Past studies have come to differing conclusions on a
possible association between dietary fat and breast cancer. Whether
the two are even linked at all remains controversial.
The new report, a second analysis of a large, long-term study,
suggests that fat may play a role in the development of certain
forms of the disease but not others, the authors said.
Still, it cannot prove that a high-fat diet is the reason any of the
women got cancer.
"In our study we confirm that saturated fat intake was positively
associated with breast cancer risk," lead author Sabina Sieri, from
the Fondazione IRCCS National Cancer Institute in Milan, Italy, told
Reuters Health in an email.
"Saturated fatty acids intake should be as low as possible within
the context of a nutritionally adequate diet."
Saturated fat in the diet most often comes from meat and other
animal products like butter and cheese.
The research team's findings are based on a study of about 337,000
women from 10 European countries. They filled out questionnaires
about their diet and lifestyle and were followed for an average of
11 to 12 years.
During that time, about 10,000 of the women were diagnosed with
The original study found that women who ate the most saturated fat
were more likely to develop breast cancer than those who ate the
For the new analysis, the researchers used patient medical records
to classify breast cancers into specific subtypes, for instance
based on whether the tumor may respond to the hormones estrogen and
They found that women with diets high in saturated fat were 28
percent more likely to develop tumors that had receptors for
estrogen and progesterone than women with the lowest saturated fat
in their diets. The pattern was similar for total fat intake.
However, the chance of developing breast tumors without receptors
for those hormones was not linked to dietary fat, according to the
findings published in the Journal of the National Cancer Institute.
The researchers said it's possible dietary fat increases the level
of sex hormones in the body. That could explain why high-fat diets
are tied to a greater risk of tumors whose growth is related to
estrogen and progesterone, known as hormone-receptor-positive
cancers. Those cancers make up the majority of breast cancer
Sieri and colleagues found that high levels of saturated fat were
also linked to a greater risk of HER2 negative breast cancer, but
not HER2 positive disease. HER2 stands for human epidermal growth
factor receptor 2 and is one factor used to determine how fast a
cancer is growing.
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Dr. Clifford A. Hudis, chief of Memorial Sloan Kettering Cancer
Center's Breast Cancer Medicine Service in New York, said the extra
risk of hormone-receptor-positive cancer linked to saturated fat was
What's more, he added, "These patients were not randomly assigned
to follow one diet or another."
That means other differences between women who ate high- and low-fat
diets may have factored into their cancer risk.
Still, Hudis said, the findings are consistent with recent research
looking at specific types of breast cancer and make sense based on
what is known about the biological effects of dietary fat.
Dr. Michelle Holmes, who has studied diet and breast cancer at
Harvard Medical School and the Harvard School of Public Health in
Boston, said that in the grand scheme of things, any possible link
between fat and breast cancer still seems to be small.
"In my opinion, the bottom line is that if the association with
fat and breast cancer exists, it's fairly small (and) it's probably
limited to certain subtypes," Holmes told Reuters Health.
Even though the new study included a "huge" number of women, she
said, "the answer doesn't leap out at you."
Hudis and Holmes, who were not involved in the new research, agreed
there's no reason women shouldn't still cut back on saturated fat.
"Saturated fat is bad for heart disease anyway," Holmes said.
"The associations with dietary fat are much stronger for heart
disease, which still kills more women than breast cancer in the
Journal of the National Cancer Institute, online April 9, 2014.
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