The wheat-bran study asked subjects to change
their eating habits to include a breakfast cereal or snack bar that
would give an extra 2 grams (control group) or 13.5 grams (treatment
group) of fiber per day. But there were a few problems. First, only
about one-third of the subjects completed the study. Then, while
researchers aimed for an 11.5 gram difference in fiber intake, a
dietary analysis of the subjects near the end of the study showed
that the difference was only 9.4 grams -- only about a 50% increase
over their starting level of 19 grams per day. Dietary fiber intake
in developing countries where colon cancer is low is often 30-50
grams per day. Next, the dietary changes required them to eat a
breakfast cereal, presumably with milk, and to eat snack food. In
general these would not really be considered an entirely healthy
habits. This was not so much a dietary supplement as a dietary addition
One problem with this kind of study is that diets
are not like medicines. In a study of a new medicine, the control
group would take no medicine. However, in dietary studies can we
ask the control group to eat no diet? People will always eat something
and giving them something new to eat means that other compensating
changes get made in the diet. This makes interpretation of dietary
This was also an older group with an average
age of 66. This means that many subjects in the study probably started
eating their current diet when Herbert Hoover was in the White House.
Will just four years of a sugary fibrous cereal really make an impact
on this lifetime dietary pattern? Compare this to a typical man
in China who has been eating rice and vegetables for as many years
and does not spend a minute of his waking time worrying about colon
cancer. This wheat-bran dietary treatment was probably "too little
Cultural Bias and the Western Low-Fat,
The second study was much more difficult and
potentially more rewarding. But the results were the same: no dietary
effect on recurring polyps. Getting people to change their diets
is difficult. To their credit these researcher got their subjects
to dramatically change their diet to a healthier low-fat high-fiber
diet. They saw a 10% drop in fat intake to an astonishingly low
level -- for Americans -- of 24% of calories. Fiber intake went
up about 70% to 35 grams per day. Fruit and vegetable intake increased
about 2 servings per day and the subjects lost 2 1/2 pounds of weight
over 4 years compared to the control group.
The problems they had with their study are the typical problems
of doing dietary research in the US. The diet-colon cancer connection
was first suggested in studies observing African populations, where
colon cancer rates are very low. It was also based on numerous other
observational studies showing that when individuals in these low-risk
populations adopt a Western diet, they assume the same far higher
risk of colon and other cancers found in Western countries. Thus
it would seem to make sense to test the dietary habits of these
low-risk populations against the common high-risk dietary pattern
in the US to determine how the non-Western diets are protective.
However, this study did not, and probably could not, attempt this.
While the researchers, familiar with the international
studies, may have wanted to get their subjects to adopt a dietary
pattern that looked like rural Africa or China, they knew that this
was impossible given the subjects they had to work with. They chose
only to test what actually amounted to modest changes compared to
the non-Western low-risk diets, since if they put these older American
subjects on the vegetarian or near-vegan diets found to be protective
in Asia and Africa, the subjects might drop out of the study.
The relatively modest change in diet habits of
the study participants explains why their cholesterol levels had
almost no change. They were still eating their meats. On average
the treatment group subjects were eating one less mouthful of meat
(15 grams) per day compared to controls and dairy intakes were not
even reported. Their serum carotenoid levels were not increased
much, indicating that they were not eating many additional orange,
yellow, or green vegetables and fruits.
More Questions than Answers
The authors themselves gave several reasons why
they did not get the results they were hoping for. The study examined
the recurrence of intestinal adenomas. While everyone agrees that
some of these growths may eventually turn cancerous, this is only one
part of a long process of getting and dying from cancer. Maybe fiber
and low fat have their primary effects on some other, probably earlier,
stage of carcinogenesis. For example, higher fiber and lower fat
have been shown to decrease the transport of mutagens to the colon
cells, a very early step in the cancer process. Other biochemical
studies support this view.
Furthermore, the treatment group knew that they
were supposed to be eating a low-fat high-fiber diet. Therefore
when the researchers came around to ask them what they were actually
eating, they probably tended to err in their reporting on the healthy
side. Therefore the published fiber intakes may have been overestimates
of actual intake.
Were the changes the researchers were asking
for from their subjects enough to see an effect? Probably not. Could
they have asked their subjects to make even bigger changes? Probably
Did the researchers choose the right nutrients
and foods to modify? Numerous medical studies indicate that low
meat consumption reduces risk of colon cancer. If the researchers
had focused on reducing meat, dairy, and eggs rather than increasing
fiber, they might have seen a reduction in polyps.
It is possible that preventing colon cancer with
fiber and low fat should be done in the teenage years -- when these
study participants (average age of 61) were busy dancing in bobby
socks. Many of these folks were also overweight, with an average
BMI of 27. This is another problem of doing research in a country
where the average adult is often more than 20 pounds overweight.
Being overweight in itself is a known risk factor for colon cancer.
Thinking Outside the Box
There is a possible analogy between these studies
and a study completed a few years ago in Finland. Smokers were randomized
to receive, or not receive, a dietary supplement of beta-carotene
that was widely believed to prevent lung cancer. Not only did the
beta-carotene not have an effect -- but it appeared to actually
increase the rate of lung cancer in these smokers. While the researchers
suggested several reasons why the beta-carotene did not work, one
explanation that was widely accepted is that smokers are so "predestined"
to have lung cancer that a simple pill given very late in the process
is just overwhelmed by the cancer. What we are seeing with fiber
and colon cancer may be the same situation -- the cancer process
is too far advanced to be stopped by modest dietary changes.
Do we wish that the results of these studies
were different? Yes. Much previous research supports the hypotheses
they were testing and we, as a nation, need to really get serious
about this disease. Are we surprised at these negative results?
Not really, after a careful reading of the reports. The diets, which
appear protective in Asia and Africa and in studies of low-risk
groups in the US -- are shown to be vegetarian or near-vegan diets.
These are the diets that should be studied further, now that it
seems clearer that a modest modification in the Western diet is
not protective. Merely adding some fiber and lowering some fat --
while continuing to consume large amounts of meat and dairy -- does
not appear protective against colon cancer, according to these studies.
Researchers must begin to think outside the box,
and get beyond their own (and our own) cultural and traditional
dietary biases. After all, individuals at high risk of colon cancer
might happily adopt a no-meat and no-dairy diet if large, well-funded
studies like these confirmed the protective quality of a vegan diet.
But where and how to do these studies remains a problem.
I invoke the mantra of all researchers; "More
research is needed."
Comments? Please post them on the New
Century Nutrition Discussion board.
Marty Root has a PhD in Nutrition from Cornell
University, and works as a Senior Research Scientist at BioSignia,
Inc. in Chapel Hill, NC. His work involves making statistical
models that predict the onset of chronic diseases such as heart
disease and the cancers. He also writes for New
Century Nutrition. Dr Root is married and has three children.