The China Study by Thomas Campbell

52 THE CHINA STUDY

At the time we started our research, we hypothesized that the protein
we consume alters tumor growth by changing how aflatoxin is detoxi-
fied by the enzymes present in the liver.
We initially determined whether the amount of protein that we eat
could change this enzyme activity. After a series of experiments (Chart
3.2^18 ), the answer was clear. Enzyme activity could be easily modified
simply by changing the level of protein intake.^1 s-^21
Decreasing protein intake like that done in the original research in
India (20% to 5%) not only greatly decreased enzyme activity, but did
so very qUickly. 22 What does this mean? Decreasing enzyme activity via
low-protein diets implied that less aflatoxin was being transformed into
the dangerous aflatoxin metabolite that had the potential to bind and to
mutate the DNA.
We decided to test this implication: did a low-protein diet actually
decrease the binding of aflatoxin product to DNA, resulting in fewer
adducts? An undergraduate student in my lab, Rachel Preston, did the
experiment (Chart 3.3) and showed that the lower the protein intake,
the lower the amount of aflatoxin-DNA adducts.^23
We now had impressive evidence that low protein intake could mark-
edly decrease enzyme activity and prevent dangerous carcinogen bind-
ing to DNA. These were very impressive findings, to be sure. It might
even be enough information to "explain" how consuming less protein
leads to less cancer. But we wanted to know more and be doubly assured
of this effect, so we continued to look for other explanations. As time
passed, we were to learn something really quite remarkable. Almost ev-

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CHART 3.2: EFFECT OF DIETARY PROTEIN ON ENZYME ACTIVITY

250

200

150

100

50

0

20% Protein

76% decrease

in enzyme

activity with

low-protein

diets

5% Protein