Higher Intake of Fiber May Protect Against Breast Cancer

Lara C. Pullen, PhD

February 03, 2016

A higher intake of fiber, particularly during adolescence and early adulthood, appears to reduce the risk for breast cancer, according to an analysis of data from the Nurses' Health Study II published online February 1 in Pediatrics.

"The associations were apparent for most sources of fiber and were independent of other dietary factors and healthy eating behavior," Maryam S. Farvid, PhD, from Harvard University in Boston, Massachusetts, and colleagues report.

The ongoing prospective study includes registered nurses aged 25 to 42 years at enrollment in 1989. The large cohort had 90,534 premenopausal women who completed a dietary questionnaire in 1991 and 44,263 women who completed a questionnaire in 1998 that asked them to remember their diet in high school.

The investigators specifically evaluated the importance of timing of fiber intake on risk for premenopausal breast cancer. They thus assessed the association between fiber intake during specific periods of life (adolescence, early childhood, and premenopause in general) and breast cancer risk.

The researchers found an inverse association between consumption of most sources of fiber and incidence of breast cancer. Specifically, when women in early adulthood in the highest quintile of fiber intake were compared with those the lowest quintile of fiber intake, the relative risk for breast cancer was 0.81 (95% confidence interval, 0.72 - 0.91). This represented a difference between 12.0 g of fiber per day in early adulthood in the lowest quintile and 26.4 g of fiber/day in the upper quintile.

When the analysis was performed for average fiber intake during adolescence and early adult life, the relative risk for highest vs lowest quintiles of fiber consumptions was 0.75 (95% confidence interval, 0.62 - 0.91).

Is Diet a Modifiable Risk Factor for Breast Cancer?

Recently, several studies have suggested that dietary fiber may be protective against breast cancer, although the effect documented in the previous studies was, in general, small. The current study is distinctive in that it specifically examined diet during adolescence or early adulthood and related these dietary habits to later cancers.

Taken together, the studies suggest that fiber is a potentially modifiable risk factor for breast cancer. Fiber consumption may be particularly important during adolescence or early adulthood, when breast cancer risk factors appear to be especially important. The researchers suggest in their discussion that dietary fiber may reduce breast cancer risk by improving insulin sensitivity and decreasing insulin-like growth factors.

"[The authors] used rigorous methodology to attempt to control for confounding factors, and although there may be confounding dietary or lifestyle factors also contributing to these findings, the associations are interesting and deserve further study," write Kathleen K. Harnden, MD, and Kimberly L. Blackwell, MD, from Duke University Medical Center in Durham, North Carolina, in an accompanying editorial.

"In particular, the association between dietary fiber and weight must be examined prospectively to understand the clinical impact of the authors' findings. It is reasonable for pediatricians to encourage a high-fiber diet and include decreasing breast cancer risk as one of the potential benefits."

The authors, Dr Harnden, and Dr Blackwell have disclosed no relevant financial relationships.

Pediatrics. Published online February 1, 2016. Article full text, Editorial full text

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