Diet may play a role in preventing breast cancer, some observational studies have found. While such studies don’t prove cause and effect, eating more vegetables, more fibre and less red meat, for example, has been linked to a lower risk.
A study by California researchers released last week is the latest bit of evidence to suggest that diet can help fight breast cancer.
Researchers from the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center reported that eating a lower-fat diet, which included grains and plenty of vegetables and fruits, significantly cut the risk of dying from breast cancer in postmenopausal women.
The results, presented at the American Society of Clinical Oncology annual meeting in Chicago, are preliminary until the study is published.
The study is the latest analysis of the Women’s Health Initiative (WHI) Dietary Modification trial, a study which began in the 1990’s when researchers assigned healthy women, ages 50 to 79, to a low-fat diet (20 per cent fat) or their usual diet (32 per cent fat). Women in the low-fat diet group were also asked to increase fruit and vegetable intake to five or more servings a day, eat at least six daily grain servings and limit high-fat meat and dairy products.
The study lasted for eight-and-one-half years. Women assigned to the low-fat diet didn’t hit the 20 per cent fat target, but they did modestly reduce fat intake and they increased their intake of grains, fruits and vegetables. They also changed their cooking methods and reduced meat and dairy intake.
When the trial ended in 2005, there were fewer newly diagnosed breast cancers and breast cancer deaths among women in the low-fat-diet group compared to the usual-diet group, but these findings weren’t statistically significant (i.e., they could have been a chance finding).
After the intervention, 85 per cent of the participants were enrolled in an extension study which tracked them for another 20 years. Women who were in the low-fat diet arm of the trial received quarterly mailings offering tips to maintain the low-fat dietary pattern.
The researchers found that women who were in the low-fat-diet arm during the original study were 21 per cent less likely to die from breast cancer compared with women who ate their usual diet.
The low-fat dietary pattern appeared to have an even greater effect on reducing breast cancer deaths in women with larger waist circumferences, elevated blood pressure, high cholesterol and/or diabetes.
These findings come from a randomized controlled trial – the strongest evidence for cause and effect – that involved nearly 49,000 women and included two decades of follow up. But they are not without caveats. The researchers don’t know to what degree these women maintained the low-fat dietary pattern during the follow up.
The diet modifications the women achieved during the intervention period weren’t dramatic; it’s quite possible that the participants were able to maintain such moderate diet changes. But we don’t know.
In the meantime, existing evidence supports adopting the following diet and lifestyle habits to help lower the risk of breast cancer.
Eat vegetables, fruit and whole grains every day. As part of a healthy diet, these foods offer fibre and phytochemicals (protective plant compounds), both thought to play a role in breast cancer prevention.
Include three (or more) cups of vegetables and two to three fruit servings in your daily diet. Eat a variety of colourful produce to consume a wide variety of phytochemicals.
Choose fibre-rich whole grains such as oats, freekeh, millet, quinoa, brown rice, spelt berries, wheat berries and 100-per-cent whole grain pastas and breads.
Eat less red meat. Some research has linked eating too much red meat, especially well-done red meat, to a higher risk of breast cancer.
Limit red meat to three meals a week. Replace red meat with other sources of protein, such as chicken, fish, beans and lentils or nuts.
Limit or avoid alcohol. Even small amounts of alcohol increase breast cancer risk. Limit yourself to no more than one drink a day. (One drink is equivalent to five ounces of wine, 12 ounces of beer or 1.5 ounces of hard liquor.)
Maintain a healthy weight. Obesity is a known risk factor for breast cancer, especially so after menopause and for women who put on extra weight in adulthood. If you’re at a healthy weight, be vigilant to keep it there. If you’re carrying extra weight, take steps to lose some.
Be physically active. Many studies have found regular exercise helps guard against breast cancer. Aim for at least 150 minutes of moderate aerobic exercise or 75 minutes of vigorous aerobic activity each week.
Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.
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