The notion that red meat causes cancer is one that many people ask me about.
Since I advocate eating meat, people wonder whether this would raise their cancer risk.
What does the evidence say?
First, let’s look at the quality of the evidence.
The evidence used by the WHO is epidemiological evidence.
This is the type of evidence that looks at large numbers of people and their characteristics – such as whether they eat a lot or a little meat – and sees who becomes ill, and who remains healthy.
As such, epidemiology cannot prove that the characteristics of these people causes ill health.
It can only show association.
Now, the great triumph of epidemiology in the last century was that it showed that cigarette smoking causes lung cancer.
Strictly speaking, it still didn’t show causation, but the difference between smokers and non-smokers in ling cancer rates was so huge that it left little room for doubt.
Cigarette smokers got lung cancer at rates of from 9 to 25 times higher than non-smokers.
There’s very little that could explain that fact other than cigarettes cause cancer.
This in turn led to the Bradford Hill criteria for epidemiology, which Sir Austin Bradford Hill, an epidemiologist, formulated in 1965.[i]
Bradford Hill’s number one criterion was the strength of the association, such as that between cigarettes and lung cancer.
Bradford Hill noted that in the 19th century, it was discovered that chimney sweeps had a higher incidence of scrotal cancer.
The incidence of scrotal cancer among chimney sweeps was 200 times higher than that of others.
With numbers that high, there can be little doubt as to causation.
Bradford Hill’s other criteria included consistency, specificity, plausibility, and others.
Now, what kind of association do we see between red meat and cancer?
The World Health Organization cites relative risks of 1.17 to 1.18.[ii]
That is tiny, and doesn’t even come close to causation.
Then there’s the issue of consistency. Some studies have found no increased risk for meat and cancer.[iii]
“…the currently available epidemiologic evidence is not sufficient to support an independent positive association between red meat consumption and colorectal cancer.”
Another issue is that of absolute risk.
Suppose the connection between red meat and cancer were true.
The lifetime risk of getting colon cancer is about 4.5%, so a relative risk of 1.17 raises the absolute risk to 5.3%.
Trivial, in my opinion.
People who have eaten lots of meat in the past several decades have done so in the face of advice not to do so.
Mainstream health organizations have urged us not to eat meat because the saturated fat in it is allegedly bad for us. (It isn’t, but that’s another discussion.)
People who followed that advice are likely to be more health conscious than people who ignored it.
Those who followed the advice are likely to have exercised more, maintained a normal body weight, did not drink to excess, ate less ultra-processed and fast foods, etc.
And people who ignored that advice were likely, on average, to be less health conscious.
Given these considerations, the evidence is very weak. It shows a tiny increase in risk, and is not consistent.
It doesn’t even come close to showing that red meat causes cancer.
Personally, I’m going to ignore it.
Any epidemiology study that shows less than double the risk is highly suspect. (Some say less than 5 times the risk.)
There’s no doubt in my mind that red meat does not cause cancer.
What does cause colon cancer?
One study found that visceral fat, the type of fat found around the abdomen and that’s linked to insulin resistance and the metabolic syndrome, was highly associated with colon cancer.
People in the highest third of visceral fat had 6 times the rate of colon cancer.[iv]
That’s a strong association.
Bottom line: red meat is part of a healthy diet.
Peace and health.
[i] Fedak, Kristen M., et al. "Applying the Bradford Hill criteria in the 21st century: how data integration has changed causal inference in molecular epidemiology." Emerging themes in epidemiology 12.1 (2015): 14.
[ii]
https://www.ft.com/content/42259e20-92b5-11e5-bd82-c1fb87bef7af
[iii] Alexander, Dominik D., and Colleen A. Cushing. "Red meat and colorectal cancer: a critical summary of prospective epidemiologic studies." Obesity reviews 12.5 (2011): e472-e493.
[iv] Yamamoto, Shuichiro, et al. "Visceral fat area and markers of insulin resistance in relation to colorectal neoplasia." Diabetes care 33.1 (2010): 184-189.
