Eating fiber-rich vegetables, fruit and whole grain foods
may reduce risk of breast cancer in pre-menopausal women, but not in
postmenopausal women, according to a new
UK study, which found that those
who ate highest amounts to total dietary fiber cut their risk of breast cancer
by 50 percent.
Fiber from whole grain products such as cereals was
inversely associated with reduced risk of breast cancer.
While fiber in other foods was associated
with a reduced risk of breast, but the association was not statistically
Earlier studies are inconsistent with regard to the effect
of dietary fiber on risk of breast cancer. The inconsistency may be due to the
fact that the range of fiber intake was too narrow in the study subjects,
according to researchers of the current study.
In the current study, Janet Elizabeth Cade at
Leeds and colleagues followed 35,792
women including 17,781 postmenopausal women and 15,951 pre-menopausal women aged
45 and 59 on average respectively, who entered the UK Women's Cohort Study
(UKWCS) between 1995 and 1998.
A food frequency questionnaire (FFQ) was collected as the
baseline data at the start of the study. The second FFQ was taken from a sample
of 1918 or 5 percent of the cohort. Fiber and other nutrients were calculated
and cancer cases were checked out from cancer registries.
During the 6.7-year study, 350 post-menopausal women and 257
pre-menopausal women were diagnosed with invasive breast cancer.
The non-breast cancer subjects were followed
for 7.5 years on average.
The participants with 99 percent white women had a mean body
mass index 24.5 kg/m2.
18 percent of the
women were vegetarian, 12 percent fish-eaters and 70 percent meat eaters.
The mean energy intake was 2360 kcal with 32 percent from
fat, 53 percent from carbohydrates, and 15 percent from protein.
The mean fiber intake was 26 g/day with 29 g/day found in
fish eaters, 28g/day in vegetarians and 24 g/day in meat eaters.
"Pre-menopausal women with breast cancer had a higher
percentage of energy derived from protein and also lower total carbohydrate,
sugar, dietary fibre (Englyst) and vitamin C compared with cancer-free
women," the researchers write in their report. "Only the difference
in percentage energy from protein was statistically significant in this
Those pre-menopausal women whose intake of total dietary
fiber was in the highest quintile (30 grams or more per day) were 50 percent
less likely to have breast cancer compared to those whose intake of total fiber
was in the lowest quintile (20 grams or less per day), the researchers found.
When other factors such as folate were considered as
confounders, the inverse association between total dietary fiber and breast
cancer risk in the pre-menopausal women became even stronger.
That is, those who consumed the highest total
fiber were 67 percent less likely to develop breast cancer compared to those
who ate the lowest quintile of total fiber.
According to the researchers, a few mechanisms have been
proposed earlier to explain the protective effect of dietary fiber on the risk
of breast cancer. Fiber may inhibit reabsorption of estrogen and androgens and activity
of human estrogen synthetase, which in turn reduces production of
Both estrogen and androgens
have been linked to higher risk of breast cancer.
Other researchers say that fiber may also reduce absorption
of toxic chemicals, which may be another mechanism by which dietary fiber
reduces the breast cancer risk.
An interesting observation the researchers did not elaborate
is that compared to the pre-menopausal women without cancer, the pre-menopausal
cancer patients ate higher amounts of protein, which may be a potential risk,
according to a scientist affiliated with foodconsumer.org.
Early studies have at least indirectly linked high consumption
of meat (high fat/high protein) with high cancer risk, according to Dr. T.
Colin Campbell, a prominent nutrition professor from
Early studies have found dietary IGF can influence the serum
levels of IGF-1 in humans, which has been linked with increased risk of breast
cancer, according to the researchers of the current study, who did not
elaborate the effect of meat on the breast cancer risk.
The current study did not find an association between
dietary fiber and breast cancer risk in post-menopausal women.
“In post-menopausal women, nutrient intakes
did not differ greatly between those with and without breast cancer,”
the researchers write. This observation was in consistency with previous
studies, according to the researchers.
The researchers explain that "the estrogen metabolism
pathway differs between pre-and post-menopausal women."
In one early study, women supplemented with 10 or 20 grams
of fiber-rich wheat bran each day for 2 months had significantly lower
ostradiol concentrations. The study was published in 1997 by Rose DP, Lubin M, and
Connolly J.M. in Nutrition 13:535–39.
Another study, published in 1998 by Stark AH, Switzer BR, and
Atwood JR, et al. in Nutr Cancer 31:138–42 found that in postmenopausal women,
wheat bran supplementation did not reduce estradiol, androstenedione or sex
In yet another study, reported in 1999 by Barr S. I. in American
Journal of Clinical Nutrition, 70:549s–54s, a high fiber diet or vegetarian
diet was found to affect cycle length in pre-menopausal women, which is linked
to estrogen exposure, but this effect was not found among postmenopausal women.
The intake of dietary fiber in an average American is 10 to
12 grams per day.
The study suggests
that to have a protective effect against breast cancer, a woman needs to eat 30
grams or more per day.
U.S., 178,480 women will be
diagnosed with invasive breast cancer this year and 40,910 are expected to die
of the disease, according to the latest report released by the American Cancer
Janet Elizabeth Cade, Victoria Jane Burley, Darren Charles
Greenwood, and the
Women's Cohort Study Steering Group
Dietary fibre and risk of breast cancer in the UK Women's
IJE Advance Access published on January 24, 2007.