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A low-fat, high-fiber diet is often recommended
as a way of preventing polyps in the lining of the colon -- growths associated
with an increased risk of colon cancer. But new research casts doubt on
this often-repeated advice. Adopting a low-fat diet rich in fruits, vegetables
and other sources of fiber does not prevent the development of intestinal
polyps in people who have already had polyps removed.
Polyps in your colon are growths on the lining of
the colon or rectum. Colon and rectal cancer is the second-leading cause
of cancer-related death in the United States, after lung cancer, and is
diagnosed in 130,000 Americans a year. Many people aged 50 and older develop
polyps, but only some of them become cancerous. Diet is thought to play
a role in the development of colon cancer, since the disease is much less
common in countries where people eat lots of fruits and vegetables and
fewer meats than in western countries.
Researchers studied more than 2,000 men and women
aged 35 and older who had already had at least one colorectal polyp removed.
Participants were randomly assigned to continue eating their regular diets
or to follow a diet containing 20% of calories from fat, 18 grams of dietary
fiber and 3.5 servings of fruits and vegetables per 1,000 calories.
About 4 years into the study, researchers did not
detect any significant difference in the development of colon polyps.
It's possible that dietary changes affect the process before the development
of polyps or a low-fat, high-fiber diet may affect the progression of
polyps into cancer, or the study may not have been long enough to detect
any effects of dietary changes.
A second study compared the effects of adding wheat-bran
to the diet. More than 1,400 men and women with a history of colon polyps
were randomly assigned to a low- or high-dose of wheat-bran each day.
After about 3 years, wheat-bran did not appear to make much of a difference.
About half of each group developed at least one polyp in their large intestine.
The New England Journal
of Medicine April 20, 2000;342:1149-1155,
1156-1162,
1206-1207.
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