A report published last week in the journal Cancer has concluded that eating more fibre-rich foods, especially ones high in soluble fibre, helps guard against breast cancer. Fibre’s protective effect was seen in both premenopausal and post-menopausal women.
We’ve been told for years to increase our daily fibre intake. A high-fibre diet has long been tied to preventing constipation, controlling body weight and guarding against type 2 diabetes, cardiovascular disease and colorectal cancer.
When it comes to breast-cancer risk, studies investigating fibre intake have, so far, been inconsistent. And very few studies have evaluated the effect of fibre from different foods, or whether fibre protects against breast cancer in premenopausal women.
About the new study
For the analysis, researchers from the Harvard T.H. Chan School of Public Health combined data from 20 large prospective studies, published before July of 2019, on fibre and breast-cancer risk.
Compared to women who had the lowest daily fibre intake, those whose diets provided the most were 8-per-cent less likely to be diagnosed with breast cancer. The reduction in risk was similar for all sources of fibre including cereal grains, vegetables, fruits and pulses (beans and lentils).
When the researchers investigated the effect of fibre on premenopausal and post-menopausal breast cancers separately, they found that a high-fibre diet reduced the risk of both by 18 per cent.
A high intake of soluble fibre (found in oats, oat bran, barley) was found to significantly lower breast-cancer risk. The findings, while not statistically significant, suggested that a diet high in insoluble fibre (found in wheat bran, vegetables, nuts) was also protective.
These risks, called relative risks, compare the likelihood of developing breast cancer between two groups of women; they do not apply to a woman’s individual risk. In Canada, a woman has a one-in-eight chance, or a 12.5-per-cent risk, of developing the cancer in her lifetime.
An 8-per-cent reduced risk, then, lowers a woman’s personal risk to 11.5 per cent from 12.5 per cent. An 18-per-cent reduced risk for a premenopausal (or post-menopausal) woman reduces a woman’s personal risk to 10 per cent from 12.5 per cent.
How fibre may protect
The studies included in the analysis were observational and, therefore, don’t prove that a high-fibre diet directly decreases breast-cancer risk . Measurement of fibre intake may also be prone to error if participants under-reported or overreported eating certain food groups.
Despite these limitations, there are several ways in which fibre may help guard against breast cancer. There’s long-standing evidence that fibre lowers circulating estrogen levels; being exposed to estrogen over a long period of time is thought to increase risk.
A high-fibre diet also helps control blood sugar, as well as insulin and insulinlike growth factors, hormones implicated in breast-cancer risk. And fibre nourishes the community of microbes that live in our gut, which plays an important role in regulating circulating estrogen.
Finding fibre in foods
To increase your daily fibre intake include fruits and vegetables in meals and snacks. Fibre-rich fruits include raspberries, blackberries, pears, apples, oranges, kiwi fruit, mango, dried apricots, avocado and pomegranate seeds.
Higher-fibre vegetable choices include snow peas, green peas, Swiss chard, broccoli, Brussels sprouts, bell peppers, butternut squash, cauliflower, carrots, collard greens and eggplant.
Choose whole grains instead of refined (white) grains, which have been stripped of fibre. High-fibre choices include bulgur, hulled barley, farro, freekeh, quinoa, black rice and whole-wheat pasta.
Include good sources of soluble fibre in your diet, too. These include black beans, lima beans, navy beans, kidney beans, Brussels sprouts, broccoli, sweet potato, avocado, apples, oranges, figs, strawberries, oatmeal, oat bran and psyllium.
Lowering breast-cancer risk goes beyond consuming more fibre. Research suggests that maintaining an overall healthy diet and lifestyle can help.
If you drink alcoholic beverages, limit yourself to one drink a day (e.g., five ounces of wine, 12 ounces of beer or 1.5 ounces of spirits). Even small amounts of alcohol may increase breast-cancer risk.
Maintain a healthy weight. Obesity increases the risk for breast cancer in post-menopausal women.
Be physically active. Women who are physically active have a lower risk of breast cancer than those who aren’t. The protective effects are similar in premenopausal and post-menopausal women.
Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.
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