The intake of red and processed meat has often been linked to an increased risk of cardiovascular diseases, but maybe it is not that simple?

Research results point in different directions, which may be explained by other factors in our lifestyle than our meat intake alone.

Researchers from the Department of Food Science, Aarhus University and their colleagues from Ghent University in Belgium have come a step closer to understanding the connection between how our meat intake affects us, and what else we put on our plate on a daily basis.

This has been done by examining the effect of four dietary patterns on a compound called trimethylamine N-oxide (TMAO). TMAO is formed in the liver from trimethylamine (TMA), which is formed by intestinal bacteria from carnitine and choline – which is found especially in meat from four-legged animals.

Previous studies have indicated that TMAO can cause atherosclerosis, and therefore a low level of TMAO is thought to be desirable. 

What else we eat matters

The researchers have looked examined how the intake of either chicken or a combination of red and processed meat affects the TMAO level of pigs fed either a typical Western diet with a high fat content and a low vegetable content - or fed a somewhat healthier diet with a high fiber content and a high content of vegetables.

The feeding took place over four weeks, and 32 pigs were included in the study, where researchers both examined the TMAO level in the pigs’ urine and looked closely at the TMAO-related gene expression in the liver – i.e. the processes in the liver, where specific genes are activated to affect the capacity for TMAO formation. In addition, the researchers also investigated whether correlations exist between the TMAO level in the urine and the various bacteria present in the gut.

The results show that our dietary pattern has a significant impact on the TMAO level.

Hanne Christine Bertram, Professor at the Department of Food Science at Aarhus University and one of the researchers behind the study, elaborates:

- We have observed a lower TMAO level in the urine of pigs fed red and processed meat with an otherwise high-fiber diet with a high content of vegetables compared to the cases, in which the pigs, together with the red and processed meat, were fed a diet with a higher fat content and refined sugar and a low content of vegetables. This shows us that there is a link between the amount of TMAO that is formed, when we eat red and processed meat, and what we otherwise eat. On the other hand, we find no effect of the different dietary patterns of the pigs fed chicken instead of red and processed meat.

Intestinal bacteria may be the explanation

The researchers have also tried to find an explanation for the reason why the different dietary patterns affect the TMAO levels in varying ways.

The study found no correlation between the different dietary patterns and gene expression in the liver. On the other hand, correlations were found between the TMAO level in the pig’s urine and the composition of the pig’s intestinal bacteria:

- We found that a higher level of, among other things, Firmicutes bacteria in the intestine is associated with a higher TMAO level in the urine, which we did not observe for Bacteroidetes bacteria. It is a correlation, which is consistent with previous studies that have shown an increased level of Firmicutes bacteria compared to Bacteroidetes bacteria in high TMAO production. However, it has not yet been proven that these correlations between the number of specific bacteria and the TMAO level are also the direct cause of the formation of TMAO, says PhD student on the project, Rebekka Thøgersen.

- First and foremost, our results show that the amount of TMAO that we produce, when we eat red and processed meat, is affected by the rest of our diet. Therefore, if we assume that TMAO reflects an increased risk of cardiovascular disease, our results indicate that eating red and processed meat does not have to be harmful if we otherwise eat healthily. Apparently, the regulation does not occur in the liver, which is otherwise involved in TMAO formation. Instead, it indicates that the rest of our diet exerts influence through changes in the composition and activity of the intestinal bacteria, Hanne Christine Bertram adds and concludes:

- We have come a step closer to understanding the processes that affect our TMAO level, when we eat meat - and thus our risk of getting cardiovascular disease.        

• Read more: Beef can lower your blood pressure 

About the research