| Colon
Cancer |
| Bashing
the Bran Hypothesis |
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By
Miriam Komaromy,
MD
Reviewed
by Peggy Conrad,
MS, CGC
Last
updated November 8, 2000
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Dietary
fiber may not reduce your risk of colon cancer. Two
large experimental studies that spaned four years and
were published in April, 2000 cast a shadow of doubt
over the conventional wisdom that fiber reduces the
risk of colon cancer.
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What
the New Studies Discovered About Fiber
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Both
studies concluded that increased dietary fiber does
not:
- Decrease
the number of polyps
- Decrease
the size of polyps
- Decrease
the number of colon cancers
Yet,
most studies of populations with high fiber diets have
shown lower rates of colon cancer. Why?
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 top |
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| Possible
Explainations |
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There
are a number of possible explainations for the results
of these studies:
- Lifestyle.
It may be that the low rates of colon cancer in these
populations are due to some other dietary or lifestyle
factor.
- Study
design. It is possible that fiber really does
reduce colon cancer risk, but experimental studies
have been unable to prove it. For example, the factors
that cause or prevent polyps or colon cancer could
have their effect many years before polyps or colon
cancer develop. If this were the case, a four-year
trial wouldn't be long enough to show a beneficial
effect of fiber on the development of polyps or colon
cancer.
- Fiber
type. The
decrease in colon cancer may not due to fiber in general,
but to one particular type of high-fiber food.
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| Does
Fiber Increase the Risk of Colon Cancer? |
| A
study published in October 2000 raises the possibility
that not only does fiber not decrease the risk
of colon cancer, it may actually increase the risk.
In this study, patients with a previous colon polyp were
somewhat more likely to develop a second polyp if they
received a fiber supplement than if they did not. Does
this mean that fiber increases the risk of colon cancer?
We still don't know the answer to this question. In this
study the effect of fiber on developing colon polyps was
only weakly significant, meaning it could have occurred
by chance. Also, the fiber supplement was just one type
of fiber, and is not found in a normal diet. Finally,
this was only a single, fairly small study; more and larger
studies with different types of fiber and similar findings
would be needed before we can conclude that fiber causes
colon cancer.
For
recent news about whether fiber increases colon cancer
risk, see Related News below.
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| Should
You Eat Less Fiber? |
| A
diet high in fruits, vegetables, and grains still appears
to promote good health in a number of ways. However, it
will be important to follow new information on colon cancer
and diet to find out if dietary changes will be prudent
in the future for patients at increased risk of developing
colon cancer.
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| Colon
Cancer Prevention |
|
Screening for and removing polyps with colonoscopy
and sigmoidoscopy
remain the best methods for preventing colon cancer. |
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 |
 More
fiber may not mean fewer colon cancers |
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| References
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Alberts,
D. et al. (2000). Lack of effect of high-fiber cereal
supplement on the recurrence of colorectal adenomas.
N Engl J Med 342(16): 1156-62.
Schatzkin,
A. et al. (2000). Lack of effect of a low-fat, high-fiber
diet on the recurrence of colorectal adenomas. N
Engl J Med 342(16): 1149-55.
Byers,
T. (2000). Diet, colorectal adenomas, and colorectal
cancer. N Engl J Med 342(16): 1206-7.
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