176 THE CHINA STUDYmors are related to polyps, most scientists would agree^88 ,89 that they share
similar dietary associations and genetic characteristics. Those people who
have noncancerous problems in the large bowel, such as polyps, often are
the same people who later develop cancerous tumors.
So getting screened for polyps or other problems is a reasonable
way to establish risk for large bowel cancer in the future. But what if
you have a polyp? What is the best thing to do? Will surgical removal
of the polyp lessen colon cancer risk? A nationwide study has shown
that, when polyps were removed, there was a 76-90% decrease in the
expected cases of colon cancer,89,90 This certainly supports the idea of
routine screening.^89 , 91 It is commonly recommended that people get a
colonoscopy once every ten years starting at the age of fifty. If you have
a higher risk of colorectal cancer, it is recommended that you start at the
age of forty and screen more frequently.
How do you know if you are at a higher risk for colorectal cancer? We
can very roughly assess our personal genetic risk in several ways, We
can consider the probability of our getting colon cancer based on the
number of immediate family members who already have the disease, we
can screen for the presence of polyps, and we now can clinically test for
the presence of suspect genes.^92
This is an excellent example of how genetic research can lead to a bet-
ter understanding of complex diseases. However, in the enthusiasm for
studying the genetic basis for this cancer, two things often get overlooked.
First, the proportion of colon cancer cases attributed to known inherited
genes is only about 1_3%.89 Another 10-30%89 tend to occur in some
families more than others (called familial clustering), an effect possibly
reflective of a significant genetic contribution. These numbers, however,
exaggerate the number of cancers that are solely "due to genes."
Except for the very few people whose colon cancer risk is largely
determined by known inherited genes (1-3%), most of the family-con-
nected colon cancer cases (i.e, the additional 10-30%) are still largely
determined by environmental and dietary factors. After all, place of resi-
dence and diet are often shared experiences within families.
Even if you have a high genetic risk, a healthy plant-based diet is
capable of negating most, if not all, of that risk by controlling the ex-
pression of these genes. Because a high-fiber diet can only prevent colon
cancer-extra fiber won't ever promote colon cancer-dietary recom-
mendations should be the same regardless of one's genetic risk.