For patients with breast cancer, physical activity and avoiding weight gain are the most important lifestyle choices that can reduce the risk of cancer recurrence and death, according to an evidence-based review published in CMAJ (Canadian Medical Association Journal).

"Of all lifestyle factors, physical activity has the most robust effect on breast cancer outcomes," writes Dr. Ellen Warner, Sunnybrook Health Sciences Centre, Toronto, Ontario, with coauthor Julia Hamer. "Weight gain of more than 10% body weight after a breast cancer diagnosis increases breast cancer mortality and all-cause mortality. However, there are good reasons to discourage even moderate weight gain because of its negative effects on mood and body image," the authors state.

The review of 67 published articles looks at a variety of lifestyle factors, such as exercise, weight, diet, smoking and more, and examines the changes women can make to improve their chances of survival and reduce the risk of cancer recurring. About one-quarter of women diagnosed with early stage disease will eventually die of later metastases.

As the review contains practical recommendations of interest to patients, their families, physicians and other health care professionals, it is open-access and freely available to a global audience.

While evidence is inconclusive on the impact of some lifestyle behaviours, such as specific diets, alcohol consumption and vitamin supplements, the authors have summarized easy-to-follow key findings and unanswered questions in charts.

Key findings:

Avoid weight gain -- weight gain during or after breast cancer treatment is linked to breast cancer-related death. Women who are overweight or obese at diagnosis also have poorer prognoses.

Exercise -- patients should engage in at least 30 minutes of moderate exercise a day, five days a week, or 75 minutes of vigorous exercise per week. Two to three sessions of strength training for large muscle groups are also recommended.

Diet -- no specific type of diet has been shown to reduce the risk of breast cancer recurrence. Evidence indicates that patients do not need to avoid soy, and it may help with weight management if used to replace higher-calorie meat protein.

Vitamin supplementation -- moderate consumption of vitamin C may be helpful although more evidence is needed. Vitamin D supplements may be taken to maintain adequate levels for bone strength, since chemotherapy and hormonal treatments can reduce bone density.

Smoking -- stop smoking. While it is unclear if stopping smoking after a breast cancer diagnosis affects recurrence, the risk of death from smoking-related health issues is a strong reason to quit.

Alcohol intake -- limiting consumption to one or fewer alcoholic drinks per day may help reduce the risk of a second breast cancer.

"Making positive lifestyle changes can also be psychologically beneficial to patients by empowering them, since the feeling of loss of control is one of the biggest challenges of a cancer diagnosis," write the authors.

Physicians can play an important role in helping patients make positive changes.

"Because it is common for patients to reduce their level of physical activity after a breast cancer diagnosis, it is important for health care professionals to promote and encourage exercise in this patient population," the authors write. "Simply receiving advice from an oncologist to exercise more has been shown to increase patients' level of activity."

An important point to emphasize is that the breast cancer patients in the studies showing the benefits of lifestyle changes were also receiving conventional anticancer therapy; lifestyle changes should never be used as a substitute for standard therapy.

The authors caution that these recommendations are not a silver bullet for all women with breast cancer. Some breast cancers have aggressive biology and will recur despite the most meticulous lifestyle behaviours.

"Patients should not be made to feel that inadequate lifestyle changes have led to recurrence of their cancer," they conclude.