Soy Based Foods / Nutritional Supplements for Women with Breast Cancer

By Trish Kopan BScPharm & John Mackey MD

Many people who are diagnosed with cancer want to do as much as they can to improve their health. There has been increased interest about changing food intake to improve health. Much of the information available about food supplements is not necessarily helpful or scientifically sound. The purpose of this ‘Hot Topic’ is to talk about what is known at this time about soy based foods for women with breast cancer.

The media, health food stores, and popular magazines advise women to increase their intake of soy or soy protein. This is because soy and other plant-based foods like cereal grains contain isoflavones, which may contain phytoestrogens (plant estrogens). These phytoestrogens are thought to have both protective and stimulatory effects on breast cancer. These substances are also thought to help with hot flashes that some women find bothersome. Consumption of soy foods is considered to be safe as part of a healthy and balanced diet, since foods like soybeans or cereal grains have been a main source of protein for people for thousands of years. Some studies suggest this might explain why in some countries where soy foods are part of the daily diet, women have less menopausal problems such as hot flashes.

However, there are many food supplements available in a pill form. At this time, laws do not exist to make sure that these pills contain what they claim nor any safety information on the label. It is possible to take pills that have very little, if any of the labeled substance, or too much, causing overdose. It is also not known at this time how phytoestrogens or isoflavones might interact with medications like Tamoxifen.

Most doctors advise that women take soy foods as part of a complete and balanced diet, but to avoid supplement pills. If you would like more information about this topic or would like to know if this treatment would be helpful for you, talk to your doctor at the next clinic visit.

Resources

1. Seidl MM and Stewart DE. Alternative treatments for menopausal symptoms - systematic review of scientific and lay literature. Canadian Family Physician 1998 Vol 44: 1299 - 1308 June.
2. The Medical Letter, Volume 2 (Issue 1072), February 21, 2000
3. Pharmacist's Letter #161015 Soy and isoflavone supplements.
4. Love SM. Dr. Susan Love's Breast Book. 2nd ed. 1995 Addison Wesley.