Research has now found more evidence that Western diets that include high levels of red or processed meats, sugars, and processed carbohydrates can lead to an increased risk of colorectal cancer because of how gut microbes respond to that food. In a new study reported in Gastroenterology, researchers analyzed information about dietary intake, health data, and samples from over 134,000 volunteers from studies in the United States. The researchers also assessed DNA that was isolated from strains of Escherichia coli that were found in over 1,000 colorectal tumors.
The scientists were looking for a specific genetic feature in the genomes of the E. coli. This feature was a genetic island called polyketide synthase (pks), which encodes for an enzyme that has been found to cause genetic mutations in human cells. Genetic islands are pieces of bacterial DNA that can be shared among bacteria, and they are accessories to the core microbial genome. Mutations in human DNA may sometimes lead to cancer, depending on where those mutations occur.
The investigators determined that western diets were linked to colorectal tumors that carried high levels of pks+ E. coli, but this association was not found among tumors with low levels or an absence of pks+ E. coli.
“These findings support our hypothesis that Western-style diets increase colorectal cancer risk through its effect on pks+ E. coli,” said corresponding study author Shuji Ogino, MD, PhD, MS, of the Brigham and Women's Hospital.
“This is the first study to link Western diet with specific pathogenic bacteria in cancer. Our next question is which component of western-style diet and lifestyle relates to colorectal cancer containing this bacterial species.”
There is an abundance of evidence that links red meat consumption with an increased risk of some types of cancer, especially colon cancer. The International Agency for Research on Cancer (IARC) has found that red meat is probably carcinogenic to people. Red meat includes beef, pork, lamb, and goat. The IARC has said that processed meats, including foods like bacon, hot dogs, ham, and sausage, are carcinogens on the level of alcohol and tobacco.
Certain chemicals that are used to cure processed meats, such as nitrates, are converted into carcinogens by the human body. Other research has suggested, however, that microbes in the human gastrointestinal tract metabolize red meats in a way that produces carcinogens. This work has provided yet another mechanistic link between colorectal cancer and diet.
Sources: Brigham and Women's Hospital, Gastroenterology