For decades, the primary explanation for why red meat raises cardiovascular risk focused on saturated fat and dietary cholesterol. Research published in Nature Medicine in 2013 by Dr Stanley Hazen at the Cleveland Clinic identified a second mechanism: trimethylamine N-oxide, or TMAO. When gut bacteria metabolise choline from eggs and red meat, and carnitine from red meat, they produce trimethylamine, which the liver converts to TMAO. Elevated blood TMAO promotes atherosclerosis independently of LDL cholesterol.
What the Research Shows
In a study of over 4,000 adults undergoing cardiac evaluation, TMAO levels predicted major cardiovascular events including heart attack, stroke, and death at 3 years, independently of conventional risk factors. Each standard deviation increase in TMAO was associated with a 23 percent higher risk of major cardiovascular events. A subsequent meta-analysis of 19 studies confirmed that higher TMAO was associated with significantly higher all-cause mortality and cardiovascular event risk.
Why Plant-Based Eaters Have Lower TMAO
Habitual plant-based eaters have gut microbiome compositions that do not efficiently produce trimethylamine from choline. When a vegan or long-term plant-based eater consumes a carnitine challenge, they produce far less TMAO than an omnivore consuming the same dose, because the bacteria that produce trimethylamine are not established in their gut. The gut microbiome effect is cumulative: years of plant-based eating progressively reduce TMAO-producing bacterial populations. This is one of the mechanisms by which dietary pattern, not just individual meals, determines cardiovascular risk.