Increased fiber in young adulthood may lower breast cancer risk

1. Increased dietary fiber consumption in adolescence and young adulthood was associated with a decreased risk of breast cancer, especially premenopausal cases.

2. Considering specific fiber types, increased fruit and vegetable fibers were most strongly associated with a decreased breast cancer risk.

Evidence Rating Level: 1 (Excellent)

Study Rundown: High blood estrogen level is a known risk factor for breast cancer. Thus, factors that decrease circulating estrogen may be protective. Although it is believed that dietary fiber inhibits estrogen reabsorption, previous studies have failed to demonstrate a significant link between fiber consumption and breast cancer risk. The majority of these reports, however, did not consider the impact of fiber intake during adolescence and young adulthood. To investigate the role of dietary fiber intake during the early female reproductive years on future breast cancer development, this study analyzed food frequency questionnaires and self-reported breast cancer cases from individuals in the Nurses’ Health Study II cohort. Adjusting for covariates including family history of breast cancer and parity, results demonstrated a significant trend for decreased risk of breast cancer with increased fiber intake in young adulthood (27 to 44 years of age). A similar but weaker trend was observed for dietary fiber consumed in high school. When different fiber types (cereal, fruit, vegetables, and legumes) were considered individually, fruit and vegetable fibers appeared to be the most protective. Although this study was highly powered, the possibility for additional confounding factors and response bias cannot be ignored. Despite these limitations, the results emphasize the importance of clinicians, and society as a whole, encouraging children and young adults to maintain a healthy diet from an early age.

Click to read the study, published today in Pediatrics

Relevant Reading: Dietary fiber and breast cancer risk: a systematic review and meta-analysis of prospective cases

In-Depth [prospective cohort]: Participants included 2 subsets of the 116 430 females in the Nurses’ Health Study II (NHSII) who were aged 25 to 42 at enrollment in 1989. Data from 90 534 women who met exclusion criteria and completed the 1991 food frequency questionnaire (FFQ) were used to assess the impact of fiber intake during early adulthood while fiber intake during adolescence was analyzed from data of 44 263 women who returned a supplemental FFQ in 1998. Food fiber content was determined from information provided by the US Department of Agriculture, food manufacturers, and independent academic sources, and breast cancer cases were documented via biennial NHSII questionnaires. After controlling for age, race, family history of breast cancer, and parity, results demonstrated a significant inverse trend of association across quintiles between fiber intake and breast cancer development (adolescence: P_trend = 0.04; early adulthood: P_trend = 0.002). This significant trend also held true for premenopausal cases considered separately (adolescence: P_trend = 0.04, early adulthood P_trend = 0.008). Of the 4 specific fiber types analyzed, the strongest trends of association with decreased breast cancer risk were found with increased fruit fiber and vegetable fiber (P_trend = 0.06; P_trend = 0.04). Treating fiber intake as a continuous variable, it was estimated that for every 10 g/day fiber increment increase in consumption during adolescence or early adulthood, risk of breast cancer decreased by 14% and 13%, respectively.

Image: PD

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