We're told repeatedly to get more fibre. It's advice that can keep you regular and help ward off heart disease, type 2 diabetes and possibly colon cancer. Now, according to a new study published in the September issue of the American Journal of Clinical Nutrition, increasing your intake of fibre can guard against breast cancer.
More than two decades ago, scientists hypothesized that dietary fibre could reduce breast cancer risk based on findings that vegetarian women had lower levels of the female hormone estrogen compared to their meat-eating peers. (It's thought that the female hormone estrogen promotes the growth of mutated breast cells.)
Fibre is also believed to guard against breast cancer by curbing the effects of insulin resistance and insulin-like growth factors, both of which have been linked to a greater risk of the disease. (Insulin-like growth factors are hormones thought to stimulate the growth of breast cancer cells.)
Some - but not all - studies have found that a higher fibre diet reduces breast cancer risk. These mixed findings may be due to the fact that only certain types of fibre - rather than total fibre - protect from the disease.
Fibre's protective effect may also differ by breast cancer hormone receptor status. Studies examining the effect of fibre on total breast cancer would miss this association.
Doctors test breast cancer cells to see if they have hormone receptors. Hormone receptor-positive tumours are fuelled by the female hormones estrogen and progesterone. Hormone receptor-negative cancer cells are not affected by estrogen and progesterone.
The current study - the largest of its kind - set out to determine the link between fibre intake and breast cancer by hormone receptor status in 185,598 postmenopausal women aged 50 to 71 years.
After seven years of follow up, women who consumed the most fibre (26 grams per day) were 13 per cent less likely to be diagnosed with breast cancer than women who consumed the least (11 grams per day). The official daily recommended intake for fibre is 25 grams for women aged 19 to 50 and 21 grams for older women.
A higher fibre diet was linked to a significantly lower risk of ER/PR-negative tumours, but not ER/PR-positive tumours. Women whose diets provided the most versus the least fibre had a 44 per cent lower risk of developing hormone-negative breast cancer.
Soluble, but not insoluble, fibre intake was protective from breast cancer. Both types of fibre are always present in varying proportions in plant foods, but some foods are rich in one or the other.
Soluble fibre dissolves in water. Once consumed, the fibre forms a gel in your stomach and slows the rate of digestion and absorption.
Soluble fibre has been shown to be more effective than insoluble fibre at controlling blood sugar, insulin and insulin-like growth factors, all of which have been linked to a greater risk of breast cancer. Insulin may impact breast cells directly or increase the growth of cancerous cells.
This study adds to a growing body of evidence that diet has a stronger effect on reducing the risk of hormone-negative breast cancer than hormone-positive tumours.
Current evidence suggests that the following nutrition strategies may guard against the disease.
Boost soluble fibre
Add soluble-fibre-rich food to your daily diet such as oats, oat bran, psyllium-enriched breakfast cereals, barley, legumes, citrus fruit and apples.
Choose low-glycemic carbs
Postmenopausal women whose diets contain mainly slow burning, or low-glycemic carbohydrates, have been found to have a lower risk of breast cancer, especially estrogen-negative tumours, compared to women who eat mainly high-glycemic carbohydrates.
High-glycemic foods such as white bread, refined breakfast cereals and sugary drinks lead to higher blood glucose and insulin levels, which in turn increase breast cancer risk.
Low-glycemic choices include grainy breads, brown rice, pasta, sweet potato, bran cereals, steel-cut or large flake oatmeal and most types of fruit.
Studies suggest that consuming 1 to 2 tablespoons of ground flaxseed each day helps reduce breast cancer risk. Natural compounds in flaxseed are able to bind to estrogen receptors on breast cells and, in so doing, block the action of the body's own estrogen on breast cells.
Add ground flaxseed to hot cereal, yogurt, smoothies, applesauce and baked-good recipes.
Curb fat intake
The Women's Health Initiative Dietary Modification Trial, the largest long-term trial ever conducted, found that a 20 per cent fat diet reduced the risk of breast cancer most notably in women who had a high fat intake at the start of the study.
A low-fat diet has also been shown to improve survival in women diagnosed with estrogen-negative breast cancer.
To reduce fat intake, choose skim milk, yogurt with 1 per cent milk fat or less and cheese with 15 per cent or less. Choose lean, skinless poultry, fish and beans more often than meat. Use added fats and oils sparingly.
Several studies hint that cruciferous vegetables such as broccoli and cauliflower are protective from breast cancer. These vegetables contain phytochemicals that help rid the body of carcinogens by regulating detoxification enzymes in the liver.
Cruciferous vegetables include bok choy, broccoli, broccoli sprouts, broccoflower, broccolini, Brussels sprouts, cabbage, cauliflower, rutabaga and turnip.
Limit or avoid alcohol
The evidence is convincing that alcohol, even in moderation, increases breast cancer risk. The Million Women Study published in 2009 found that for every additional drink consumed per day, the risk of breast cancer jumped by 12 per cent. Wine, beer and spirit increased the risk equally.
Alcohol may make breast cells more vulnerable to the effects of carcinogens or it may enhance the liver's processing of these substances. Alcohol may inhibit the ability of cells to repair faulty genes and may also increase estrogen levels.
If consumed at all, limit your intake to one drink per day or 7 per week.
Control weight Gaining weight after menopause is clearly linked with a higher risk of breast cancer. Obesity is thought to influence a woman's risk by increasing circulating estradiol, the most potent form of estrogen in the body.
Take steps to avoid or limit adult weight gain and increases in waist circumference. If you are overweight or have gained weight since menopause, take action to lose excess weight.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.