284 THE CHINA STUDYfiber or fruits and vegetables does not kick in against colorectal cancer
until there is a complete dietary shift away from an animal-based diet.
Between the colon cancer and breast cancer findings, the Nurses'
Health Study has done much to confuse, if not discredit, the idea that
diet is related to cancer. After these decades of work, Professor Walt
Willett says:... increasing fruits and vegetables overall appears to be less prom-
ising as a way to substantially reduce cancer risk. ... the benefits
[of these foods] appear greater for cardiovascular disease than for
cancer^4This statement sounds a bit ominous. Colon cancer, historically one
of the first cancers said to be prevented by a plant-based diet,43-45 now is
being said to be unrelated to diet? And low-fat diets don't prevent breast
cancer? With results like these, it's only a matter of time before the hy-
pothesis of a dietary connection to cancer starts falling apart. In fact, I
have already heard people within the scientific community beginning to
say that diet may have no effect on cancer.
These are the reasons that I believe that the Nurses' Health Study has
done considerable damage to the nutrition landscape. It has virtually
nullified many of the advances that have been made over the past fifty
years without actually posing a scientifically reliable challenge to earlier
findings regarding diet and cancer.
This problem of studying a population that uniformly consumes a
high-risk diet and looking at the differences in consumption of one nu-
trient at a time is not unique to the Nurses' Health Study. It is common
to virtually all studies using Western subjects. Furthermore, there is
little or no value to pooling the results of many large studies for analysis
in order to get a more reliable result if all the studies have the same flaw.
A pooling strategy is often used for identifying cause-and-effect associa-
tions that are more subtle and uncertain within single studies. This is a
reliable assumption when each study is properly done, but obviously it
is not when all the studies are similarly flawed. The combined results
only give a more reliable picture of the flaw.
The Harvard researchers have done several of these multi-study
pooled analyses. One such pooled analysis concerned the question of
whether meat and dairy foods had any effect on breast cancer.26 A previ-
ous 1993 pooling of nineteen studies^46 had shown a modest, statistically
significant 18% increase in breast cancer risk with increased meat intake