Research on TMAO


I have reported before on TMAO (trimethylamine N-oxide) that is produced by certain bacteria in your gut when you eat foods that contain lecithin, carnitine and choline, such as meat, eggs and dairy products. High levels of TMAO in the bloodstream have been associated with increased risk for heart attacks, strokes, clots, diabetes and certain cancers.

Among people seen in an emergency room for chest pain (European Heart Journal, Jan. 11, 2017), those with very high blood levels of TMAO were:
• six times more likely to die within the month
• twice as likely to die within seven years
• six times more likely to suffer a heart attack or stroke, or to require surgery to reopen a blocked artery
• far more likely to suffer a heart attack than those who just had high troponin, the traditional blood test doctors use in emergency rooms to determine if a patient is having a heart attack. These findings suggest that TMAO may be a more reliable test than troponin because troponin levels often do not rise until several hours a heart attack starts. A TMAO blood test costs only about $50, much less than the troponin test.

High Blood TMAO Predicts Disease
Earlier studies show that high levels of TMAO increase risk for:
• clotting by blood cells called platelets, the final step that causes heart attacks (Cell, March 24, 2016;165:1–14)
• markers of heart attacks and diabetes (Am J Clin Nutr, March 2016;103(3):703-711) and high cholesterol (N Engl J Med, April 25, 2013;368:1575-1584)
• colon cancer (Cancer Res, Dec 15, 2014;74(24):7442-52)
• prostate cancer (Am J Clin Nutr, Oct 2012;96(4):855-63)

High blood levels of TMAO also:
• predict which patients have blocked arteries anywhere in their bodies (J Am Heart Assoc, Oct 19, 2016;5(10). Patients with high levels of TMAO are far more likely to have blocked arteries leading to their brains and extremities as well as their hearts.
• predict which patients with chest pain are far more likely to die (J Am Heart Assoc, Jun 10, 2016;5(6). pii: e002816).
If these associations are confirmed by further studies, at least part of the prevention of heart attacks, strokes and some cancers is likely to be restricting animal products and possibly taking drugs to lower blood levels of TMAO.

How TMAO May Cause Arteriosclerosis
What you eat determines which types of bacteria live in your gut because your intestinal bacteria eat the same foods that you do. When you change your diet, you change your intestinal bacteria also (mBio, March 17, 2015;6(2):e02481-14). Red meat (meat from mammals), processed meats, dairy products and eggs contain lecithin, carnitine and choline. When you eat these animal products, you grow bacteria in your gut that convert the lecithin, carnitine and choline into TMAO (Curr Opin Lipidol, Feb 2014;25(1):48-53). However, if you seldom or never eat animal products, you are likely to have very low levels of bacteria in your gut that make TMAO. Feeding steak to vegans does not raise blood levels of TMAO (Nat Med, May 2013;19(5):576-85). Extensive research has shown that TMAO changes the liver's production of bile acids that punch holes in arteries to start plaques forming in the arteries of animals (Curr Opin Lipidol, Apr 2016;27(2):148-54).

My Recommendations
Research over the last 65 years has shown that eating red meat is associated with increased risk for heart attacks, strokes and some cancers, but there is still no agreement on why this association exists. The cholesterol and saturated fats in meat have been largely exonerated; see my report on The Saturated Fat Debate. While we await further research on TMAO and other possible explanations, I recommend limiting or avoiding red meat, processed meats and possibly limiting other animal products in your diet. 

Checked 1/11/19