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University of California, Los Angeles.
The human evidence that dietary fiber prevents
the development of colon cancer has been
reviewed. The correlational studies are
consistent with a protective effect in
61.9 per cent of reports. However, these
studies are all retrospective and largely
uncontrolled. The case-control studies
provide evidence of a protective effect
in only 48 per cent of reports.
It is of
additional concern that some human studies
have found an association between tumor
enhancement and some fiber-containing foods.
Whereas this is not sufficient evidence
to implicate dietary fiber as a promoter
of human colon cancer, it does perhaps
argue for a more conservative approach
to recommending high-fiber diets as a means
of cancer prevention. The animal data show
that different sources of dietary fiber
produce markedly different effects on colon
carcinogenesis.
Although some fibers exhibit
protective properties, others clearly promote
tumor development. The mechanisms behind
these opposing actions require further
investigation. However, one thing is clear
and that is that dietary fibers do modulate
the carcinogenic process and as such provide
a valuable tool for probing the mechanisms
and stages of colon tumor development.
Dietary
fiber appears to play a major role in the
regulation of normal intestinal function
and in the maintenance of a healthy intestinal
mucosa. Although there is some evidence that
a fiber-deficient diet predisposes to colon
carcinogenesis, it is still not known whether
an increase in fiber consumption will prevent
the development of colon cancer.
This is
further complicated by not knowing what constitutes
a normal level of fiber intake. In the interim,
physicians should perhaps advise their patients
to consume a moderate diet that contains
vegetables, fruits, and whole grains. This
will provide a varied source of fiber-containing
foods and if consumed in sufficient quantity
will optimize intestinal transit and bulk
according to individual needs. Isolated
fiber supplements have not been shown to
be effective in colon cancer prevention.
Further
attempts to be more specific about what type
of fiber to recommend seem premature at this
time. However, an intake in the range of
20 to 35 gm per day of dietary fiber from
foods has recently been recommended by an
Expert Panel.
PMID: 2852641 [PubMed
- indexed for MEDLINE
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