Your mother always told you to eat your vegetables. A new study shows she was onto something, especially if you include fruits. A large study published in The BMJ earlier this year found that people who have diets filled with ultra-processed foods have a higher risk of cancer. Conversely, diets rich in fruits and vegetables seem to lower a person’s risk for breast cancer.
There has been other research pointing to a possible link between fruits and vegetables and lowered breast cancer risk, but other studies found the results to be inconclusive. However, this new study, conducted by researchers at the Harvard T.H. Chan School of Public Health in Boston, MA, was a large-scale, long-term investigation in more detail. It specifically looked at the relationship between fruits and vegetables in a person’s diet and their risk of breast cancer.
The study shows a correlation between eating lots of fruits and vegetables and lower incidence of breast cancer, but it also explains how much fruits and vegetables someone should have every day to get those benefits.
The Harvard team collected diet- and health-related data from female participants of two large population studies: 88,301 women from the Nurses’ Health Study that began in 1980 and 93,844 women from the Nurses’ Health Study II that began in 1991.
In those two studies, participants’ dietary habits were collected via questionnaires filled in every four years. Other information regarding risk factors for breast cancer — including age, body weight, smoking habits, and family history of cancer — was compiled through questionnaires every two years.
Analysis of the above data found that women who ate more than five and a half servings of fruits and vegetables daily had an 11 percent reduced risk of developing breast cancer, compared with women who ate two and a half servings or less of fruits and vegetables. One serving consisted of one cup of raw leafy vegetables, half a cup of either raw or cooked vegetables, or half a cup of raw or cooked fruit.
The Harvard team also wanted to explore whether eating fruits and vegetables was associated with different degrees of risk reduction for different types of breast cancer. To find this, they analyzed the data in a different way, splitting cancer type by receptor status and molecular subtype.
This found an interesting additional trend — diets rich in fruits and vegetables appeared to be associated with a particularly lowered risk of developing aggressive types of cancer tumors. These tumors grow quickly, spread easily, and can be resistant to traditional treatments, such as chemotherapy. These include estrogen receptor-negative breast cancer, HER2-enriched breast cancer, and basal-like cancers, which are similar to another aggressive tumor type called triple-negative.
The study’s first author, Maryam Farvid, commented on the findings. “This research provides the most complete picture of the importance of consuming high amounts of fruits and vegetables for breast cancer prevention,” she writes.
While the study didn’t delve into what may behind the lower breast cancer incidence with diets heavy in fruits and vegetables, it did theorize that fruits and vegetables contain other nutrients, such as antioxidants, that could be behind the lowered cancer risk.
“While a diet with lots of fruits and vegetables is associated with many other health benefits, our results may provide further impetus for women to increase their intake of fruits and vegetables,” writes senior author on the study Heather Eliassen.