The link between colon cancer and meat consumption has been trumpeted by vegetarians — and refuted by paleo fanatics.
My question, as usual, is: “What role does genetics play?”
The World Health Organization includes processed meat on its list of probable carcinogens. This is based on several large epidemiological studies that show processed meat consumption increases colon cancer risk by 18-20%!
Putting the statistics into perspective:
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%.
This statistical risk is based on epidemiologic studies of the population as a whole and doesn’t take into account individual genetic variants that can increase – or decrease – the risk of colon cancer.
It turns out that for some people, meat consumption doesn’t increase the risk of colon cancer at all. For other people, the increase in risk is higher than the 20% increase.
A 2014 study looked at the interaction between genetics and the risk of colon cancer from processed meat. Researchers examine the genes of 9,000 colon cancer patients and 9,000 control subjects without colon cancer.
Researchers discovered the increase in colon cancer was linked to the GATA3 gene. This gene codes for a transcription factor involved in inflammation and blood vessel epithelial cells. High processed meat consumption in people with GATA3 genetic variants increased colon cancer cases.[ref]
Check your genetic data for rs4143094 (23andMe v5; AncestryDNA):
Check your genetic data for rs1269486 (23andMe v4; AncestryDNA):
The increase in the risk of colon cancer for those with the risk allele did vary by the amount of meat consumed. Carriers of the risk allele who ate the highest percentage of meat had a 39% increased risk for colon cancer; carriers who ate less meat were at a 20 – 26% increase in risk.
People who carry the normal 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.
Statistically, this actually makes sense with the population-wide studies that showed Americans overall to be at an 18% increased risk of cancer with meat consumption. And this is why population-wide recommendations for the diet are often misleading — or completely wrong.
Another study on the link between colon cancer and processed meat consumption found that the CCAT genetic variant also comes into play with meat consumption and colon cancer.
In general, carrying the rs6983267 T allele is associated with a lower risk of colon cancer (and even lower yet in people who regularly take aspirin). [ref][ref] But when looking at processed meat consumption of over 25 g/day, the decrease in risk for T allele carrier was eliminated. [ref]
This is a case where diet eliminates a natural protection against colon cancer.
Check your genetic data for rs6983267 (23andMe v4, v5; AncestryDNA):
If you carry the risk alleles – especially if you have a family history of colon cancer – consider cutting down on the processed meats.
Examples of processed meats include:
Instead, opt for some veggies along with meat or protein sources that aren’t fermented, smoked, or processed in other ways.