January 21, 2019
Diet and Breast Cancer: An Update

Diet and Breast Cancer: An Update

by Berkeley Wellness  

Most experts suspect that plant-based diets—or at least certain elements of them—reduce the risk of some cancers, but this has been sur­prisingly hard to prove (see Fruit vs. Cancer? Yes, No, Maybe). The strongest evidence concerns plant-based diets for the prevention of colorectal cancer.

It has been particularly hard to pin­point any dietary changes that will reduce the risk of breast cancer, other than diets that help control weight (since obesity increases the risk of postmenopausal breast cancer) and ones that include little or no alcohol. Two observational studies in the American Journal of Clinical Nutrition (AJCN) may offer some new clues, how­ever, about the benefits of plant-based diets for breast cancer.

Carotenoid-rich fruits and vegetables and breast cancer

A Harvard study analyzed data from nearly 33,000 female nurses over a 20-year period and found that those who had high blood levels of carotenoids—notably beta carotene, alpha caro­tene, and lycopene—were less likely to develop breast cancer, have a recurrence of the disease, or die from it. Measuring blood levels of certain nutrients is considered a relatively accurate way to assess food intake. Previous studies on carotenoids and breast cancer have had conflicting results, perhaps in part because most relied on dietary recall, which is subject to inaccuracy.

In a previous report, the same researchers analyzed eight earlier studies and also found that higher blood levels of carotenoids were associated with lower risk, but only for estrogen receptor-negative breast cancer, the less common type. The best sources of carotenoids are red, orange, and yellow fruits and vegetables (such as tomatoes, car­rots, sweet potatoes, melons, and peppers) as well as leafy greens.

Plant-based dietary pattern and breast cancer

Most studies on diet and cancer have focused on specific nutrients or foods, but in recent years researchers have been paying increased attention to overall dietary pat­terns instead. In the second AJCN paper, researchers used data from two large Cana­dian studies to evaluate the role of dietary patterns in breast cancer risk. Despite some inconsistencies, it found that a largely plant-based diet (focusing especially on vegetables and beans) was associated with reduced risk, while a “red meat and potato” dietary pattern seemed to elevate the risk. The researchers controlled for body weight, calorie intake, family history of cancer, and other factors. A systematic review in Nutrition Reviews similarly concluded that plant-based dietary patterns, including Mediterranean diets, may reduce the risk of breast cancer.