The link between colon cancer and meat consumption has been trumpeted by vegetarians and heatedly refuted by paleo fanatics. My question, as usual, is: “What role does genetics play?”
The World Health Organization includes processed meat on their list of probable carcinogens, based on several large epidemiological studies. According to the American Cancer Society, the lifetime risk of colon cancer is around 5%, and increasing that risk by around 20% would give a lifetime risk of about 6%.
A 2014 study looked at the interaction between genetics and the risk of colon cancer from processed meat. The study was conducted with over 9,000 people with colon cancer who were compared to 9,000 control subjects without colon cancer. The study found that the increased risk of colon cancer from meat consumption was limited to those with a certain genetic variant in the GATA3 gene.
- TT: higher risk of colon cancer with increasing meat consumption
- GT: higher risk of colon cancer with increasing meat consumption
- GG: normal
The increase in the risk of colon cancer for those with the T allele did vary by the amount of meat consumed. Those with the highest consumption of meat and a T allele were at a 39% increased risk for colon cancer, while those with lower meat consumption were at a 20 – 26% increase in risk.
People who carry the GG genotype, which is about 60% of Caucasians and 90% of Chinese populations, were not found to have an increased risk of colon cancer with meat consumption. This actually makes sense with the population-wide studies that showed Americans to be at an 18% increased risk of cancer with meat consumption –without breaking it down by genetic differences. I think this is a great example of why dietary recommendations based on population-wide studies are often only applicable to a portion of the population.
For those of you who want to get geeky with the genetics, here is a description from the study on the function of the GATA3 gene:
GATA3 has long been associated with T cell development, specifically Th2 cell differentiation . GATA3 is up-regulated in ulcerative colitis , which is associated with increased risk of colorectal cancer . However, the role of GATA genes as transcription factors extends to epithelial structures with a known role in breast, prostate and other cancers –. GATA factors are involved in cellular maturation with proliferation arrest and cell survival. Loss of GATA genes or silencing of expression have been described for breast, colorectal and lung cancers .
Finally, just for all the Parks and Recs fans who always think of Ron Swanson when they hear the word ‘meat’: