Red meat, which includes beef, lamb and pork, has a role to play in a balanced diet as it is a natural source of protein, iron, zinc and B vitamins. But red meat has long been associated with higher heart disease risk. Now, new research sheds light on the reason why.

According to a recent analysis, people who eat high quantities of red meat have higher blood levels of trimethylamine N-oxide, also known as TMAO.[i] TMAO is created when an individual ingests certain compounds found in abundance in red meat, particularly choline (which is also found in egg yolks and dairy products) and L-carnitine (also found in some energy drinks and supplements). In response, the bacteria in the gastrointestinal tract produce a compound called trimethylamine (TMA), which the liver then converts into TMAO.

The trouble with TMAO is that high levels may contribute to a heightened risk for clot-related events such as heart attack and stroke—independent of conventional risk factors and markers of inflammation.[ii]

The study monitored the impact of a four-week diet in which the primary protein source was derived from either red meat, white meat, or non-meat sources on plasma and urine concentrations of TMAO. After one month of the red meat diet, an increase in plasma TMAO levels was observed in the majority of subjects. On average, plasma TMAO levels increased approximately three-fold during the red meat diet, compared with the white meat or non-meat diets, with some subjects showing over a 10-fold increase. A similar significant increase in urine levels of TMAO were noted following chronic ingestion of the red meat containing diet.

The research also found that an individual’s TMAO levels dropped within a month of discontinuing to eat red meat and that people with largely vegetarian diets take longer to develop dangerous TMAO levels than regular red meat eaters.

Testing for TMAO

A pioneer in heart disease diagnostic innovations, Cleveland HeartLab has in research and innovations related to the influence of gut bacteria on heart health. In 2015, Cleveland HeartLab introduced the first TMAO lab-developed test to help clinicians identify TMAO blood levels in patients, empowering them with insights to help reduce disease risk.

In December 2017, Quest Diagnostics acquired Cleveland HeartLab. The laboratory in Cleveland, OH is now the site of Quest’s national Cardiometabolic Center of Excellence, which is dedicated to innovating the approach to cardiometabolic testing to help prevent disease and disese progression.


[i] Zeneng Wang, Nathalie Bergeron, Bruce S Levison, Xinmin S Li, Sally Chiu, Xun Jia, Robert A Koeth, Lin Li, Yuping Wu, W H Wilson Tang, Ronald M Krauss, Stanley L Hazen; Impact of chronic dietary red meat, white meat, or non-meat protein on trimethylamine N-oxide metabolism and renal excretion in healthy men and women, European Heart Journal.

[ii] Zhu W, Gregory JC, Org E, Buffa JA, Gupta N, Wang Z, Li L, Fu X, Wu Y, Mehrabian M, Sartor RB, McIntyre TM, Silverstein RL, Tang WHW, DiDonato JA, Brown JM, Lusis AJ, Hazen SL. Gut Microbial Metabolite TMAO Enhances Platelet Hyperreactivity and Thrombosis Risk. Cell. 2016 Mar 24;165(1):111-124. doi: 10.1016/j.cell.2016.02.011. Epub 2016 Mar 10.</span