There are now over 3 million US breast cancer survivors, with the number of survivors only expected to increase in the years ahead. Today, a new report identified potential links oxn how diet, activity, and weight may affect survival for women diagnosed with breast cancer.
Diet, Nutrition, Physical Activity and Breast Cancer Survivors is part of an ongoing, systematic review called the Continuous Update Project (CUP). It’s the most rigorous analysis of the research on diet, weight and physical activity for breast cancer survivors, and it’s the first time a CUP report has focused on survivorship.
Here, Anne McTiernan, MD, PhD, the panel lead of this CUP report and researcher at the Fred Hutchinson Cancer Research Center in Seattle, talks about the report’s findings and what it means.
Q: What did the CUP report look at?
A: The report looked at associations between specific diet patterns and components, weight, and physical activity with mortality from all causes, mortality from breast cancer, and incidence of secondary breast cancer. This report did not look at associations of diet, physical activity, or weight with quality of life, fatigue and many other issues in which lifestyle factors may play a role.
Q: Why is that?
A: Studies have used very different definitions of breast cancer recurrence, and therefore it’s very difficult to combine studies together in a meaningful way.
Q: Most studies were related to body fat. Can you talk about the findings?
A: For breast cancer survivors, there is an association between women who are overweight or obese being more likely to die from their breast cancer or from any cause than survivors who are normal weight. This has been found from studies around the world and from many populations. Most studies looked at a measure called Body Mass Index, or BMI, which is weight corrected for height. Associations with higher mortality were seen for higher BMI both before and after diagnosis of breast cancer.
Q: Yet the evidence was not strong enough to say there was a definitive link, correct?
A: True. The association was not enough to base a public health recommendation on because it could be due to other influences called “confounders” that may also have affected mortality. For example, obese survivors may have other conditions (comorbidities), or receive an under-dose of chemotherapy, which may contribute to the increased mortality observed.
Q: For diet, can you explain the evidence related to fiber and soy?
A: The report found an association between eating high intake of foods containing fiber, such as vegetables, fruits, and whole grains, and reduced risk of dying from any cause. This dietary association was found both before and after diagnosis. There was an association between eating higher amounts of foods containing soy or isoflavones after diagnosis and lower risk of all-cause mortality. For soy and isoflavones – which are components of soy – food sources are most likely healthier than supplements.
Q: There was also an association – not convincing – for physical activity and longer survival. From this and studies on quality of life, what is the message?
A: Systematic reviews of quality of life and breast cancer survivors have shown that short-term gym-based aerobic exercise programs improve survivors’ quality of life and general well being. There is limited information about effects of programs longer than a few months, or about effects of exercising on your own. We don’t have definitive studies on the health effects of other types of exercise programs. It does suggest that breast cancer survivors might feel better if they exercise, especially if the exercise is aerobic/ Examples of aerobic exercise include walking, biking, hiking, running, and elliptical machines.
Q: What’s the message here to breast cancer survivors?
A: The first important message is to try not to gain weight during treatment. Medication, and changes in women’s ability and desire to exercise and eat healthy mean that many may gain weight during treatment. Even with the associations found, we can’t say that any particular diet or weight loss will prolong survival, yet there is no known harm to overweight breast cancer survivors losing weight in a healthy way.
Q: What is a healthy way?
A: Reducing calories, being physically active, and paying attention to the quality of the diet can help survivors achieve a healthy weight. When women are ready and interested, making certain lifestyle changes have been shown to reduce weight. These include: reducing dietary calories and fat, writing down everything eaten, counting calories, decreasing high-calorie drinks, decreasing energy dense foods, increasing intake of clear soups and salads, and weighing at least weekly.
I would suggest that breast cancer survivors follow the AICR Recommendations for Cancer Prevention, but that they check with their doctors for what specific lifestyle changes are appropriate for them.