Soy, Flax, Hormones

February 16, 2012 by Dr. Kristi Wrightson

Soy, Flaxseed, and Hormones. Safe or Not?

Q: A breast imaging tech told my friend to be careful eating soy and flaxseed products as they interfere with estrogen production & could cause a cancer risk. I use soymilk in coffee and take flaxseed supplements. Should I be concerned? How much is too much?

A: Soy and flaxseeds are both extremely popular components in food today and can be found on ingredient lists down most grocery store aisles. The constituents of soy, called isoflavones, were made popular because of research started in the 1990s that touted significant benefits, such as decreasing cholesterol, risk of heart disease, menopausal symptoms and some cancers. Flaxseed is less well-known but has also been shown to have benefits very similar to soy, such as reducing cholesterol and high blood pressure and maintaining hormonal balance.(1)

The beneficial actions of soy on female hormones are due to the phytoestrogenic effect that soy isoflavones have on the estrogen receptors. The isoflavones mimic estrogen at the receptor site. However, the action is much weaker than that of the estrogens that your body produces. Because soy molecules bind to the receptor, they can also block the receptor and compete with stronger estrogen.

As well, flaxseed is widely used today for various reasons, specifically for benefits due to its high content of essential fatty acids. Flaxseed, like soy, is phytoestrogenic in the body.(2) The estrogenic molecule in flaxseed binds to the estrogen receptor in the body but does not stimulate any action; instead it acts as a blocker of the receptor.

Both soy and flaxseeds have been studied to prove protective effects against hormonally based cancers, such as breast and prostate. Recent studies have had varying success at proving that soy actually prevents breast cancer in the body. The most recent theory suggests that pre-pubertal exposure to soy reduces risk of the disease - while post-menopausal intake can increase the risk of cancer.(3)

Studies have a similar track record in proving flaxseeds efficacious in preventing cancer. However, the other benefits of the dietary supplement are convincing that it is safe and beneficial to overall health.

• Overall, soy seems to be a good, low-fat addition to a healthy diet. Dosages of fewer than 10 grams per day have been shown to be safe and even advantageous for overall health.(4)

• In addition, a supplement of flaxseeds to the diet, in moderation, can be beneficial to the body. According to the University of Maryland Medical Center, 1 tablespoon of oil or 3000 mg in capsules are a good dosage.

As with any supplement, consult your physician before starting any soy or flaxseed product, as they can have adverse effects if taken in certain conditions or with some medications.

Note added October 27, 2008: A Canadian study of expectant women taking herbal supplements reports that women taking flaxseed oil (not flax seed) in the last two trimesters of pregnancy were significantly more likely to have a premature delivery.(5)

- Dr. Kristi Wrightson, ND, MS, RD

Sources:

1. Harper CR, et al. “Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans.” Journal of Nutrition, Jan 2006;136(1):83-7. PMID:16365063.

2. Pruthi S, et al. (Mayo Clinic). “Pilot evaluation of flaxseed for the management of hot flashes.” Journal of the Society for Integrative Oncology, Summer 2007;5(3):106-12. PMID:17761129.

3. Duffy C, et al. “Implications of phytoestrogen intake for breast cancer.” CA, a Cancer Journal for Clinicians, Sep-Oct 2007;57(5):260-77. Review.

4. Messina M, et al. “Gaining insight into the health effects of soy but a long way still to go: Commentary on the fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease,” Journal of Nutrition, Mar 2002;132(3):547S-551S. Review.

5. "Canadian Data Indicate Expectant Mothers Taking Flaxseed Oil Increase Risk of Premature Birth."