Eating Soy During Adolescence May Reduce Breast Cancer

LOS ANGELES, Aug. 28 -- Eating soy foods on a regular basis-
especially during adolescence-might lower the risk of breast
cancer, according to preventive medicine researchers at the
Keck School of Medicine of USC and colleagues. Asian-
American women who consumed soy foods on a weekly basis
during their teen years and adulthood had about half the
risk of developing breast cancer compared to similar women
who ate little soy during the same time periods, according
to a study in the September issue of Carcinogenesis.

Risk also was somewhat lowered for women who ate soy
regularly during the teen years but consumed little during
adulthood. However, preliminary data suggest little added
benefit for women who ate little soy during adolescence but
a high amount of soy during adulthood.

"There has been a lot of talk and controversy about the
Asian diet and connections between soy food intake and
breast cancer. We wanted to look at soy very carefully, to
better understand if soy by itself is protective or if the
level of soy consumption is just a marker for
acculturation," says Anna H. Wu, Ph.D. professor of
preventive medicine at the Keck School of Medicine.

Wu and colleagues conducted a case-control study of breast
cancer among Chinese, Japanese and Filipino women in Los
Angeles County, specifically looking at the importance of
soy. From 1995 to 1998, they interviewed 501 Asian-American
breast cancer patients and compared them to 594 healthy
Asian-American women.

The researchers asked about eating habits, including how
many times each week during adolescence they ate tofu. They
also asked about the frequency and amounts of whole soy
foods, such as tofu, soymilk, miso and fresh soybeans,
usually eaten during adulthood.

Intake was highest among Chinese (26.8 milligrams of
isoflavones a day), intermediate among Japanese (18.4 mg of
isoflavones a day) and lowest among Filipinas (9.3 mg of
isoflavones a day). Migrants ate a little more soy than
American-born women did. Most of the Chinese and Filipino
women in this study-more than 90 percent-were born in Asia,
compared to less than 30 percent of the Japanese women.

When women were grouped by how often they ate soy during
adolescence and adult life, researchers found that women who
were high consumers during both time periods had a 47
percent reduction in risk. Those who ate little soy during
adult life but were regular soy consumers during adolescence
showed a 23 percent reduction in risk Women who were low
consumers during adolescence and high consumers during
adulthood showed little reduction in risk. However, the
number of such women was small, and researchers note that
larger studies must be conducted to confirm this result.

So how does soy work? Scientists are not sure, but they have
some ideas.

Animal studies indicate that early life exposure to
genistein-the main isoflavone in soybeans-seems to help
protect against chemically induced breast tumors. Getting
genistein early in life may help the mammary glands develop
in a favorable way.

Eating soy might also lead to lower levels of estrogen
circulating within the body, some theorize. And some studies
show that genistein seems to inhibit some enzymes that are
important in metabolizing estrogen.

Regardless of the protective mechanism, Wu notes that if the
mounting soy research shows promise, many may ask, "How much
soy is enough?" There may be a point at which eating more
soy does not further reduce risk, she says. Researchers are
still seeking to understand the relationship between soy
food dose and risk reduction, though in this study the
greatest risk reduction was seen among women with the
highest level of consumption: 12.68 mg or more of
isoflavones per 1000 kilocalories during adulthood and
eating soy foods four or more times a week during
adolescence.

Isoflavone levels in soy foods vary considerably, but a
serving of store-bought tofu-a quarter of a box-contains
about 10 mg of isoflavones, Wu says.

Wu notes that a much larger study is needed to sort out the
benefits of adult soy food intake and what levels of soy
intake are most helpful. Her study looked only at
traditional soy foods, not at genistein or other isoflavones
that may be contained in pills and supplements.

Reference: Anna H. Wu, Peggy Wan, Jean Hankin, Chiu-Chen
Tseng, Mimi C. Yu and Malcolm C. Pike, "Adolescent and adult
soy intake and risk of breast cancer in Asian-Americans,"
Carcinogenesis. September 2002, Vol. 23, No. 9, pp. 1491-
1496.

Do you know of a friend or family member with one or more of these milk-related problems? Do them a huge favor and forward the URL or this entire file to them.