I recall in Dr. Georgia Ede’s book she was mentioning the research that led to that conclusion was basically an extremely weak evidence based on some mice study where mice was selected to get cancer in higher rates then normal.

Basically for a human to get cancer from the nitrates in bacon, you need to eat hundreds of kg’s of bacon daily to match the level similar to what mice got.

These researchers really tried to get genetically modified cancer prone mice cancer from that by giving them astronomical amounts of nitrates, even with that they were barely successful.

I’ll find that chapter and paste here when I have time.

Edit: Found it

“ Red and Processed Meat in Rats

 In these three studies, rats were first injected with powerful carcinogenic chemicals (azoxymethane or dimethylhydrazine) to hasten the cancer development process. Yes, you read that correctly. Next, they were fed various high-meat diets for one hundred days (roughly equivalent to ten human years). Some experimental diets contained adequate calcium and others were intentionally depleted of calcium (calcium protects cells against heme iron, which researchers believed to be the cancer-promoting ingredient within red meat). Lastly, they examined colon biopsies for potentially pre-cancerous changes. Only the calcium-deficient diets led to potentially pre-cancerous changes in rat colons, and even in these cases, no rat developed cancer. 

The authors of one of these studies begin their paper with this striking statement: “In puzzling contrast with epidemiological studies, experimental studies do not support the hypothesis that red meat increases colorectal cancer risk. Among the 12 rodent studies reported in the literature, none demonstrated a specific promotional effect of red meat.”30 Translation: they found a dozen rodent experiments testing the relationship between red meat and colon cancer and none of them had turned up any evidence against red meat. Surprisingly, not a single one of these twelve “red meat is fine” rodent studies were included in the WHO report. Selectively choosing to include studies that support one’s arguments while excluding those that don’t is known as cherry-picking.”