56 THE (HINA STUDYstill have an effect? We investigated this question by giving two groups
of rats either a high-aflatoxin dose or a low-aflatoxin dose, along with a
standard baseline diet. Because of this the two groups of rats were starting
the cancer process with different amounts of initiated, cancerous "seeds."
Then, during the promotion phase, we fed a low-protein diet to the high-
aflatoxin dose groups and a high-protein diet to the low-aflatoxin dose
group. We wondered whether the animals that start with lots of cancerous
seeds are able to overcome their predicament by eating a low-protein diet.
Again, the results were remarkable (Chart 3.5). Animals starting with
the most cancer initiation (high-aflatoxin dose) developed substantially
less foci when fed the 5% protein diet. In contrast, animals initiated with
a low-aflatoxin dose actually produced substantially more foci when sub-
sequently fed the 20% protein diet.
A principle was being established. Foci development, initially deter-
mined by the amount of the carcinogen exposure, is actually controlled
far more by dietary protein consumed during promotion. Protein dur-
ing promotion trumps the carcinogen, regardless of initial exposure.
With this background information we deSigned a much more sub-
stantial experiment. Here is a step-by-step sequence of experiments,
carried out by my graduate student Linda Youngman. 35 All animals were
dosed with the same amount of carcinogen, then alternately fed either
5% or 20% dietary protein during the twelve-week promotion stage.
We divided this twelve-week promotion stage into four periods of three
weeks each. Period 1 represents weeks one to three, period 2 represents
weeks four to six, and so on.
When animals were fed the 20% protein diet during periods 1 and 2
(20-20), foci continued to enlarge, as expected. But when animals were
switched to the low-protein diet at the beginning of period 3 (20-20-
5), there was a sharp decrease in foci development. And, when animals
were subsequently switched back to the 20% protein diet during period
4 (20-20-5-20), foci development was turned on once again.
In another experiment, in animals fed 20% dietary protein during
period 1 but switched to 5% dietary protein during period 2 (20-5), foci
development was sharply decreased. But when these animals were re-
turned to 20% dietary protein during period 3 (20-5-20), we again saw
the dramatic power of dietary protein to promote foci development.
These several experiments, taken together, were quite profound. Foci
growth could be reversed, up and down, by switching the amount of
protein being consumed, and at all stages of foci development.