Blood sugar, general inflammation, and microbiome-related metabolites like TMAO seem to be more crucial in regulating heart disease risk than blood pressure or cholesterol levels.
Is there a link between consuming more meat, particularly red and processed meat, and an increased risk of cardiovascular disease? If so, why? The effects of foods derived from animals on atherosclerotic cardiovascular disease (ASCVD) are hotly contested despite extensive research, and the mechanisms behind any possible impacts of animal proteins are still unknown. Understanding the effects of meat consumption is crucial for older adults since they are most at risk for heart disease and may benefit from consuming protein to counteract the deterioration of muscle mass and strength that comes with aging.
The link between heart disease and saturated fat, dietary cholesterol, sodium, nitrites, and even high-temperature cooking has been studied by scientists over the years, but the evidence for many of these mechanisms has not been strong. Recent data points to specific metabolites produced by our gut bacteria when we consume meat as the potential underlying culprits.
A recent study headed by scientists at the Cleveland Clinic Lerner Research Institute and the Friedman School of Nutrition Science and Policy at Tufts University quantifies the risk of ASCVD associated with meat consumption and identifies underlying biologic pathways that may explain this risk. The study of over 4,000 men and women over the age of 65 in the United States found that greater meat intake is associated with an increased risk of ASCVD—22 percent higher risk for every 1.1 serving per day—and that increased levels of three metabolites generated by gut bacteria from nutrients prevalent in meat explain roughly 10% of this increased risk. Red meat was associated with a higher risk and interconnections with gut bacterial metabolites, however, this was not found for poultry, eggs, or fish.
The research drew on years of data from the National Institutes of Health’s (NIH’s) Cardiovascular Health Study (CHS), a long-term observational study of risk factors for cardiovascular disease in Americans aged 65 and older. Several blood biomarkers were measured at baseline and again during follow-up, including levels of the gut-microbiome generated trimethylamine N-oxide (TMAO) and two of its key intermediates, gamma-butyrobetaine, and crotonobetaine, derived from L-carnitine, abundant in red meat.
Highlights
- In this community-based cohort of older U.S. men and women, higher intakes of unprocessed red meat, total meat (unprocessed red meat plus processed meat), and total animal source foods were prospectively associated with a higher incidence of ASCVD during a median follow-up of 12.5 years.
- The positive associations with ASCVD were partly mediated (8-11 percent of excess risk) by plasma levels of TMAO, gamma-butyrobetaine, and crotonobetaine.
- The higher risk of ASCVD associated with meat intake was also partially mediated by levels of blood glucose and insulin and, for processed meats, by systematic inflammation but not by blood pressure or blood cholesterol levels.
- Intakes of fish, poultry, and eggs were not significantly associated with ASCVD.
These findings help answer long-standing questions on mechanisms linking meats to the risk of cardiovascular diseases,” said the paper’s co-first author Meng Wang, a post-doctoral fellow at the Friedman School. “The interactions between red meat, our gut microbiome, and the bioactive metabolites they generate seem to be an important pathway for risk, which creates a new target for possible interventions to reduce heart disease.”
The 3,931 study subjects were followed for a median of 12.5 years, and their average age at baseline was 73. The study adjusted for established risk factors such as age, sex, race/ethnicity, education, smoking, physical activity, other dietary habits, and many additional risk factors.
“Interestingly, we identified three major pathways that help explain the links between red and processed meat and cardiovascular disease—microbiome-related metabolites like TMAO, blood glucose levels, and general inflammation—and each of these appeared more important than pathways related to blood cholesterol or blood pressure,” said co-senior author, Dariush Mozaffarian, dean for policy at the Friedman School. “This suggests that, when choosing animal-source foods, it’s less important to focus on differences in total fat, saturated fat, or cholesterol, and more important to better understand the health effects of other components in these foods, like L-carnitine and heme iron.”
