88 THE CHINA STUDY
fat consumption is associated with higher blood levels of estrogen dur-
ing the critical years of thirty-five to forty-four yearsIll and higher blood
levels of the female hormone prolactin during the later years of fifty-five
to sixty-four years.Ill These hormones are highly correlated with animal
protein intakeIll and milkIll and meatY Unfortunately, we could not dem-
onstrate whether these hormone levels were directly related to breast
cancer risk in China because the rate of disease is so low.^3?
Nonetheless, when hormone levels among Chinese women were com-
pared with those of British women,38 Chinese estrogen levels were only
about one-half those of the British women, who have an eqUivalent hor-
mone profile to that of American women. Because the length of the repro-
ductive life of a Chinese woman is only about 75% of that of the British
(or American) woman, this means that with lower estrogen levels, the
Chinese woman only experiences about 35-40% of the lifetime estrogen
exposure of British (and American) women. This corresponds to Chinese
breast cancer rates that are only one-fifth of those of Western women.
The strong association of a high-animal protein, high-fat diet with
reproductive hormones and early age of menarche, both of which raise
the risk of breast cancer, is an important observation. It makes clear that
we should not have our children consume diets high in animal-based
foods. If you are a woman, would you ever have imagined that eating
diets higher in animal-based foods would expand your reproductive life
by about nine to ten years? As an aside, an interesting implication of
this observation, as noted by Ms. magazine founder Gloria Steinem, is
that eating the right foods could reduce teenage pregnancy by delaying
the age of menarche.
Beyond the hormone findings, is there a way to show that animal-
based food intake relates to overall cancer rates? This is somewhat dif-
ficult, but one of the factors we measured was how much cancer there
was in each family. Animal protein intake was convincingly associated
in the China Study with the prevalence of cancer in families. III This as-
sociation is an impressive and significant observation, considering the
unusually low intake of animal protein.
Diet and disease factors such as animal protein consumption or
breast cancer incidence lead to changes in the concentrations of cer-
tain chemicals in our blood. These chemicals are called biomarkers.
As an example, blood cholesterol is a biomarker for heart disease. We
measured six blood biomarkers that are associated with animal protein
intake.^39 Do they confirm the finding that animal protein intake is asso-