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general interest
article
The fiber-colon connection - media
keeps getting it wrong
by Jeff D Leach
Paleobiotics Lab
Newspapers and
health websites throughout the world plugged the story much the same,
“Dietary Fiber Not Protective Against Colon Cancer” and the predictable
follow-up, on “No Need To Eat Fiber Anymore.” The CNN website pretty much
sums up the common theme among news reports with their own pronouncement
“Harvard researchers burst a lot of bubbles by reporting that dietary
fiber doesn't reduce the risk of colorectal cancer.”
The problem is –
they all kinda got it wrong.
In the rush to
get out the “no need to rough it with roughage” story following the
publication of a report on dietary fiber intake and risk of
colorectal cancer by Harvard researchers in the
Journal of the American Medical Association, reporters forgot to read
the report – at least carefully.
In their study,
Harvard researchers pooled the data from 13 separate studies that followed
725,628 men and women over a 6 to 20 year period to access the role of
dietary fiber intake against the likelihood of developing colon cancer.
One of the conclusions reached by the study, and the one parroted by news
reporters around the world, “high dietary fiber intake was not associated
with a reduced risk of colorectal cancer.”
However, a little
closer read of the results and review of the accompanying
editorial published in the same issue, indicate a little different
headline may be in order for any reporter willing to take the time.
According to the US Food Pyramid, a daily intake of 20 to 38 grams a day
of fiber is recommended, depending on age, gender, and activity level. For
most adults, this means somewhere north of 30 grams a day is recommended.
In the Harvard
study, the difference in fiber intake among the pooled data from the
lowest to highest was 14 to 28 grams for men and 13 to 24 grams for women.
This means the average participant was eating far less than the
recommended daily amount of fiber.
According
to an editorial published in the same issue, John Baron, Professor of
Medicine and of Community & Family Medicine at Dartmouth Medical School,
made the following observation after reviewing the complicated analysis
and statistics presented in Harvard report:
“Park
[lead Harvard researcher] found evidence of an increased risk of
colorectal cancer among individuals with very low intake of
total dietary fiber…After adjustment for measurement error, the
relative risk for intakes of less than 10 g per day versus 10
or more g per day increased from 1.22 to 2.16.”
Translation:
people with the lowest fiber intake were at nearly twice the risk for
colon cancer than those with the higher fiber intake. This critical
information was missed in the numerous reports appearing in newspapers and
websites read by millions of consumers eager to improve overall health and
well-being.
This same
editorial went on to say “the European Prospective
Investigation into Cancer and Nutrition (EPIC) investigators
found a more than 40% reduction in risk of colorectal cancer
for individuals in the highest quintile of dietary fiber intake
vs the lowest…The findings by Park [lead Harvard researcher] and the
results of the EPIC analysis provide at least some indications
that dietary fiber of some sort is related in some way to colon
or rectal cancer risk.”
The
EPIC study referenced in the editorial was a prospective study of over
half a million participants between the ages of 27 and 70 from ten
European countries that found that fiber played a protective role in risk
to colorectal cancer. The Harvard analysis did not consider the EPIC study
in its analysis.
As the Harvard
study suggests, the black and white role of fiber in risk of developing
colon cancer is not as clear cut as most would like. The data and
subsequent sophisticated analysis are further complicated by the fact the
in all of the studies pooled in the Harvard analysis, daily intake of
fiber was generally low across the board – and even lower from an
evolutionary perspective that reveals our ancestors ate much greater
amounts of fiber (75 to 150 grams a day) – and that all of the pooled
study participants were consuming western diets.
Western diets,
which are notoriously high in saturated fat, cholesterol, and red meat,
are considered risk factors in the development of colon cancer. In other
words, they may be mudding the analytical waters.
The role of the
“low across the board” fiber intake noted in the Harvard analysis and the
complicating factors of western dietary habits is well-illustrated in a
global analysis of the incidence of colorectal cancer. For example, in the
1960s men living on a high fiber (non western) diet – with fiber intakes
closer to our evolutionary intake of 100 grams or more a day – had an
incidence of colorectal cancer of 3.5 per 100,000 in Uganda and 5.3 per
100,000 in Mozambique. Compare this to low fiber, westernized diets in
Scotland and the United States that produced an incidence of colorectal
cancer of 51.5 per 100,000 and 51.8 per 100,000, respectively.
This means a
nearly ten fold increase in your incidence of colorectal cancer based on a
low versus high intake of fiber and whether or not you consumed a
westernized diet.
In future
studies, it would be useful for researchers to consider an evolutionary
perspective on fiber intake while trying to split statistical hairs with
populations that are clearly eating extremely low amounts of fiber in the
first place.
As long as
researchers, reporters, and the general public consider current US Food
Pyramid guidelines on fiber intake as adequate or high, and continue to
compare and derive results only from populations eating a
highly-processed, high fat and added sugar, and high red meat diets,
meaningful conclusions on the important role of dietary fiber in human
health may not be forthcoming.
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