Women whose diets included a lot of fat — particularly, a large amount of saturated fat from animal products — were more likely to develop certain types of breast cancer, compared with women who consumed less fat, the research found. The study included data from 337,000 women ages 20 to 70 in 10 countries in Europe; the women were followed for an average of 11.5 years.
“This study indicates that a diet high in saturated fat increases breast cancer risk, and most conspicuously, it suggests that saturated fat intake is involved in the causation of three subtypes of breast cancer,” said study researcher Sabina Sieri, of the National Cancer Institute in Milan. The study does not point to a specific “threshold” level of fat intake that raises a woman’s risk of breast cancer, she said.
However, Sieri recommended that calories from saturated fat should not exceed 10 percent of a person’s daily diet.
For a woman who consumes 2,000 calories a day, that means that no more than 200 calories should come from the saturated fats found in meats, cheese, butter, or processed foods.
Women in the study completed dietary and lifestyle questionnaires at the study’s start. The researchers found that, after 11.5 years, 10,062 women in the study (about 3 percent) had breast cancer, and noted the type of breast cancer each woman had. Higher fat consumption was linked with a greater risk of the types of breast cancer that are fueled by hormones, such as estrogen receptor-positive breast cancer.
The women in the study who ate the most saturated fat (about 47.5 grams per day) had about a 28 percent increased risk of these types of breast cancer, compared with the women who ate the least saturated fat (about 15.4 grams per day).
The results of past studies examining the association between high fat consumption and breast cancer risk have been conflicting, Sieri told Live Science. It’s difficult, she said, for researchers to get accurate information on fat consumption, and people living in different regions may tend to consume different types of fat.
In the new study, the researchers addressed the fact that breast cancer is now classified clinically into three subtypes. “Each subtype,” Sieri said, “has its own prognosis and set of risk factors, which may have also contributed to inconsistences in previously published reports.”
The new study is published online on April 9 in the Journal of the National Cancer Institute.
“This research is impressive because it recognizes that breast cancer is not a single disease, and previous studies [of saturated fat] have overlooked that,” said Dr. Kim M. Hirshfield, a medical oncologist at Rutgers Cancer Institute of New Jersey.
Although the study indicates that as more saturated fat is consumed, the risk of breast cancer steadily rises, Hirshfield said that further studies are needed to determine the amount of saturated fat women can safely consume as part of a healthy daily diet.
“For optimal breast health, and for overall health benefits in general, it is recommended that women consume saturated-fat calories closer to the lower end of the spectrum in the study, which is around 15 grams a day,” Hirshfield said.