Phytoestrogens


Phytoestrogens (plant oestrogens) are substances that occur naturally in plants. They have a similar chemical structure to our own body's oestrogen (one of the main female hormones), and are able to bind to the same receptors that our own oestrogen does.

Phytoestrogens behave differently to female oestrogen and this depends on the oestrogen's environment (whether a woman is in her reproductive years and has higher oestrogen, or is postmenopausal with lower oestrogen), how they bind to the oestrogen receptor and particularly to which oestrogen receptor they bind to.

Eating phytoestrogens can produce either some of the same effects as human oestrogen (oestrogenic effects) or opposed effects (anti-oestrogenic effects). Which effects are triggered depends on existing levels of oestrogen in the body and how the phytoestrogens bind to receptors in the body.

Key points
  • Eating foods rich in phytoestrogens is likely to be nutritious and provides protein, fibre, vitamins and minerals.
  • The effect of phytoestrogens on menopausal hot flushes varies between individuals, as only a third to a half of ondividuals have the gut bacteria that convert the phytoestrogens to a more potent form
  • There is growing evidence to suggest that phytoestrogens may help with bone and cardiovascular health, but this remains unclear.
  • It is not recommended that woman at high risk of breast cancer, or who have had breast cancer, take soy supplements

In a postmenopausal woman, (or during the perimenopause) when her own body's oestrogen is low, phytoestrogens may help ease the symptoms of low oestrogen in about one in three women. This is because about a third of the population has the specific gut bacteria that can metabolise the isoflavones (a type of phytoestrogen) in soy to a more potent phytoestrogen called equol. The amount of isoflavones needed daily to achieve therapeutic effects is contained in about 200g of tofu, or 100g of tempeh.

Phytoestrogen loaf

Why phytoestrogens may be beneficial for women

As well as their potential oestrogenic action, foods that contain phytoestrogens also offer other nutritional benefits including protein, fibre, vitamins and minerals. Soy protein may also help to lower LDL cholesterol (bad cholesterol).

Some studies have shown potential benefits of phytoestrogens in regard to cardiovascular risk, bone density and menopausal symptoms. About a third of women who eat a diet that delivers amounts of phytoestrogens typical of an Asian diet (particularly from soy foods) find that their menopausal symptoms improve. This is because only about one third (and possibly up to a half) of all people have the specific gut bacteria that converts soy isoflavone (phytoestrogen) diadzien, to the more potent form, equol.

High phytoestrogen foods

Different types of phytoestrogen include:

  • isoflavones (found in soy and other legumes such as chickpeas, mung beans and alfafa)
  • coumestans (found in alfalfa and clover sprouts, and sprouted legumes such as mung beans and soy sprouts)
  • lignans (found in linseed, grains and vegetables) 

Foods containing phytoestrogens

Soy products Grains Seeds and nuts Legumes
  • tempeh
  • soy beans
  • tofu
  • miso
  • whole soybean soy milk
  • soy drinks
  • oats
  • rice
  • barley
  • quinoa
  • rice bran
  • rye
  • wheat germ
  • flaxseed
  • sesame seeds
  • sunflower seeds
  • pistachios
  • almonds
  • chickpeas
  • lentils
  • red kidney beans
  • alfalfa
  • mung beans
  • split peas

soy millk and beansRemember, not all soy milks are fortified with calcium. If your brand does not have 120mg of calcium per 100ml or higher, a calcium supplement could be a good idea.

Eating a diet with moderate amounts of whole soy foods such as tofu, soy beans and breads made from soy flour is healthy; but avoid the highly processed soy foods and soy based supplements, as they work differently to soy that is found in nature.

Example of a phytoestrogen menu

This menu gives you ways to incorporate more phytoestrogen-rich foods in your daily meals. While you don't have to become a vegetarian, eating more phytoestrogens means preparing meals based more on plant foods and less on meat and chicken.

Breakfast

Baked beans on two slices of soy-linseed toast

Glass low-fat soy milk

Two slices of phytoestrogen loaf with cottage or ricotta cheese

Lunch

Soy linseed bread sandwich with salmon, cucumber and rocket

One cup of miso soup

Vegetable and soy bean soup

Dinner

Stir-fried noodles with Asian vegetables, tofu cubes and chicken

Tempeh burger and salad

Snacks

Choose two:

  • Three soy linseed crackers with ¼ cup hummus dip
  • Nut and seed bar
  • Soy smoothie with banana and 1-2 tablespoons wheat germ or ground flax seed
  • 1 slice of dark rye toast with spread and lentil dip
  • Miso soup
  • Apple and berry tofu muffin

Phytoestrogens as food & breast cancer risk

There has been much speculation about the risk of breast cancer from phytoestrogens in soy products. This is mainly based on the misconception that because these foods contain oestrogen-like compounds, they might stimulate breast tissue in the same way that our own body's oestrogen or pharmaceutical oestrogen can.

A 2006 review of research on the link between phytoestrogens and breast cancer showed that:

  • there is a small reduction in the risk of breast cancer associated with phytoestrogen consumption
  • the risk of breast cancer was reduced more in premenopausal women who consumed soy compared to postmenopausal women
  • a diet high in phytoestrogen in early life (before puberty) may be important for the anti-cancer effects of phytoestrogens in later life

There is conflicting data on the breast cancer risk of individual isoflavones, daidzein and genistein, that are found in soy. For this reason, supplements containing individual soy isoflavones, and soy supplements which have standardised amounts of these constituents should be avoided. Eating whole soy foods is safer.

A 2013 review highlights that studies that show that eating soy decreases the risk of developing breast cancer, are done in Asian rather than Western cultures. This is likely attributed to the greater amount of soy consumed in Asian diets compared to Western diets. In a typical Asian diet, the average daily intake of isoflavones is 25-50mg, whereas in Western diets the amount of soy isoflavones is less than 1mg per day! [3]

The bottom line with eating soy is that eating a diet with the amount of soy isoflavones typical of an Asian diet seems to be protective against breast cancer and it is these amounts that are needed for symptom relief.

How much soy contains 50mg of isoflavones?

50mg of soy isoflavones =

  • About 200g tofu
  • About 100-150g of tempeh
  • About three cups of whole bean soy milk
  • About 100g of cooked/canned soybeans

Phytoestrogen supplements are also available.

References

  1. Mourouti N, Panagiotakos DB. 2013) 'Soy food consumption and breast cancer.' Maturitas (, http://dx.doi.org/10.1016/j.maturitas.2013.07.006

  2. Messina, M. (2010). 'A Brief Historical Overview of the Past Two Decades of Soy and Isoflavones Research'. J Nutr 140(7):1350S-1354S

  3. Hilakivi-Clarke, L. Andrade, JE. Helferich, W. (2010). 'Is Soy Consumption Good or Bad for the Breast?' J Nutr 140(12):2326S-2334S 

  4. Trock BJ et al. (2006) 'Meta–analysis of soy intake and breast cancer risk'. J Natl Cancer Inst. 98(7): 459-471.

This web page is designed to be informative and educational. It is not intended to provide specific medical advice or replace advice from your health practitioner. The information above is based on current medical knowledge, evidence and practice as at February 2014.

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