Diet Has Minimal Association With Breast Cancer Risk in Postmenopausal Women, Study Finds

Aside from alcohol, which was shown to have a strong positive correlation with breast cancer risk, none of the other main foods or nutrients examined in a recent study were strongly associated with breast cancer risk.

The role of diet in the incidence of breast cancer has been controversial. For many years, investigators have explored the role of diet, theorizing that certain products may increase or decrease the risk of developing breast cancer. Currently, the only dietary factor that shown evidence to increase the risk of breast cancer is alcohol. In this study, investigators analyzed the incidence of breast cancer among postmenopausal women based on dietary items and macronutrients thought to have prominent effects on breast cancer risk.

Eighteen dietary items and macronutrients were analyzed for any associations with invasive breast cancer, categorized separately according to estrogen receptor (ER) status. The dietary items included meat (type and quantity), fish, milk, cheese, yogurt, eggs, fruit, vegetables, and alcohol; the macronutrients included percentage of energy from protein, dairy protein, total fat, saturated fat, carbohydrate, free sugars, and dietary fiber.

The analysis included 691,571 women. After 12 years of follow-up, 29,005 women were diagnosed with invasive breast cancer, 10,838 who were ER-positive and 1658 who were ER-negative. As evidenced by previous studies, alcohol (per 10 g/day higher intake) was found to have a positive association with incidence of breast cancer (relative risk [RR], 1.08; 99% CI, 1.05-1.11, X₁² for trend = 62.1; P = 5.8 x 10^-14).

Specifically, the higher intake of alcohol was only associated with drinkers. In contrast, there was an inverse association of risk with fruit intake (RR, 0.94; 99% CI, 0.92-0.97, X₁² for trend = 29.4; P = 1.1 x 10^-6). The inverse association between fruit intake and breast cancer risk were seen with fresh (per 100 g/day higher intake) and dried fruit (per 10 g/day higher intake), but not with canned/stewed fruit or fruit juice.

Breast cancer risk was not associated with soy foods or any types of vegetables. Furthermore, none of the 8 macronutrients had any relation to breast cancer risk, except dietary fiber, per 5 g/day higher intake (RR, 0.91; 99% CI, 0.87-0.96, X₁² for trend = 20.5; P = 1.1 x 10^-4). Results after ER status was considered were similar between ER-positive and ER-negative women.

From this study, investigators concluded that alcohol has a strong positive association with breast cancer risk, although fruit and fiber have a weak inverse association with risk. Because high fruit and fiber intakes were correlated with normal weight women, casual confounding variables may lead to faulty conclusions. Thus, among the dietary items and macronutrients tested, only alcohol was shown to have any correlation with breast cancer risk.

Reference

Key TJ, Balkwill A, Bradbury KE, et al. Foods, macronutrients and breast cancer risk in postmenopausal women: a large UK cohort [published online November 8, 2018]. Int J Epidemiol. doi: 10.1093/ije/dyy238.