Is soy really good for you?

Long dismissed as only fit for hippies and vegetarians, soy has become one of the most controversial foods. Today, if you google “soy”, among the millions of results will be articles declaring soy a wonderfood, along with claims it’s a poison responsible for most of the health problems in Western society.

Mixed messages from public health bodies have made the situation worse. Even the cancer groups can’t agree on the benefits or otherwise of soy, and in 2007 one group even released two contradictory press releases on the same day 1. The first discouraged breast cancer sufferers from eating soy, while the second claimed soy foods were part of a diet that could lower the risk of cancer.

Then what is the truth about soy? Is it a superfood that you should include in your diet on a regular basis or is it, as one website says, “the next asbestos”?


What is soy?

The soybean is a legume, meaning it grows in pods much like peas, broadbeans and chickpeas. While they’re native to East Asia, they’re now grown in many countries. Soybeans are mainly known as a food for humans, though the vast majority of the world’s soy crop is not turned into tofu but is instead converted into oil, fed to cattle and used as a biofuel.

Fresh soybeans are usually sold as edamame beans and you can buy them both in the pod, podded or frozen. Dried soybeans are also available and these need to be soaked and cooked before use. Soy is also made into a range of different products, including tofu, soymilk, soy flour, soy meal, tempeh, textured vegetable protein (TVP), soy lecithin, soy sauce and soybean oil.

Soybeans are highly nutritious and prized by vegetarians for their high protein content. They also contain a lot of fibre and have a low GI and a whole range of nutrients, antioxidants and phytochemicals that contribute to their healthy image.

Soy has also been linked with reducing heart disease and cancer risk and prolonging lifespan. Women have been encouraged to eat soy foods regularly to reduce not only the symptoms of menopause, but also breast cancer risk and the likelihood of osteoporosis. Men have also been targeted, particularly by soymilk manufacturers, with claims it can reduce prostate cancer risk.


Soy’s tarnished image

Though it was once the food of only extreme health nuts, in the 1990s medical studies continually showed the positive effects of soy and it began to gain media and public attention. In 1999, Time magazine lauded the health benefits of the bean in an article titled ‘The Joy of Soy’. Soy had hit the mainstream and become a superfood.

Food manufacturers started churning out new products. Soy was no longer confined to tofu, tempeh and soymilk, but became an ingredient in vegetarian sausages, burgers, yoghurt and mock-meat foods. Cafes started stocking soymilk for use in coffee and milkshakes, and if you browse the frozen food section of the supermarket, soy is now found in an amazing collection of different foods. In the US, soybean oil is fed to cattle and is one of the fats of choice in fast food cooking. Without most of us realising it, soy has become a regular part of our diets.

In recent years, though, soy’s image has been somewhat tarnished, particularly on the internet. Articles on soy charge the bean with a whole range of crimes, from increasing the risk of breast cancer to causing brain damage, encouraging developmental abnormalities in children and even “making kids gay”. The bean has gone from being regarded as a healthfood to being considered by many as a nutritional pariah.


The charges against soy

The negative press against soy makes the following claims:

  • Soy contains anti-nutrients, substances that prevent us from digesting protein and block the uptake of essential nutrients, inhibiting thyroid activity and leaving us at risk of deficiencies and disease.
  • Soy does not protect against heart disease.
  • Rather than preventing cancer, soy actually increases the risk of breast and prostate cancers.
  • Soy causes birth defects.
  • Infant soy formulas are bad for babies.

These are serious charges and, if true, would mean soy was a food that should be avoided by all. When you delve into the soy story, however, it becomes clear there is an element of hysteria on both sides. Soy is both over-maligned and also over-hyped. While the more extreme claims about the health benefits of soy are not entirely true, neither are the wilder claims of the soy detractors.



One of the main charges against soy is that it contains anti-nutrients. Goitrogens block the uptake of iodine, which affects the thyroid. At the same time, enzyme inhibitors derange protein digestion and phytates prevent the absorption of a range of minerals, including zinc, magnesium and iron. This raises concerns that eating soy foods will cause both protein and mineral deficiencies, leaving people prone to disease and ill-health.

It is true that soybeans contain all these substances. Raw soybeans contain goitrogens, phytates and other substances that, between them, block the use of iodine, vitamin B12, vitamin D and a range of other nutrients. Eating large amounts of raw soybeans would leave you at risk of protein deficiency, pernicious anaemia, rickets and so on.

However, we don’t eat soybeans raw. We eat them cooked or processed in tofu, tempeh and soymilk. Anti-nutrients are destroyed by these cooking and processing methods. Boiling water dissolves some compounds, heat denatures the protein-based anti-nutrients, while others oxidise into harmless compounds.

Moreover, soy is not the only food to contain these substances. Pine nuts, broccoli, cauliflower, cabbage, strawberries and peaches all contain goitrogens, while phytates are found in other legumes as well as grains, nuts and seeds. To avoid these compounds, we’d have to avoid some of the healthiest foods around.


Does soy protect against heart disease?

One of the earliest claims for soy was that it protected against heart disease, by lowering LDL cholesterol and triglycerides, two benchmarks for cardiovascular risk. Indeed, in 1999, the US Food and Drug Administration allowed companies to put on the packaging of soy-containing foods a health claim that the product “may reduce the risk of heart disease”.

In 1995, an analysis of 38 controlled clinical trials, published in the New England Journal of Medicine, found soy protein significantly decreased total cholesterol, LDLs and triglycerides. However, further studies since then have been more circumspect and a 2006 review of information by the American Heart Association found that replacing dairy and animal protein with 50g of soy per day reduced LDL cholesterol levels by about 3 per cent.

It seems that soy does reduce your risk of cardiovascular disease, although the effect is small. However, the American Heart Association has continued to recommend small amounts of soy foods be included regularly in the daily diet because of this effect and also “because of their high content of polyunsaturated fats, fibre, vitamins and minerals and low content of saturated fat”. These nutrients are beneficial for reducing overall cardiovascular risk and improving health in general.


Soy and cancer

When soy first started gaining prominence in the late 1990s, part of the reason was its believed role in protecting against cancers, particularly breast cancer. However, some of soy’s most strident critics now claim the bean not only fails to prevent cancer but can actually increase the risk.

The idea of soy reducing breast cancer risk came from population studies that revealed a very low rate of both breast and endometrial cancer in Asian countries, where soy was consumed on a regular basis. It was believed compounds in soy, called phyto-oestrogens, protected women from these cancers. Phyto-oestrogens are plant chemicals that are structurally similar to the hormone oestrogen, produced by all women.

The theory around soy and breast cancer stated these compounds exerted a weak oestrogenic effect in the body, which helped protect against the more potent oestrogens involved in some breast and endometrial cancers. Therefore increasing your consumption of soy would mean more phyto-oestrogens in your diet and increased cancer protection.

It’s not just women who supposedly benefit from regular soy consumption. Large population studies in the US have found daily consumption of soymilk by men could reduce the risk of prostate cancer by up to 70 per cent.

However, further studies have been somewhat inconsistent and there’s still a lot about this area we don’t know. Some researchers have suggested it’s eating soy in childhood and adolescence that’s important. There is also concern that the slight oestrogenic effect of soy, instead of protecting, may actually stimulate the group of cancers that respond to hormones. There is disagreement among cancer researchers on this topic and, as mentioned, there are even discrepancies in the advice given to cancer sufferers by different cancer bodies.

Large-scale studies are currently underway and these will yield more information on soy and cancer risk. However, in the meantime, the balance of evidence indicates, for most people, small and regular amounts of soy are beneficial. The current Cancer Council recommendations state:

“From the current evidence, it is believed that a moderate consumption of soy foods (eg 1-2 serves of soy foods/day) along with an overall healthy eating plan is unlikely to have adverse effects. This is consistent with The Cancer Council’s recommendations and dietary guidelines to eat a diet rich in plant foods.”

However, there is enough concern to recommend that people with hormonally responsive tumours and those taking the drug tamoxifen should reduce their soy intake. This doesn’t mean total avoidance but limiting your intake to three or four servings a week.


Is soy safe for children?

One of the most frightening accusations against soy you’ll find online is that it may cause birth defects. This seems to be mainly based on a 2000 study that suggested an increase in hypospadias in baby boys born to vegetarian mothers. Hypospadias is one of the most common congenital abnormalities, involving malformation of the penis, and is correctable by surgery.

However, while this study looked at 7928 baby boys, there were only 51 cases of hypospadias. Of the vegetarian mothers, only seven had babies with this condition, which is not enough to prove the link. A later study looking at both maternal and paternal risk factors found no link between the mother’s diet and hypospadias. Instead, stronger risks came from parents who smoked, mothers who had poorer general health and low birthweight in the baby. Soy consumption has not been linked to any other birth defects.

Soy formulas have also been accused of being “birth control for babies”, as the phyto-oestrogens exert an oestrogen effect on the baby. While I’d question the extremity of this claim, there is a concern that large quantities of soy may affect the development of infants. It is possible that the same phyto-oestrogens that help the health of adults may have a very different effect in babies.

Milk is babies’ primary source of nutrition, so soymilk formulas would give them a relative daily dose of soy that far outweighs what an adult would consume. However, at the moment, most research has failed to show any difference in the sexual maturation of children who were fed soy formulas at birth.


Soy recommendations

Soy foods have many nutritional benefits and are a good food to include in your diet. However, reducing your risk of cardiovascular disease and cancer is not about consuming one food. Rather, it’s about eating a diverse and wide-ranging diet that may include soy but also includes plenty of vegetables, fruit, wholegrains, mono- and poly-unsaturated fats and regular protein.

While soy is not a dangerous food, problems arise when we view it as a nutritional magic-bullet. As stated above, much of the evidence for soy protecting against cancer is based on population studies, particularly in Japan where soy, in the form of tofu, tempeh, miso and natto, is a regular part of the diet. However, it’s eaten in moderate quantities as part of an overall diet that includes fish, vegetables and rice and is therefore low in saturated fatas well as high in vitamins, minerals and antioxidants.

Viewing soy as a superfood and magic cure has also led to its inclusion as an additive in a huge range of foods. While soybeans may have health benefits, these foods contain soy that’s been extracted, highly processed, flavoured and coloured. This is not how people have eaten soy in the past. Instead, the safe history of regular soy use has been about eating foods made from the whole bean. Tofu, tempeh, miso, soymilk and natto are all proven foods.


Suggestions for how to use soy

For soy beginners it can be hard to know what to do with foods like tofu and tempeh. One of the easiest ways of increasing your consumption of soy is to request it in dishes when eating Thai and Vietnamese, or have some miso soup when eating Japanese food. If you’re serious about increasing your consumption, though, it’s worthwhile experimenting with soy at home.

Soy options

  • Choose either organic or non-genetically modified soy products.
  • Different tofus have different flavours and texture. For stirfries, choose firm tofu and experiment with a few different brands.
  • Miso paste can be added to soups and casseroles.
  • In summer, slivers of tofu and tempeh can be added to ricepaper rolls.
  • Saute cubes of firm tofu with sesame seeds and serve with lots of green vegies for a quick and nutrition-charged dinner.
  • lice up tempeh and add to salads, sandwiches and wraps with avocado and handfuls of salad.
  • dd a teaspoon of miso to a homemade salad dressing instead of using salt.

Kathryn Elliott is a nutritionist and herbalist with more than four years clinical experience. She practises at the Source of Wellness in Gladesville, Sydney. Kathryn also writes a professional blog, Limes & Lycopene, which includes articles, recipes and healthy diet advice.

The WellBeing Team

The WellBeing Team

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