Study clarifies link between red meat consumption and cardiovascular health

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High consumption of red meat and processed meats is usually associated with harmful effects. They have also been classified by the International Agency for Research on Cancer as “probably carcinogenic” and “carcinogenic” to humans. They are also suspected of increasing cardiovascular risk, although the mechanisms involved in this case remain poorly understood. A new study confirms the harmful effects of animal proteins and explains how they contribute to atherosclerotic cardiovascular disease.

A better understanding of the consequences of meat consumption is especially important, especially for the elderly: in fact, this population group is much more vulnerable to heart disease and at the same time requires increased protein intake to compensate for the loss of muscle mass associated with age. Proteins are not only essential for good physical condition, they also help support the immune system. Thus, ANSES recommends that older people consume about one gram of protein per kilogram of body weight each day.

Why and how can eating meat, an important source of protein, be unhealthy? Recent studies have shown that certain metabolites created by bacteria in the gut microbiota when we eat meat may be responsible for the increased risk of cardiovascular disease. Researchers at Tufts University and the Cleveland Clinic Lerner Research Institute have been able to accurately identify the metabolites involved: trimethylamine-N-oxide (or TMAO) and its two key intermediates, gamma-butyrobetaine and crotonobetaine, which are themselves derivatives of L-carnitine, an amino acid that occurs naturally present in red meat.

Involvement of the gut microbiota

As part of their study, the researchers studied a sample of more than 3,900 people aged 65 years and older drawn from the National Institutes of Health’s Long-Term Heart Health Study of Americans. They analyzed their diet, noted several blood biomarkers, including the metabolites mentioned above, and observed the incidence of cardiovascular disease in this cohort. Participants were followed up for an average of 12.5 years.

The results confirm that increased consumption of red and processed meat is associated with a higher risk of atherosclerotic cardiovascular diseases (myocardial infarction, coronary heart disease, stroke, etc.): the risk increases by 22% with approximately 1.1 servings of meat per day.

They also found that about 10% of this risk was due to elevated 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 meat, by general inflammation (characterized by elevated levels of C-reactive protein); all of these biological pathways were more important than those associated with blood pressure or blood cholesterol levels. The team also states that consumption of fish, poultry and eggs “was not significantly associated” with an increase in the incidence of cardiovascular disease.

“The interplay between red meat, our gut microbiota, and the bioactive metabolites they produce appears to be an important risk pathway that creates a new target for possible interventions to reduce heart disease,” concludes Meng Wang, a researcher at the Friedman School of Nutrition. Science and Politics at Tufts University and first author of the study.

Three Main Pathways That Contribute to Increased Risk

Thus, this new study sheds light on three main ways in which red and processed meat increases the risk of cardiovascular disease: metabolites synthesized by the microbiome, blood sugar levels and general inflammation. Further research is needed to determine if these results can be generalized across ages and ethnicities, but these initial results already provide some insight into the diet older adults should follow to stay healthy.

“While more research is needed, the current report represents a potential new target for preventing or treating heart disease in a subset of people who consume excessive amounts of red meat,” said Ahmed Hasan of the National Heart’s Department of Cardiovascular Sciences. The Lung and Blood Institute, which was not involved in the study.

Please note that this study is part of a larger study by scientists at the Friedman School and the Cleveland Clinic that aims to shed light on the role of the gut microbiota in human health, specifically in cardiovascular disease. In the spring, a study published in JAMA Network Open was already pointing to a role for TMAO (and its associated metabolites) in increasing human mortality (regardless of whether death is due to cardiovascular or other diseases): people with the highest levels of TMAO had on 20-30% higher risk of death!

Fortunately, you can limit your TMAO levels by making dietary changes, such as limiting your intake of red and processed meats, and opting for other sources of protein (particularly plant-based proteins). At the same time, experts recommend eating foods that are known to be healthy for the heart (oilseeds, fruits and green vegetables, chocolate with a high cocoa content, tea, etc.).

M. Wang et al., Arteriosclerosis, thrombosis and vascular biology.

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