A decades long study (from the Harvard T.H. Chan School of Public Health) had results that many women may find reassuring - because there may be something they can do to increase their odds of preventing breast cancer. The study found that women who ate more than 5.5 servings of fruits and vegetables each day had an 11% lower risk of breast cancer than those who ate 2.5 or fewer servings daily.
While the findings support eating a variety of fruits and vegetables, they found that cruciferous (broccoli, cabbage, cauliflower) and yellow/orange vegetables (e.g. winter squash) appear to be especially beneficial in reducing the risk of breast cancer, especially those that are more aggressive tumors. The association between amount of fruits and vegetables eaten daily and breast cancer appeared to be strongest 8 or more years before cancer diagnosis - meaning fruit and vegetable intake now appears to have effects many years later.
By the way, the researchers found in earlier research that a higher fiber intake (especially during adolescence and early adulthood) was also associated with a lower beast cancer risk. Now let's see if these findings hold up over time in other studies. From Science Daily:
Women who eat a high amount of fruits and vegetables each day may have a lower risk of breast cancer, especially of aggressive tumors, than those who eat fewer fruits and vegetables, according to a new study led by researchers from Harvard T.H. Chan School of Public Health. In their findings, cruciferous vegetables such as broccoli, and yellow and orange vegetables, had a particularly significant association with lower breast cancer risk.
"Although prior studies have suggested an association, they have been limited in power, particularly for specific fruits and vegetables and aggressive subtypes of breast cancer," said first author Maryam Farvid, research scientist in the Department of Nutrition. "This research provides the most complete picture of the importance of consuming high amounts of fruit and vegetables for breast cancer prevention." The study was published online July 6, 2018 in the International Journal of Cancer.
The researchers analyzed diet questionnaires submitted every four years by participants in the Nurses' Health Study (88,301 women, starting in 1980) and the Nurses' Health Study II (93,844 women, starting in 1991). Data on other potential breast cancer risk factors such as age, weight, smoking status, and family cancer history were taken from biennial questionnaires.
They found that women who ate more than 5.5 servings of fruits and vegetables each day had an 11% lower risk of breast cancer than those who ate 2.5 or fewer servings. (A serving is defined as one cup of raw leafy vegetables, half a cup of raw or cooked vegetables, or half a cup of chopped or cooked fruits.)
To find out whether the benefits of fruit and vegetable consumption differed among various types of breast cancers, the researchers conducted an analysis by tumor hormone receptor status and molecular subtype. They found that higher consumption of fruits and vegetables was particularly associated with lower risk of more aggressive tumors including ER-negative, HER2-enriched, and basal-like tumors.
Previous work by this research group linked reduced breast cancer risk with higher fiber intake, but the benefits of fruits and vegetables found in this study appear to be independent of their fiber content, according to the researchers. This suggests that other constituents of these foods, such as antioxidants and other micronutrients, may also be important in reducing breast cancer risk.