Eating red meat damages blood vessels! Harvard study finds 10 types of intestinal microbes that play a role

Red meat increases the risk of cardiovascular and cerebrovascular diseases. A recent study from Harvard University found that there are at least 10 types of microorganisms in the human intestine that can convert red meat into TMAO and promote the occurrence of diseases.

Red meat such as pork, beef and mutton are rich in choline, L-carnitine, betaine, etc. They can produce trimethylamine (TMA) under the action of intestinal flora and TMAO in the liver, thereby promoting the occurrence of cardiovascular and cerebrovascular diseases such as diabetes, obesity, atherosclerosis, and stroke.

Why do some people develop cardiovascular and cerebrovascular diseases while others do not, even though they eat the same meat?

Simply put, it's the bacteria that are different. If two people have the same eating habits but different intestinal microbial composition, their ability to produce TMAO will be different, and their risk of disease will be different. It has been proven that certain specific intestinal bacteria, such as Clostridium, can predict the level of TMAO in the blood.

To find the culprit for TMAO production, the researchers collected 925 stool samples and 473 blood samples over a six-month period.

The results showed that men with higher plasma TMAO levels were older, less physically active, had a higher BMI index, lower plasma high-density lipoprotein HDL-C levels, and consumed more red meat in their diet. They also had higher plasma TMA precursors choline and L-carnitine concentrations.

Moreover, both long-term and short-term red meat intake was positively correlated with plasma TMAO levels.

That is: the more red meat and choline you consume, the higher your TMAO level will be, but the lower the diversity of intestinal microorganisms will be.

After adjusting for confounding factors such as age, BMI, exercise, smoking, antibiotics, and probiotics, the researchers identified 10 bacterial species whose relative abundance was significantly associated with plasma TMAO concentrations, including:

8 Firmicutes: Clostridium citroniae, C. nexile, C. clostridioforme, Roseburia hominis, etc.;

1 Bacteroidetes: Alistipes shahii;

1 actinomycete: Eggerthella.

Among them, the relative abundance of 4 bacterial genera was greater than 0.1%, and the abundance of the remaining 6 genera was relatively low (0.005%-0.1%).

Is it really the flora that causes the difference?

To answer this question, they next used four intestinal bacterial genera that were highly correlated with TMAO production as grouping criteria and divided the participants into high-abundance and low-abundance groups. The results showed that only in the high-abundance group of TMAO-related bacterial genera, long-term dietary habits and short-term red meat intake were significantly correlated with plasma TMAO levels.

In other words, red meat will become harmful only if there are enough intestinal microorganisms that can produce TMAO.

Among these bacteria, Alistipes shahii, a genus highly associated with TMAO, significantly enhanced the association between red meat intake and cardiovascular metabolic risk markers.

This fungus is our main focus.

Through this study, we can basically conclude that:

The mechanism chain is red meat → intestinal bacteria → TMAO → cardiovascular disease.

Red meat increases plasma TMAO levels through specific intestinal flora, thereby increasing the risk of cardiometabolic diseases.

Do you think we should eat less red meat or kill those specific intestinal bacteria?

After reading this article, I wonder if the red meat on the plate will still taste delicious...

Li J, Li Y, Ivey KL, et al. Interplay between diet and gut microbiome, and circulating concentrations of trimethylamine N-oxide: findings from a longitudinal cohort of US men [published online ahead of print, 2021 Apr 29]. Gut. 2021;gutjnl-2020-322473.

doi:10.1136/gutjnl-2020-322473