In my work in oncology nutrition, I’ve heard these five statements from both patients and healthcare providers alike. Following are brief explanations to help clarify what’s sensible and evidence-based, versus what’s unfounded.
1. “Women who have had breast cancer should avoid soy.”
Fears that soy foods increase breast cancer growth are not supported by evidence from large human studies. Soy is indeed rich in isoflavones, a kind of “plant estrogen.” However, eating whole soy foods, such as tofu or edamame does not cause a rise in the body’s circulating estrogens, nor does it increase risk for breast cancer or recurrence. Choose soy foods in moderation as part of an overall healthful diet. Limit highly processed foods that contain ingredients such as soy protein concentrate, and avoid soy isoflavone supplements (e.g. pills, powders), which have not yet been adequately studied for safety.
2. “Juicing helps fight breast cancer.”
Diets rich in plant foods including a variety of whole vegetables and fruits are associated with reduced risk for cancer and other illnesses. Upping the ante with large quantities of juice doesn’t confer more of a benefit, though. Too much juicing can wreak havoc with glycemic control and potentially interfere with certain breast cancer treatments.
3. “It’s a good idea to eat more calories before and during chemotherapy to gain a little extra weight.”
During adjuvant chemotherapy for breast cancer, women are actually more likely to gain than lose weight. And because weight gain may increase risk for breast cancer recurrence as well as a host of other chronic diseases such as type 2 diabetes and heart disease, it’s a good idea to prevent extra pounds before they become a problem. Weight gain during treatment is probably due to a number of factors, including increased “comfort” or “emotional” eating, decreased physical activity, fatigue and increased eating to help quell nausea. Most women shouldn’t intentionally eat to gain. An individual who maintains a healthy body weight should aim to stay at or near that weight. For a patient who is overweight, working with an RDN on gradual and sustained weight reduction may be prudent. A smart, balanced, non-restrictive diet and medically appropriate physical activity are safe and feasible during treatment.
4. “Dairy increases breast cancer risk.”
There’s no evidence to support this claim. Both quantity and quality matter. Practical portions of dairy foods help create satisfying meals within a mostly plant-based diet: think plain yogurt with fresh fruit and nuts, or grated hard cheese over a salad. Choosing organic dairy means the product was made from animals who were not given antibiotics or hormones to stimulate growth.
5. “If you already have breast cancer, it doesn’t matter what you eat anymore.”
No, no, no! Women should be encouraged not to throw in the towel on nutrition. Diet matters after breast cancer diagnosis as much as ever before. Eating healthfully can boost energy level, improve quality of life and mood, decrease side effects and complications from treatment, minimize the need for additional medications, and even reduce risk for cancer recurrence.