Thursday, October 29, 2015

Saving Your Bacon Op Ed in the SF Chronicle


Peter Hertzmann said...

I agree with everything you say in your editorial, although a few things I may have stated differently. My problem with it is that I feel you missed the whole point of this circle-jerk caused by the IARC decision to classify processed meat as a Group 1 substance combined with a lazy news media looking for sensational headlines.

The IARC news release along with the "paper" they published in Lancet says that by placing processed meat into Group 1 that "processed meat probably causes cancer in humans". That statement, in and by itself, makes about as much sense as saying "living probably causes death". Their definition of processed meat is so broad that essentially any meat that is not fresh is declared processed. It doesn't matter whether chemicals are aded or not. Saying a substance causes cancer without stating all the relevant details about the cancer is also meaningless. What type of cancer? Is it treatable? Is it slow or fast growing? Is it more prevalent in different parts of the world? Is it detectable at an early stage? And it would be nice if the IARC defined what they mean by "probably".

Looking at the types of studies used to determine the IARC's conclusion, one finds that only about half the studies found a correlation between processed meats and colorectal cancer. These studies were generally epidemiological studies based on self reporting and cohort studies where a lot of statistical games are played to squeeze out the results from the data. The committee of "experts" apparently decided that the "positive" studies outweighed the "negative" studies to show that processed meat "probably" causes cancer. The article fails to disclose the votes of the experts. In the past, these decisions have been anything but unanimous.

In the Lancet article, the general cancer type identified is colorectal cancer. They state that their data shows that there is an increased chance of 18% when 50 grams of processed meat is consumed each day. What does that mean? According to the National Cancer Insitute, you currently have about a 4.5% chance of contracting a colorectal cancer in your lifetime. Your excessive consumption of bacon will cause your lifetime chance to increase to 5.3%. Another way of looking at it is that the number of new cases of colon and rectum cancer is 42.4 per 100,000 men and women per year. The number of deaths is 15.5 per 100,000 men and women per year. By eating processed meats, the numbers increase to 50.0 and 18.3, respectively. This, of course, is not what the media is reporting because the analysis is too wonky and the details are too involved for the reporters/editors.

In the end, the whole brouhaha is really a matter of how probable is probably. (And you probably should have a regular colonoscopy.)

Ken Albala said...

Yes of course! Thanks Peter. I only had 700 words!!