Your gut may be telling you to eat less meat and more plant foods — literally. A substance produced in the gut as a by-product of the digestion of animal products may build up in the blood and be a key player in your risk for heart attack or coronary heart disease, suggests a new study.

The microbes that live in our digestive tract play an important role in the absorption of nutrients, metabolism, energy levels and our immune response. When we digest nutrients found in animal products, like red meat, a substance known as trimethylamine N-oxide (TMAO) is produced in the gut. High levels of TMAO have been linked to heart attack and heart disease.

The largest increases in TMAO resulted in a 67 percent higher risk of heart disease.

Researchers from several universities and medical schools, including Tulane University, Harvard Medical School and Harvard T.H. Chan School School of Public Health, studied the diets, physical activity and smoking status of 760 women, aged 30 to 55, who participated in the Nurses’ Health Study. The researchers chose 380 women with heart disease along with 380 demographically similar women who did not have heart disease for the study.

Two blood samples measuring levels of TMAO were taken 10 years apart. During the first blood collection, there were no differences found in TMAO levels between the women with heart disease and those without. Ten years later when the second blood sample was collected, TMAO levels were higher in the women with heart disease.

The risk of developing heart disease was determined by changes in TMAO levels in the women’s bodies during the ten-year follow-up period. Divided into three TMAO levels, every increase (to a higher TMAO level) increased the risk of heart disease by 23 percent.

The women who developed heart disease not only had higher levels of TMA, but also higher body mass index, a family history of heart attack, and they did not follow a healthy diet, described as higher intake of vegetables and lower intake of animal foods. The largest increases in TMAO resulted in a 67 percent higher risk of heart disease among the women.

“Diet is one of the most important modifiable risk factors to control TMAO levels in the body,” said researcher, Lu Qi of Tulane University, in a statement. He explained that the study’s findings suggest that lowering TMAO levels could help reduce the risk of heart disease and that gut-microbiomes may be a new area of study for heart disease prevention.

Plant-based diets continue to earn praise for lowering the risk of heart disease along with other chronic diseases. If you are looking to move toward a more plant-based diet, you might be interested in either the Mediterranean Diet or the DASH diet. Both emphasize fruits, vegetables, whole grains, nuts, poultry, fish and low-fat dairy foods, and both have been found to offer protection from heart disease.

The study is published in the Journal of the American College of Cardiology.