TEHRAN (Iran News) – A random-effects meta-analysis of prospective observational studies, published in Cancer, found that high total fiber consumption was correlated with a reduced risk of breast cancer.

Additionally, the results suggested that dietary fiber intake may decrease the risk of both premenopausal and postmenopausal breast cancers, cancernetwork.com reported.

“The reduction in risk appears to be similar for the intake of all sources of fiber (cereal, fruit, vegetable, and legume), although statistical significance was not reached, except for fruit fiber,” the authors wrote. “A high intake of fiber was [also] found to be inversely, but not significantly, associated with ER+/PR+ and ER-/PR- breast cancers.”

Researchers searched the MEDLINE and Excerpta Medica dataBASE (EMBASE) through July 2019 for prospective studies that reported on the association between fiber consumption and incident breast cancer. The pooled relative risk (RR) and 95 percent confidence intervals (CI) were then estimated by comparing the highest versus the lowest category of total and types of fiber consumption, using a random-effects meta-analysis.

According to the study, in the US, dietary fiber usually comes from whole grains and cereals (44.8 percent), vegetables (22.6 percent), fruits (11.1 percent), legumes, nuts, and seeds (7.2 percent), and other foods (14.3 percent). Given this substantial contribution of fiber sources to the American diet, the researchers expanded the analysis to include the intake of these different dietary sources of fiber as exposure variables.

Overall, the researchers identified 17 cohort studies, two nested case-control studies, and one clinical trial study. Total fiber consumption was found to be associated with an 8 percent lower risk of breast cancer (comparing the highest versus the lowest category, pooled RR, 0.92; 95 percent CI, 0.88-0.95 [I2 = 12.6 percent]). Moreover, soluble fiber was significantly inversely associated with risk of breast cancer (pooled RR, 0.90 [95 percent CI, 0.84-0.96; I2 = 12.6 percent]) and insoluble fiber was suggestively inversely associated with risk of breast cancer (pooled RR, 0.93 [95 percent CI, 0.86-1.00; I2 = 33.4 percent]).

Higher total fiber intake was correlated with a lower risk of both premenopausal and postmenopausal breast cancers (pooled RR, 0.82 [95 percent CI, 0.67-0.99; I2 = 35.2 percent] and pooled RR, 0.91 [95 percent CI, 0.88-0.95; I2 = 0.0 percent], respectively). Further, the researchers observed a nonsignificant inverse association between intake of total fiber and risk of both estrogen and progesterone receptor-positive and estrogen and progesterone receptor-negative breast cancers.

“Several biological mechanisms may explain the beneficial effects of dietary fiber on breast cancer risk. Fiber may decrease incident breast cancer by controlling blood glucose and improving insulin sensitivity,” the authors wrote. “In addition, fiber may increase serum concentrations of sex hormone-binding globulin, as well as affect the composition of intestinal microbiota and inhibit colonic β-D-glucuronidase activity. Thereby, dietary fiber may reduce deconjugation and reabsorption of estrogen, and then reduce circulating levels of estrogen.”

Notably, because the associations between fiber intake and breast cancer were evaluated mainly using prospective studies in North American and Europe, the findings may not be generalizable to other geographic regions, which may differ across racial, ethnic, socioeconomic, and cultural factors. Additionally, the amounts in fiber intake in the highest and lowest categories were not consistent across studies.

“Although we found inverse associations between intake of different sources and type of fiber and breast cancer risk, only soluble fiber and fruit fiber demonstrated significant associations,” the authors wrote. “The current study findings support the American Cancer Society’s dietary guidelines to consume foods rich in total fiber, including fruits, vegetables, and whole grains.”