High consumption of red meat and processed meat is generally associated with deleterious effects. They have also been respectively classified as “probably carcinogenic” and “carcinogenic” for humans by the International Agency for Research on Cancer. They are also suspected of increasing cardiovascular risk, although the mechanisms involved in this case remain poorly understood. A new study confirms the harmful impact of animal proteins and explains how they contribute to the onset of atherosclerotic cardiovascular diseases.
A better understanding of the consequences of meat consumption is particularly important, especially in the elderly: in fact, this population is much more vulnerable to heart disease and at the same time requires an increased protein intake to compensate for the muscle losses associated with age. Not only are proteins essential for good physical condition, but they also help to maintain the immune system. ANSES thus recommends that seniors should take in around one gram of protein per kilo of body weight each day.
Why and how can eating meat — an important source of protein — be harmful to health? Recent studies have suggested that certain metabolites, created by bacteria in the gut microbiota when we eat meat, may be the cause of the increased cardiovascular risk. Researchers from Tufts University and the Cleveland Clinic Lerner Research Institute have succeeded in precisely identifying the metabolites involved: trimethylamine-N-oxide (or TMAO) and two of its key intermediates, gamma-butyrobetaine and crotonobetaine — themselves derived from L-carnitine, an amino acid naturally present in red meat.
The intestinal microbiota implicated
As part of their study, the researchers looked at a sample of more than 3,900 people, ages 65 and older, drawn from the Long-Term Study of the Heart Health of Americans conducted by the National Institutes of Health. They analyzed their diet, noted several blood biomarkers – including the metabolites mentioned above – and observed the incidence of cardiovascular disease within this cohort. Participants were followed for a median of 12.5 years.
The results confirm that an increased consumption of red and processed meat is linked to a higher risk of atherosclerotic cardiovascular diseases (myocardial infarction, coronary heart disease, stroke and others): the risk increases by 22% for approximately 1.1 portion of meat per day.
They further found that regarding 10% of this risk was due to increased levels of TMAO, gamma-butyrobetaine and crotonobetaine. This higher risk associated with meat consumption was also partly mediated by blood glucose and insulin levels and, for processed meats, by general inflammation (characterized by increased C-reactive protein levels); these biological pathways were all more important than those related to blood pressure or blood cholesterol levels. The team also states that the consumption of fish, poultry and eggs “was not significantly associated” with an increased incidence of cardiovascular disease.
« Interactions between red meat, our gut microbiota, and the bioactive metabolites they generate appear to be an important pathway of risk, creating a novel target for potential interventions to reduce heart disease. », concludes Meng Wanga researcher at the Friedman School of Nutrition Science and Policy at Tufts University and first author of the study.
Three main pathways that contribute to increased risk
In summary, this new study sheds light on three main pathways through which red and processed meat increases cardiovascular risk: metabolites synthesized by the microbiome, blood sugar and general inflammation. Further studies are needed to determine whether these findings are generalizable across ages and nationalities, but these initial findings already provide some insight into the diet older people should adopt to stay healthy.
« Although more studies are needed, the current report provides a potential new target for preventing or treating heart disease in a subgroup of people who consume excessive amounts of red meat. said Ahmed Hasan, from the Department of Cardiovascular Sciences at the National Heart, Lung, and Blood Institute, who was not involved in the study.
Note that this research is part of a larger study, led by scientists from the Friedman School and the Cleveland Clinic, aimed at shedding light on the role of the intestinal microbiota in human health, in particular in cardiovascular health. In spring, a study published in JAMA Network Openhad already pointed out the role of TMAO (and associated metabolites) in the increase in human mortality (whether the death is linked to a cardiovascular disease or to another disease): individuals with the highest levels high TMAO had a 20 to 30% higher risk of death!
Fortunately, it is possible to limit your TMAO level by modifying your diet, in particular by limiting your consumption of red and processed meat and by favoring other sources of protein (vegetable proteins in particular). At the same time, specialists recommend consuming foods known to be healthy for the heart (oilseeds, fruits and green vegetables, chocolate with a high cocoa content, tea, etc.).