Why is red meat consumption associated with an increased risk of colorectal cancer? Since 2015, the International Agency for Research on Cancer (CIRC) classifies red meat as “probably carcinogenic“But due to lack of biological evidence, there is still no scientific consensus on the subject.

A new study published on June 17 in the journal Cancer Discovery could be a game-changer. According to researchers from Harvard University who signed this publication, a diet very rich in red meat is indeed the cause of specific damage to the DNA of consumers.

900 DNA sequenced

How could they have drawn this conclusion? So far, studies have established a correlation between red meat and cancer by questioning a posteriori people with colorectal cancer about their eating habits. A rather weak method which does not allow to explain the phenomenon.

In this new study, the researchers went further: they sequenced the DNA of colon cells in 900 patients with and without colorectal cancer.

These patients, recruited from cohorts of scientific studies of 280,000 people, had informed their eating habits since the start of their follow-up. By crossing all this data, the researchers were able to compare the DNA analyzes and the lifestyle of the participants.

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A specific mutation

Result: The analyzes revealed a specific type of DNA mutation called alkylation, which had never been identified before.

Not all cells containing these mutations will necessarily become cancerous, and they were also present in healthy samples. But this mutation was significantly associated with eating red meat – both processed and unprocessed – before the onset of the disease.

In contrast, it was not associated with the consumption of poultry, fish, or other non-food factors, such as smoking or physical activity.

Identify patients at risk

And this is chemically explained: the chemical compounds present in red or processed meat, such as those produced from iron or nitrates, can cause these famous alkylations.

For the researchers, this discovery could therefore help doctors identify the patients most genetically at risk of cancer, to encourage them to limit their consumption of red meat.

Evaluate life expectancy

Last point revealed by the study: patients whose tumors had the highest level of alkylation had a 47% more risk of dying from them.

If the level of alkylation is indeed a marker of disease severity, it could be used to provide a prognosis on the life expectancy of patients.

Finally, understanding this mechanism opens the way to the development of new treatments capable of interrupting or even reversing this modification of DNA.

No more than 500 grams per week

In the meantime, should we ban red meat? Not according to these researchers, who show that the high levels of alkylation were only observed in the tumors of patients consuming on average more than 150 grams of red meat per day.

A moderate consumption of meat, associated with a balanced diet, therefore remains the recommendation in force.

For Public health France, do not exceed 500 grams of red meat and 150 grams of cold meats per week and favor other sources of protein such as poultry, fish and vegetable proteins.