Modernist-Cuisine-Vol.-1-Small

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For more on prospective studies, randomized
trials, meta-analysis, and other ways of
scientifically testing ideas about how what we
eat affects our health, see Testing a Dietary
System, page 218.
DIETARY SYSTEMS
The rise and fall of dietary fiber illuminates the
typical trajectory of a dietary system. You may
have heard that fiber-rich foods will help to reduce
your risk of colorectal cancer. This powerful idea
originated with Denis Burkitt, M.D., an Irish
medical missionary who spent many years in
Kenya and Uganda in the 1940s and thereafter.
Burkitt was a competent surgeon who is credited
with the discovery in African children of a new
type of cancer, now known as Burkitt’s lymphoma.
Burkitt also cast his keen eye upon colorectal
cancer, realizing that he had observed remarkably
few cases of it among the people he doctored.
Upon his return to the United Kingdom in the
1960s, he wrote up an anecdotal studya study
based solely on his own experiencecomparing
patterns of disease in British and African hospitals.
He concluded that there was less colorectal
cancer in Africa.
Whether this is actually statistically true is
unclear: Burkitt did not present a proper analysis.
Nevertheless, the idea that rural Africans had
lower rates of colorectal cancer was Burkitt’s
inspiration for a hypothesis. He speculated that
a diet high in fiber would push fecal matter out of
the gut more quickly so that residual bile acid
would have less time to have a carcinogenic effect.
This led to tireless promotion of the theory,
including a 1979 book for general audiences titled
Don’t Forget Fibre In Your Diet, which was an
international best seller and made him a nutrition
celebrity. While a few small studies seemed to
confirm Burkitt’s hypothesis, a few others seemed
to refute it. There certainly was no scientific proof
that fiber prevented colorectal cancer, however.
By 1984, food companies climbed on the
bandwagon. Kellogg added health claims to its
All-Bran brand of breakfast cereal. Changes in
U.S. federal law in 1990 allowed manufacturers
greater liberty to make health claims in food
advertisements and on labels. Health food stores,
cookbook authors, and journalists who covered
food and nutrition joined in. Soon, there were
hundreds of food products, books, and articles
proclaiming the benefits of high fiber content.
From a scientific perspective, however, the
connection between fiber and cancer was still little
more than speculation. Dietary studies are
notoriously rife with bias of various kinds and
plagued by confounding factors that can create an
illusion of a causal link where none really exists.
Durable conclusions can come only from large,
randomized intervention trials: studies that
randomly divide hundreds or thousands of people
into at least two groupsone of which eats
a specific diet and another that eats normally
and that then tracks the health of every subject.
Even then, chance can play a role, so results
cannot be considered definitive until several such
studies have arrived at the same conclusion and
have ruled out any possible confounders.
Did Burkitt’s idea have merit? The first tests
were performed using small, simple studies, which
are far quicker and much less expensive than large,
randomized trials. In some of these small-scale
studies, people who ate lots of fiber did seem to
experience lower rates of certain diseases. Burkitt
and others trumpeted these preliminary findings.
They should have been more cautious. Dietary
fiber comes from many kinds of food, and foods
are chemically complex things. Some contain lots
of potentially healthful compounds; fiber is just
oneor two, actually, because fiber comes in both
soluble and insoluble forms. So even if eating
certain foods with fiber does reduce disease,
a conscientious scientist has to ask whether the
effect is due to the fiber or to some other compound
that is along for the ride.
Twenty years after Burkitt published his book,
the first large, long-term trial on fiber reported its
results. The Nurses’ Health Study had followed
more than 88,000 women. After crunching the
numbers, the researchers concluded that no
matter how much fiber the nurses ate, their risk of
colorectal cancer was essentially the same.
Although this study was imperfect in many
ways, other prospective studies (in which people
have their health and lifestyles tracked over
a period of time) and randomized trials soon
reported the same results. High dietary-fiber
intake doesn’t significantly reduce the likelihood of
colon cancer, and a low-fat diet, a diet high in
fruits, or a diet high in vegetables doesn’t, either. In
fact, subjects in one study who ate more vegetables
actually showed a higher risk of colorectal cancer,
although the increase was so small that it was
likely just due to chance. None of the popular
dietary-system theories about colon cancer proved
to have any value.
Dodging Reality
Burkitt did not live to see his theory refuted. At
the time of his death in 1993, he was still being
feted for his great fiber discovery. One might think
that, confronted with such strong evidence that
there is no practical value in eating fiber to prevent
colon cancer, Burkitt’s followers and fellow fiber
advocates would recant. They did not. Instead, the
advocates switched gears as soon as the scientific
papers came out: they began arguing there were
plenty of other reasons to eat a high-fiber diet.
Sources that ostensibly should be even more
responsible acted likewise. When the U.S. National
Institutes of Health published the results of
the Polyp Prevention Trial and the Wheat Bran
Fiber Study in 2000, the press release included
a question-and-answer section. It gave three
answers to the question, “Why didn’t these trials
show a protective effect?” All three are excuses
seeking to explain away the results. None of them
concedes that the idea was wrong. Another part of
the press release tries to reassure people that there
are other reasons to eat a high-fiber diet.
This is intellectually dishonest, but it is also
human nature. People are reluctant to admit they
were wrong. This is particularly true for health
“experts” who want to maintain an aura of authority,
an aura that they know what is best. If they
admit the entire fiber escapade was a sham, people
might be less likely to believe them the next time
around.
Consumers might also be angry that they were
swindled into paying billions of dollars to buy
foods with useless fiber supplements that did
nothing to decrease their likelihood of contracting
colon cancer. Food companies have the most to
lose: they want to continue promoting their
high-fiber products and supplements, so they don’t
want to admit that the whole fiber issue was based
on what was, at best, a mistake.
To this day, you’ll hear statements from nutrition
authorities, particularly in the mainstream
press, that tout the cancer-preventing benefits of
high-fiber diets. A 2008 position paper from the
American Dietetic Association states, “Despite the
inconsistency in the results of fiber and colon
cancer studies, the scientific consensus is that there
is enough evidence on the protectiveness of dietary
fiber against colon cancer that health professionals
should be promoting increased consumption of
dietary fiber.” Yet nothing of the sort is true. The
data from clinical trials consistently and conclusively
fail to show any benefit from fiber for colon
cancer. Such a stubborn grip on dogma is irresponsible
but typical of converts to dietary systems.
Health claims dominate the packaging of many kinds of foods these days. But these promises are rarely based on
sound science, and government authorities do little to keep manufacturers from stretching the truth.
214 VOLUME 1 · HISTORY AND FUNDAMENTALS
FOOD AND HEALTH 215