The ideal diet

The ideal diet is high in fibre, vegetables, fish protein, unprocessed cereals and grains, and mono-unsaturated fat rather than saturated (animal) fat.

'Colourful' fruit and vegetables are the most nutritious in terms of vitamins and minerals. High fibre diets protect against high cholesterol, heart disease, colon cancer and possibly other cancers. 

Fish contains omega-3 fatty acids, which can reduce blood fats and blood clotting, and fish bones (for example in sardines and tinned salmon) are a rich source of calcium.

What are phytoestrogens?

Phytoestrogens are compounds that occur naturally in plants (phyto) and which, under certain circumstances, show some of the same activities as the female hormone oestrogen. Phytoestrogens are much weaker than human oestrogen, and their effects are different from those of hormones found in Hormone Therapy (HT).

When eaten, phytoestrogens bind to oestrogen receptors (also called estrogen modulators or ERs) and can promote 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 (the oestrogen environment), how the phytoestrogens bind to ERs and particularly which ERs they bind to.

Our own body’s oestrogen can bind to either (o)estrogen receptor alpha (ER-α) or (o)estrogen receptor beta (ER-β) with equal ability. When oestrogen binds to ER-α, it stimulates growth of hormone-sensitive tissue. For example, the processes involved in the normal menstrual cycle are activated by oestrogen binding to ER-α. ER-α is also involved in the growth of hormone-sensitive tumours such as breast cancer, endometrial cancer and prostate cancer. ER-β has different functions from ER-α and seems to counteract processes triggered by ER-α.

Phytoestrogens have a similar chemical structure to our own body’s oestrogen, so can also bind to ER-α and ER-β. Isoflavones, a type of phytoestrogen found in legumes such as soy and red clover, bind to ER-β more readily than to ER-α. For this reason, isoflavones are sometimes classified as selective (o)estrogen receptor modulators (SERMs).

As mentioned above, phytoestrogens can act as an oestrogen or anti-oestrogen depending on the oestrogen environment. For example, in a perimenopausal woman where the body’s own overall oestrogen level is low, phytoestrogens may reduce hot flushes by binding to and activating ER-β (an oestrogenic effect). Conversely, in a younger woman, these phytoestrogens may act as an ‘anti-oestrogen’ by activating ER-β and counteracting the effects of the body’s natural oestrogen.

Phytoestrogens and health

Eating a phytoestrogen-rich diet has been linked to reduced rates of heart disease and of some cancers. However, populations that have a high phytoestrogen intake also consume predominantly fruit and vegetables and only a little animal fat. It is not yet known whether the lower disease rate in these communities is due to overall healthier diet and lifestyle, or is linked to the specific effects of phytoestrogens. Furthermore, plants that contain phytoestrogens possess a variety of non-hormonal properties that play a role in cancer and disease prevention.

The best known types of phytoestrogen are:

• isoflavones (found in red clover, soy and other legumes)
• coumestans (found in alfalfa and clover sprouts)
• lignans (found in linseed, grains and vegetables) 

It is essential to make the distinction between nutrients consumed in food and nutrients in supplements taken as powders or pills. We need to understand that the latter are not "natural" therapy, but rather pharmacotherapy (drug therapy), which can have adverse effects and should be evaluated with the same rigor as conventional pharmaceuticals. Taking phytoestrogen supplements as isolated soy protein concentrates or in tablet form should not be encouraged at this stage.

Furthermore, there is conflicting evidence as to whether phytoestrogen supplements are more effective than placebos for relieving menopausal symptoms. Of specific concern is the use of phytoestrogen supplements in women who have had breast cancer, and potential interference with the therapeutic effects of tamoxifen. Soy supplements are therefore not recommended for women with breast cancer or a history of breast cancer (see below).

There is also some promising (but less convincing) data that phytoestrogens may improve cognition.

Heart disease

Consuming a diet high in soy may lower total and LDL cholesterol in men and women. Animal studies also indicate that components of soy protein may have beneficial effects on blood vessel function. The observed benefits are greater for natural soy protein (tofu or soy flour) than for the extracted phytoestrogens alone. A diet referred to as the Portfolio Diet, which Canadian researchers have demonstrated can reduce LDL-cholesterol (“bad cholesterol”) as significantly as a standard statin drug therapy, includes 50g of soy protein daily (the other components being high levels of viscous fibre, 2g of phytosterols and 30 g of almonds per day).

Cancer

There is some evidence to suggest that phytoestrogens may protect against cancer of the breast and uterus. The anticancer effects appear to be because phytoestrogens protect against the growth enhancing effect of our own body’s oestrogen in these hormone-sensitive tissues. Again this is due to activation of ER–β, which protects the tissues from the excessive oestrogenic effects Phytoestrogens also have anticancer effects unrelated to their oestrogenic actions, which appear to be important. Additionally, soy isoflavones can act as antioxidants, which may contribute to their anti-cancer properties.

Breast cancer

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

In 2006 a study was published that examined all of the research on phytoestrogens and breast cancer between 1978 and 2004. (Trock, BJ et al 2006. ‘Meta-Analysis of Soy Intake and Breast Cancer Risk’ J of the National Cancer Institute 98 (7), pp 459-471). There were a number of important findings to come out of this analysis. Firstly, it was shown 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. It has also been shown that a diet high in phytoestrogen in early life (before puberty) may be important for the anti-cancer effects of phytoestrogens in later life.

Secondly, there is conflicting data on the individual isoflavones found in soy, depending on the doses used. Some studies have shown a stimulation of human breast cells, others have shown a prevention of stimulation. It is important to consider that test tube studies of compounds isolated from foods do not fully represent what occurs in the body when a food containing differing amounts of complex compounds is eaten. It is generally agreed that, while test tube evaluation of compounds provides important information, there are more suitable methods of assessing safety when evaluating food products.

Thirdly, and most importantly, it is suggested that highly processed soy supplements such as soy protein isolate, isoflavone-rich soy extracts or isoflavone capsules act differently to foods made from soybeans or soy flour. The authors of this review concluded that it is not recommended for women at high risk of breast cancer or breast cancer survivors to take these highly processed soy supplements, such as soy protein isolate, isoflavone-rich soy extracts or isoflavone capsules.

There is no evidence to suggest that eating a diet of soy foods in amounts consistent with Asian diet is detrimental to breast health. This finding was again confirmed in a review published in Nutrition Journal in 2008, which stated that there is no evidence that isoflavone intake increases breast cell proliferation (growth) in pre- or postmenopausal women, with or without a history of breast cancer, and that eating phytoestrogens at levels consistent with historical Asian soy food does not result in adverse stimulation of breast tissue.

In summary, it is appears that eating a diet with moderate amounts of whole soy foods such as tofu, soy beans, and breads made from soy flour is healthy; but you should probably avoid the highly processed soy based supplements, as they work differently to the way soy exists in nature.

Women's health

When phytoestrogens act as oestrogens they are much weaker than the oestrogen produced in humans. The outcomes of studies examining the effects of soy foods in alleviating hot flushes have varied.

Taking 25 g (two heaped dessertspoons) of linseeds or flaxseeds each day has been shown to reduce vaginal dryness. These seeds can be sprinkled on breakfast cereals or added to smoothies. Linseeds are also a good source of oils that we cannot make in our body (essential fatty acids). When seeds are ground, these good oils are lost over time (oxidised), so that two weeks after grinding the oils are completely destroyed. To avoid the loss of these good oils, freshly grind the amount of seeds that would be eaten within two weeks (in a food processor, with the nut grinding attachment of a blender or in an electric coffee grinder) and store in an airtight container in a fridge.

General health

Multiple lifestyle factors, including the food we eat, are related to good health and protect against disease. Improving diet at any stage of life will result in health benefits. As well as their oestrogenic action, foods that contain phytoestrogens also offer other nutritional benefits including protein, fibre, vitamins and minerals.

Food sources

Legumes (particularly soybeans), wholegrain cereals and seeds contain high levels of phytoestrogens. Consumption of dietary isoflavones is higher in Japan, China and some other Asian countries and considerably lower in Western countries. Traditional Asian foods made from soybeans include tofu, tempeh, miso and edamame (fresh soybeans harvested and eaten while still green). Research into the phytoestrogen content of Australian food is ongoing.

Phytoestrogen content varies between foods, even within the same group of foods. For example, the phytoestrogen content of soy beverages varies depending on processing and the type of soy bean used.

There are a variety of soy products now readily available. Look for soy milk that contains all parts of the soy bean, rather than ‘soy isolates’ or ‘soy protein isolates’, and choose calcium enriched soy milk for your bone health.

How much each day?

There is considerable variation between women in how dietary phytoestrogens, particularly soy, can benefit them. This is due to the presence or absence of bacteria in the gut that can covert isoflavones into stronger compounds.

Soy foods are not a regular part of the Australian diet. We need to make changes to the way we eat to get the benefits of these foods. Try to eat a wide variety of plant foods every day, including at least one of the following every day:

• 2-4 slices soy and linseed bread, or multigrain bread (for lignans)
• 1-2 cups soy milk (low fat, calcium enriched)
• 150 grams tofu
• 30-40g linseed
• 1 cup soy beans or other legumes

How to include these foods in your diet 

• Replace some meat meals with cooked dried beans
• Use legumes in soups and casseroles
• Add linseed to breakfast cereal , smoothies or yoghurt
• Make a fruit smoothie with soy milk, or with half soy and half cow's milk
• Add firm tofu to stir fries
• Make your own muesli with rolled oats, wheatgerm, linseed, sesame seeds, dried fruit and nuts
• Eat bread made with soy flour
• Instead of just wheat flour in baking, use half wheat flour and half soy flour
• Add sprouts to salads and sandwiches

Summary

• Phytoestrogens are plant derived compounds with oestrogen-like activity
• Phytoestrogen containing foods such as soy, whole grains and seeds are healthy food choices containing vegetable protein, fibre and nutrients
• Phytoestrogens bind to oestrogen receptors in the human body, mimicking the effects of oestrogen in some tissues and opposing it in others (depending on which receptors are bound)
• There is considerable variation between individuals in how phytoestrogens are absorbed and metabolized
• Soy-containing vegetable proteins and phytoestrogens may reduce the risk of heart disease and lower cholesterol levels in men and women
• Phytoestrogens may have a possible role in osteoporosis prevention and improved cognition, but more research is needed
• The evidence on phytoestrogens improving menopausal hot flushes varies
• Phytoestrogens consumed in whole food in amounts consistent with an Asian diet do not appear to be detrimental to breast health
• It is not recommended for women at high risk for breast cancer or breast cancer survivors to take highly processed soy supplements such as soy protein isolate, isoflavone-rich soy extracts or isoflavone capsules

Further resources

Books

Nutrition for Life
by Catherine Saxelby

Recipes For a Great Life: Simple steps to wellbeing and vitality
by Gabriel Gate & Dr Rob Moodie

Zest - over 120 recipes
by Catherine Saxelby & Jennene Plummer

Fact Sheets

Healthy Eating 63.82 Kb

Healthy Eating (6.8 MB)

Nutritional Tips 106.39 Kb

Nutrition for Women at Midlife (6.34 MB)

Websites

Nutrition Australia - www.nutritionaustralia.org

Content updated June 23, 2011