Source: National Institutes of Health (NIH)
Trimethylamine N-oxide (TMAO) is a dietary byproduct that is formed by gut bacteria during digestion. The chemical is derived in part from nutrients that are abundant in red meat. High saturated fat levels in red meat have long been known to contribute to heart disease, the leading cause of death in the United States. A growing number of studies have identified TMAO as another culprit.
The exact mechanisms by which TMAO may affect heart disease is complex. Prior research has shown that TMAO enhances cholesterol deposits in the artery wall. Studies also suggest that the chemical interacts with platelets—blood cells that are responsible for normal clotting responses—to increase the risk for clot-related events such as heart attack and stroke.
To investigate the effects of dietary protein on TMAO production, a research team led by Dr. Stanley L. Hazen at the Cleveland Clinic enrolled 113 healthy men and women in a clinical trial. The participants were given three diets for a month in random order. All meals were prepared for them, with 25% of calories from protein. The dietary proteins came from either red meat, white meat, or non-meat sources. The research was largely supported by NIH’s National Heart, Lung, and Blood Institute (NHLBI). Results were published on December 10, 2018, in European Heart Journal.
When on the red meat diet, the participants consumed roughly the equivalent of 8 ounces of steak daily, or two quarter-pound beef patties. After one month on this diet, blood levels of TMAO were three times higher than when participants were on the diets based on either white meat or non-meat protein sources.
Half of the participants were also placed on high-saturated fat versions of the three diets. The diets all had equal amounts of calories. The researchers found that saturated fat had no additional effect on TMAO levels.
Importantly, the TMAO increases were reversible. When the participants discontinued the red meat diet and ate either the white meat or non-meat diet for another month, their TMAO levels decreased significantly.
“This study shows for the first time what a dramatic effect changing your diet has on levels of TMAO, which is increasingly linked to heart disease,” Hazen says.
“These findings reinforce current dietary recommendations that encourage all ages to follow a heart-healthy eating plan that limits red meat,” says nutrition researcher Dr. Charlotte Pratt, the NHLBI project officer for the study. “This means eating a variety of foods, including more vegetables, fruits, whole grains, low-fat dairy foods, and plant-based protein sources such as beans and peas.”