Heart disease is the main cause of death in both the United States and the rest of the world. While age raises the risk of cardiovascular disease, including heart attacks and stroke, other risk factors are modified by lifestyle.

Consuming wholesome meals, especially fruits and vegetables, engaging in regular exercise, getting enough sleep, maintaining healthy body weight, quitting smoking, and managing high blood pressure, high cholesterol, and high blood sugar are all known to promote cardiovascular health.

But there are some foods that can increase the risk of cardiovascular disease.

And Red meat is one of them.

But, “most of the focus on red meat intake and health has been around dietary saturated fat and blood cholesterol levels,” says Meng Wang, Ph.D., co-lead author of the study and postdoctoral scholar at Tufts University’s Friedman School of Nutrition Science and Policy in Boston.

According to new findings published today in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, the increased risk of heart disease linked to red meat consumption may be partially explained by chemicals produced in the digestive tract by gut microbes after eating red meat.

“Based on our findings,” according to the author, “novel interventions may be helpful to target the interactions between red meat and the gut microbiome to help us find ways to reduce cardiovascular risk.”

But how does red meat affect our bodies?

Previous studies have identified a link between an increased risk of cardiovascular disease and specific metabolites, the chemical byproducts of food digestion. One of these metabolites is called TMAO, which stands for trimethylamine N-oxide. Gut bacteria make TMAO that helps break down L-carnitine-rich red meat.

Humans who have high blood levels of TMAO may have an increased risk of developing Type 2 diabetes, chronic renal disease, and CVD. But it is still not known if TMAO and related metabolites made from L-carnitine can help explain how eating red meat affects the risk of heart disease and how much they may contribute to the risk of heart disease caused by eating meat.

New Research

To answer these questions, researchers in this study analyzed blood samples for metabolite levels. Additionally, they looked into whether red meat consumption’s heightened cardiovascular risk could be attributed to blood sugar, inflammation, blood pressure, or blood cholesterol.

Nearly 4,000 of the 5,888 adults recruited for the Cardiovascular Health Study in 1989 and 1990 were included in the study. When they joined the CHS, an observational study of risk factors for cardiovascular disease in adults aged 65 or older, the people who were chosen for this study did not have any signs of cardiovascular disease.

The CHS follows 5,888 people from four cities: Sacramento, California, Hagerstown, Maryland, Winston-Salem, North Carolina, and Pittsburgh, Pennsylvania.

At the time of recruitment, participants had an average age of 73, were almost two-thirds female, and 88 percent of them self-identified as white.

Participants were followed up for an average of 12.5 years, although in some cases, it went as long as 26 years. Participants’ sociodemographic details, including household income, level of education, and age, were evaluated during the follow-up appointment, along with their medical history, lifestyle, and health conditions.

At the beginning of the trial and again in 1996-1997, several different blood biomarkers were evaluated and analyzed. The amounts of TMAO, gamma-butyrobetaine, and crotonobetaine, three gut-microbiome markers associated with red meat consumption, were measured in fasting blood samples maintained frozen at -80 °C.

All study participants additionally completed two validated food-frequency questionnaires regarding their typical eating habits, including consumption of red meat, processed meat, fish, poultry, and eggs, before the beginning of the study and once more between 1995 and 1996.

The first questionnaire asked participants to rate their frequency of eating specific amounts of different foods over the course of the previous 12 months, ranging from “never” to “almost every day or at least five times per week,” based on medium portion sizes that varied depending on the food source.

In the second questionnaire, there were ten frequency categories with standard serving sizes, ranging from “never or less than once per month” to “six+ servings per day.”

In the new analyses, the scientists examined the risk of cardiovascular disease among participants who consumed various amounts of meals with an animal source (i.e., red meat, processed meat, fish, chicken and eggs). 

The study found:

They discovered that consuming more meat, particularly red and processed meat, was associated with a 22 percent increased risk of atherosclerotic cardiovascular disease – a 22 percent increase for every 1.1 serving per day.

According to the scientists, a rise in TMAO and associated compounds identified in the blood accounted for nearly one-tenth of the increased risk.

They said that the pathways involved in blood sugar and systemic inflammation may contribute to the explanation of the associations between red meat consumption and cardiovascular disease.

Blood sugar and inflammation also seem to be more important in the link between eating red meat and heart disease than blood pressure or blood cholesterol.

Consumption of fish, poultry, and eggs was found to have no significant impact on cardiovascular disease risk.

“Research efforts are needed to better understand the potential health effects of L-carnitine and other substances in red meat such as heme iron,” adds Wang, “which has been associated with Type 2 diabetes, rather than just focusing on saturated fat.”

Limitations

Several limitations of the study may have affected its conclusions. Since the study was observational, it was unable to account for all cardiovascular disease risk variables and hence cannot conclusively establish a causal relationship between meat consumption and cardiovascular disease or the mediating role of chemicals produced by the gut microbiome.

In addition, food intake was self-reported, therefore reporting errors were possible. Furthermore, because the majority of the study participants were older, white men and women from the United States, the results might not be applicable to groups that are younger or more ethnically diverse.

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