More Fiber May Not Mean Fewer Colon Cancers
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WESTPORT, CT (Reuters Health) Oct 13 - Fiber supplementation may
increase
the risk of colorectal adenoma recurrence, whereas calcium
supplementation
may reduce the risk of recurrence of these lesions, according to a
report in
the October 14th issue of The Lancet.

Epidemiologic studies of the value of dietary fiber, vegetables,
whole-grain
cereals, and calcium in preventing colorectal adenomas and cancer have
yielded inconsistent results, the authors explain. Animal studies,
though,
suggest potent antitumor activity of such soluble, mucilaginous fibers
as
ispaghula husk.

Accordingly, Dr. Claire Bonithon-Kopp, from Faculte de Medecine de
Dijon,
France, and colleagues evaluated the effects of calcium, fiber
(ispaghula
husk), or no changes in diet on 552 patients with a history of
colorectal
adenoma.

A greater proportion of fiber-treated patients (29.3%) than control
group
patients (20.2%) developed at least one adenoma during the 3-year
study,
representing a 63% increase in risk, the authors report. The risk was
even
higher (nearly a two-fold increase) among fiber-treated patients who
had a
higher than median dietary calcium consumption.

In contrast, patients who took calcium supplements were only about 75%
as
likely to develop recurrent adenomas as the control group patients
were, the
report indicates, though the difference failed to reach statistical
significance.

Neither treatment compliance nor any of a number of demographic
variables
altered the relative risks faced by the three treatment groups, the
researchers note.

These findings, along with those from two American trials, suggest
that
"low-fat, high-fiber diet and supplementation with wheat-bran fiber or
ispaghula husk may not be effective strategies for the prevention of
colorectal adenoma recurrence," the authors conclude.

Noting the complexity of dietary interventions, they add that these
results
"should not prevent recommendations for high consumption of
vegetables,
fruits, and cereals, because this approach has potentially beneficial
effects on other chronic disease, especially coronary heart disease."

Dr. Bonithon-Kopp told Reuters Health that these results do not signal
a
need to change recommendations about prudent diets. "The increase in
risk of
adenoma recurrence was found after a supplementation with a soluble
fibre
which is not found in usual diet," she emphasized. "Furthermore, this
deleterious effect was observed only on the early stages of the
adenoma-cancer sequence. We don't know if such an effect would be
observed
on later stages [such as] on malignant transformation. Thus, usual
recommendations regarding dietary fibre intake remain valid."

Dr. Bernard Levin, from the University of Texas M. D. Anderson Cancer
Center, in Houston agrees with the conclusions in a related
commentary. "The
search for more effective targeted inhibitors of colorectal adenomas
continues," he writes. "This goal may be realized by novel approaches
using
nonsteroidal anti-inflammatory agents alone or in combination."

Lancet 2000;356:1300-1306,1286-1287.