Chemicals produced in the digestive tract by gut microbes after eating red meat may help explain some of the increased risk of cardiovascular disease (CVD) associated with eating this food, according to new research published in the scientific journal Arteriosclerosis. Thrombosis, and Vascular Biology’.
Worldwide, cardiovascular diseases are the leading cause of death. Although the risk of developing cardiovascular disease, including heart attack and stroke, increases with age, other risk factors are influenced by lifestyle.
Lifestyle and behaviors known to improve cardiovascular health include eating healthy foods, especially fruits and vegetables; regular physical activity; get enough sleep; maintain a healthy body weight; give up smoking; and control high blood pressure, high cholesterol, and blood sugar.
“Most of the attention paid to red meat intake and health has focused on dietary saturated fat and blood cholesterol levels. Based on our findings, novel interventions may be helpful in targeting interactions between red meat and the gut microbiome to help us find ways to reduce cardiovascular risk,” said study co-author Dr. Meng Wang, a postdoctoral fellow in the Friedman School of Nutrition Science and Policy at Tufts University. from Boston.
Previous research has found that certain metabolites (chemical byproducts of food digestion) are associated with an increased risk of cardiovascular disease. One of these metabolites is TMAO, or trimethylamine N-oxide, which is produced by gut bacteria to digest red meat that contains high amounts of the chemical L-carnitine.
Elevated levels of TMAO in the blood of humans may be associated with an increased risk of CVD, chronic kidney disease, and type 2 diabetes. However, it remains unknown whether TMAO and related metabolites derived from L-carnitine may help explain the effects of red meat intake on cardiovascular risk, and to what extent they may contribute to cardiovascular risk associated with meat consumption.
To understand these questions, the researchers who conducted this study measured the levels of the metabolites in blood samples. They also examined whether blood sugar, inflammation, blood pressure and blood cholesterol can explain the elevated cardiovascular risk associated with red meat consumption.
Study participants were nearly 4,000 of the 5,888 adults initially recruited between 1989 and 1990 for the US Cardiovascular Health Study. Participants selected for the present study were free of clinical cardiovascular disease at the time of enrollment.
The median age of participants at enrollment was 73 years old, nearly two-thirds of participants were female, and 88 percent of participants identified as white. The median follow-up time of the participants was 12.5 years, and up to 26 years in some cases.
Participants’ medical history, lifestyle, health conditions, and sociodemographic characteristics, such as family income, education, and age, were assessed at follow-up appointments.
Various blood biomarkers were measured at the start of the study and again in 1996-1997. Fasting blood samples stored frozen at -80°C were tested for levels of several gut microbiomes associated with red meat consumption, including TMAO, gamma-butyrobetaine, and crotonobetaine.
In addition, all study participants responded to two validated food frequency questionnaires about their usual eating habits, including intake of red meat, processed meat, fish, poultry, and eggs, at the start of the study and again between 1995 and 1996. .
In the first questionnaire, participants indicated how often, on average, over the past 12 months they had eaten certain amounts of various foods, ranging from “never” to “almost every day or at least five times a week,” based on sizes average portion sizes, which varied depending on the food source.
In the second questionnaire, a frequency of ten categories of mean intake in the past 12 months was used, ranging from “never or less than once a month” to “more than six servings per day”, with defined standard serving sizes.
For the analyses, the researchers compared the risk of cardiovascular disease among participants who ate different amounts of animal-based foods (ie, red meat, processed meat, fish, chicken, and eggs).
What did they discover?
They found that eating more meat, especially red meat and processed meat, was linked to a higher risk of atherosclerotic cardiovascular disease — a 22 percent increased risk for every 1.1 servings a day.
According to the authors, the increase in TMAO and related metabolites found in the blood accounted for about a tenth of this elevated risk. They also noted that blood sugar and general pathways of inflammation may help explain the links between red meat consumption and cardiovascular disease.
Blood sugar and inflammation also appear to be more important in the link between red meat consumption and cardiovascular disease than pathways related to blood cholesterol or blood pressure. Fish, poultry, and egg consumption were not significantly associated with an increased risk of cardiovascular disease.
“Research is needed to better understand the potential health effects of L-carnitine and other substances in red meat, such as heme iron, that have been associated with type 2 diabetes, rather than focusing solely on the saturated fats,” says Wang.