By Joseph E. Scherger, MD, MPH

Core Faculty, Eisenhower Health Family Medicine, Residency Program, Eisenhower Health Center, La Quinta, CA; Clinical Professor, Keck School of Medicine, University of Southern California, Los Angeles

Dr. Scherger reports no financial relationships relevant to this field of study.

SYNOPSIS: The gut microbial metabolite trimethylamine N-oxide (TMAO) is a predictor of coronary artery disease (CAD). TMAO forms mainly through eating red meat and other animal products, such as eggs and dairy. Long-term changes in TMAO is a predictor of CAD and speaks to the benefits of a plant-based diet to prevent heart disease.

SOURCE: Heianza Y, Ma W, DiDonato JA, et al. Long-term changes in gut microbial metabolite trimethylamine N-oxide and coronary heart risk. J Am Coll Cardiol 2020;75:763-772.

Heianza et al conducted the first longitudinal, prospective study of heart risk from elevated trimethylamine N-oxide (TMAO) levels. The authors used the Nurses’ Health Study to obtain baseline TMAO levels, and followed 760 healthy women from 1989-1990 to 2000-2002. The increase in coronary heart disease (CAD) had a linear relationship with TMAO levels. For every one standard deviation increase in TMAO levels, there was a 33% increase in CAD risk. Women with the largest increases in TMAO levels had a 67% higher risk for CAD. TMAO is formed when gut bacteria metabolize nutrients such as choline, L-carnitine, and phosphatidylcholine found in red meat, egg yolk, and high-fat dairy products. This produces trimethylamine, which is converted into TMAO in the liver. TMAO affects lipid metabolites in the liver in such a way as to facilitate dyslipidemia. In high amounts, TMAO increases the risk for myocardial infarction, stroke, and all-cause death.


Advocates of a whole food, plant-based diet use research data surrounding TMAO to argue against the consumption of animal food products, especially red meat, but also eggs and dairy. The data are compelling enough to argue for limiting such exposure. The two healthiest diets by research data are a version of the Mediterranean diet and a whole food, plant-based diet. The Mediterranean diet emphasizes plants, and the meat content is only about 10% of the whole.1 Most seafood is not a source of TMAO. This would speak to a pescatarian diet.2 Primary care physicians should be aware of TMAO and its cardiac disease risks. This is part of recommending healthy diets. TMAO can be measured in the blood, and most commercial labs offer the test. I do not conduct this testing due to dietary fluctuations, but I do use information about TMAO to recommend healthy dietary choices that include limiting the consumption of animal products.


  1. Mayo Clinic Staff. Mediterranean diet: A heart-healthy eating plan. June 21, 2019.
  2. WebMD. What is a pescatarian?