could be involved here too.


Red meat + wrong bacteria = bad news for hearts by Chris Woolston,, 07 April 2013

Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis by Robert A Koeth,  Stanley L Hazen et alNature Medicine (2013) doi:10.1038/nm.3145. Published online 07 April 2013.




About Medimise

JP studied Health Sciences with the Open University between 2008 and 2011 and attained a Certificate in Health Sciences. Focus areas included T2 diabetes, trauma and repair, pain management, alcoholism, COPD, and cancer diagnosis and treatment. JP has been working as lead editor of several health publications since 2006 and works full time in the health industry.

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