High Fiber Intake Linked to

Reduced risk of Breast Cancer

Anthony J Brown, MD | 2nd October 2009

As total dietary fiber intake increases, the risk of breast cancer, primarily ER–/PR– tumors, decreases, according to study findings published in the American Journal of Clinical Nutrition for September.

“Although dietary fiber has been hypothesized to lower risk of breast cancer by modulating estrogen metabolism, the association between dietary fiber intake and risk of breast cancer by hormone receptor status is unclear,” lead author Dr. Yikyung Park, from the National Cancer Institute, Rockville, Maryland, and colleagues note.

“Our study,” the researchers point out, “is the first study to examine the association between dietary fiber and breast cancer by histological type.” The investigators analyzed data on 185,598 postmenopausal women (average age 62 years) enrolled in the National Institutes of Health—American Association of Retired Persons Diet and Health Study. A 124-item food frequency questionnaire was used to assess fiber intake at baseline.

During an average follow-up of 7 years, 5461 breast cancer cases were reported, including 2391 for whom data on hormone receptor status were available: 1641 ER+/PR+, 336 ER+/PR–, 48 ER–/PR+, and 366 ER–/PR–. Relative to the lowest quintile of total fiber intake, the highest quintile was associated with a 13% decreased risk of breast cancer (p for trend = 0.02), the investigators found.

Further analysis showed the association to be stronger for ER–/PR– tumors than for ER+/PR+ tumors. Comparing the highest quintile of total fiber intake with the lowest, the risk of ER–/PR– breast cancer fell by 44% (p for trend = 0.008), while the risk of ER+/PR+ tumors dropped by just 5% (p for trend = 0.47).

The researchers also noted that the effect of fiber intake on breast cancer risk varied by histological type. High fiber intake was linked to a 34% reduced risk of lobular tumors (p for trend = 0.04) compared with a 10% reduced risk for ductal tumors (p for trend = 0.10).

Although total fiber intake seemed to impact breast cancer risk, fiber intake from several food groups, including grains, vegetables, fruit, and beans, did not.

Soluble fiber intake was inversely linked to breast cancer risk, whereas insoluble fiber intake showed no association.

“It is possible that fiber type makes a difference in pathophysiologic processes related to breast cancer,” the authors speculate. “Soluble fiber has been shown to be more effective in controlling blood glucose, insulin, and insulin-like growth factors, which have been positively related to risk of breast cancer.”

The association between total fiber intake and breast cancer risk was not significantly modified by total fat intake, the researchers report.

“Our finding suggests that dietary fiber can play a role in preventing breast cancer through nonestrogen pathways among postmenopausal women,” the researchers conclude. “Nevertheless, the totality of evidence at this point is far from consistent, and additional research is needed before definitive public health recommendations for fiber and breast cancer can be made.”

Clinical Context

Breast cancer is a hormone-related malignant tumor, and dietary factors such as fat and alcohol intake have been shown to be risk factors for breast cancer. Observational studies on the role of fiber in breast cancer have been equivocal, with some showing no association and others showing a protective effect. Some of this inconsistency may be related to the type of fiber (soluble vs nonsoluble, or source of fiber) and the histologic type of breast cancer studied.

This is a large prospective study of women in the National Institutes of Health-American Association of Retired Persons Diet and Health Study to examine the association between fiber intake, type of fiber, and type of breast cancer in postmenopausal women.

Study Highlights

  • The National Institutes of Health-American Association of Retired Persons Diet and Health Study was initiated in 1995 to 1996 with a cohort of 567,169 women aged 50 to 71 years from 6 US states and 2 metropolitan areas.
  • Excluded were women with prevalent cancer at baseline, end-stage renal disease, or implausible dietary intakes on self-report.
  • At baseline, dietary intake was assessed with a 124-item food frequency questionnaire with intake and portion size of foods during the previous 12 months.
  • There were 10 predefined frequency categories ranging from never to 6 times daily or more for beverages and from never to 2 or more times daily for solid foods.
  • There were 3 categories for portion size defined by Pyramid Servings Database using the 1994-1996 Continuing Survey of Food Intake by Individuals.
  • The food frequency questionnaire used was calibrated using 2 nonconsecutive 24-hour dietary recalls.
  • Breast cancer cases were identified through linkage with 11 state cancer registries and were able to identify 90% of cases in the cohort.
  • Histologic features of breast cancer were obtained from the cancer registries, and tumor estrogen (ER) and progesterone (PR) receptor status was available.
  • Breast cancer was classified as ductal, lobular, ductal-lobular, and other tumor.
  • Mean age at baseline was 62 years, 90% were white non-Hispanic, mean body mass index was 27 kg/m2, and two thirds were menopausal before age 50 years.
  • Women in the highest quintile of dietary intake (26 g/day) were more likely than those in the lowest quintile (11 g/day) to be physically active, use hormone replacement therapy, never to have smoked, and to consume less alcohol and fat and more fruits and vegetables.
  • At 7 years of follow-up, there were 5461 cases of incident breast cancer.
  • 3531 were ductal tumors, 550 were lobular tumors, 424 were ductal-lobular tumors, and 956 were other tumors.
  • There were 1641 ER+/PR+ tumors, 336 ER+/PR– tumors, 48 ER–/PR+, 366 ER–/PR– tumors, and 950 with unknown receptor status.
  • Dietary fiber intake was inversely associated with the risk for breast cancer (relative risk [RR], 0.87; P for trend = .02) for the highest vs the lowest quintile of intake.
  • However, this association was significant only for ER–/PR– tumors and ER– or PR– tumors.
  • The RR was 0.59 for ER– tumors, 0.64 for PR– tumors, and 0.56 for ER–/PR– tumors (P for trend = .008) vs ER+/PR+ tumors.
  • For every 10-g/day of fiber intake, the age-adjusted RR of ER–/PR– tumors was 0.83, and after correction and adjustment, the RR was 0.70 (ie, 30% lower risk).
  • The associations were significantly different for ER+/PR+ tumors vs ER–/PR– tumors (P = .05).
  • The inverse association between fiber intake and breast cancer was more strongly related to ER negativity vs histologic type.
  • After adjustment, there was no significant association between fiber intake and type of breast cancer: ductal vs lobular vs ductal-lobular.
  • The source of fiber (fruits, vegetables, grains, or beans) did not affect the association, but soluble fiber was inversely related to breast cancer, whereas insoluble fiber was not.
  • The association between fiber intake and breast cancer was not modified by fat or alcohol intake, body mass index, or menopausal hormone therapy.
  • The authors concluded that intake of soluble fiber was associated with a lower risk for ER– and PR– breast cancer but not with receptor-positive breast cancers.

Clinical Implications

  • Intake of soluble fiber is inversely associated with the risk for receptor-negative breast cancer in postmenopausal women.
  • The source of fiber is not associated with a reduced risk for breast cancer, and the association between fiber intake and breast cancer is not dependent on histologic type.