Transcript: Solving a Colon Cancer Mystery
Colorectal cancer is the second leading cause of cancer death in the United States, after lung cancer. If you look at the rates of lung cancer around the world, they vary by a factor of 10. If there were nothing we could do to prevent lung cancer, if it just arose spontaneously, happened at random, you’d assume that the rates everywhere would be the same. But since there’s such a huge variation in rates, you assume there’s some external cause, and indeed, we now know smoking is responsible for 90% of lung cancer cases. So if we don’t want to die of the #1 cancer killer, by just not smoking we can throw 90% of our risk out the window. For colon cancer, there’s an even bigger spread. So it appears colon cancer doesn’t just happen; something makes it happen. Well, if our lungs can get filled with carcinogens from smoke, maybe our colons are getting filled with carcinogens from food. Researchers from the University of Pittsburgh and the University of Limpopo sought to answer the question, “Why do African Americans get more colon cancer than native Africans?" Why study Africans? Because colon cancer is extremely rare in native African populations, like more than 50 times lower than rates of Americans, white or black.
It’s the fiber, right? Dr. Burkitt was the first to describe the low incidence of colon cancer in native Africans, ascribing it to their traditional staple diet that was high in whole grains and, therefore, fiber content. Seems you get about a 10% reduction in risk for every 10 grams of fiber a day. So hey, if it’s a 1% drop for each gram, and they’re eating upwards of 100 grams a day, that could explain why colon cancer is so rare in sub-Saharan Africa.
But wait a second, the modern African diet is highly processed and low in fiber, and yet there has been no dramatic increase in colon cancer incidence.
The modern African diet has a low fiber content, as most populations now depend on commercially produced refined cornmeal. And we’re not just talking low fiber intake; we’re talking United States of America low, down around half the recommended daily allowance. Yet colon disease still remains rare; still 50 times less colon cancer.
Maybe it’s because they’re thinner and exercise more? No, they’re not, and no, they don’t. If anything, their physical activity levels may now be even lower. So if they’re sedentary like us, eating mostly refined carbs, few whole plant foods, little fiber—like us–why do they have 50 times less colon cancer? Well, there is one difference. The diet of both African-Americans and Caucasian-Americans is rich in meat, whereas the native African diet is so low in meat and saturated fat they have total cholesterol levels averaging 139, compared to over 200 in the U.S.
So yes, they don’t get a lot of fiber anymore, but they continue to minimize meat and animal fat consumption, supporting evidence that perhaps the most powerful determinants of colon cancer risk are the levels of meat and animal fat intake. So why do Americans get more colon cancer than Africans? Maybe the rarity of colon cancer in Africans is not the fiber, but their low animal product consumption.
There is a divergence of opinion as to whether it’s the animal fat, cholesterol, or animal protein that is most responsible for the increased cancer risk, as all three have been shown to have carcinogenic (cancer-causing) properties, but it may not really matter which component is worse, as a diet rich in one is usually rich in the others.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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