Soy: Healthy or Toxic?
Soy: Healthy or Toxic?
Controversy abounds over soy. Beneficial effects have been reported in relation to heart disease, breast cancer, prostate cancer, menopausal symptoms, thyroid function, bone health and even cognitive function. Yet conversely media reports and numerous websites claim exactly the opposite. Frightening headlines touting “the truth about soy” allege soy is toxic to humans and causes numerous detrimental health outcomes including reproductive problems, an increased risk of breast and prostate cancers, decreased immune function, gut problems, and in children early menarche and feminisation of boys. It’s enough to turn you off your soy latte for life. But who do we believe?

Soy is a legume that is fairly unique in the plant kingdom, in that it provides all of the essential amino acids (the building blocks of protein) that humans need. In contrast almost all other plant foods are missing or low in one or more of these amino acids, meaning that vegetarians must consume a variety of plant foods to meet their protein requirements. For this reason soy beans, tofu, tempeh, soy drink and other soy foods have long been a mainstay of vegetarian and vegan diets.

But on the whole soy foods have not played a major role in the typical Western diet. In contrast, soy is regularly consumed by many Asians at all stages of life from weaning to old age. This difference in levels of soy consumption is what got the ball rolling in soy research. Scientists found that levels of heart disease and many cancers, including breast cancer, were far lower in these soy-eating Asian countries, compared to levels in the West. Numerous studies followed to try to identify what it was about soy that might be protective.

Research has centred on two aspects of soy – soy protein and compounds found in soy called isoflavones. Isoflavones are phytoestrogens (meaning ‘plant oestrogen’) and are similar in structure to the hormone oestrogen. These phytoestrogens can act in two ways:

  • They can act like oestrogen. This may be beneficial during menopause for example, when natural oestrogen levels are dropping. Theoretically consuming sufficient phytoestrogens-rich soy at this time can reduce menopausal symptoms.
  • They can block the action of oestrogen. This is potentially beneficial in for example breast tissue where oestrogen stimulates growth of both normal and cancerous cells. At least one of the isoflavones in soy, called genistein, has been shown in animal studies to inhibit the development of breast cancer.

Additionally, isoflavones have been shown to be powerful antioxidants and may in this way contribute to protection against diseases including cancer and heart disease.

However before we go into the different areas of research there is another key problem with soy in the West. Soy is a cheap source of protein and therefore it is used ubiquitously in the food industry. More worryingly to me is that it's rife in so-called fitness and health products. Try reading the ingredients list of many high protein, low carb bars, balls and shakes and you'll find 'soy protein isolate' high on the list. This is extracted, refined protein from the soy bean. This is not a wholefood and furthermore may come from genetically modified soy - makes up the majority of soy grown in the USA.

Soy & heart disease

In 1995 a report was published in the prestigious New England Journal of Medicine that concluded (on the basis of 38 controlled clinical trials) that soy protein significantly reduced blood cholesterol levels, particularly LDL (‘bad’) cholesterol, and triglycerides (another blood fat linked to an increased risk of heart disease).  On the back of this report the U.S. Food and Drug Administration now allows food manufacturers to claim on the labels of low-fat foods containing at least 6.25g of soy protein that soy can help reduce the risk of heart disease.

Many other countries, including the UK, have followed suit but as yet Food Standards Australia and New Zealand (FSANZ) have not approved such a claim here and it is unlikely that they will. A more recent review of the evidence published in the journal ‘Circulation’, suggests that this claim is rather premature. It concludes that soy protein has only a very small effect on LDL-cholesterol, reducing it by a meager 3% or so, while having no effect on triglycerides or ‘good’ cholesterol. Furthermore the studies showing a beneficial reduction in cholesterol used large quantities of soy - ~50g a day. In reality this equates to drinking about 7 cups of soy drink or close to 600g of tofu – every day! You would have to be pretty dedicated to keep up this level of intake.

Nevertheless, the authors did recognise that consuming soy foods in place of animal foods (high in saturated fat and cholesterol) should benefit heart and overall health since soy foods are low in saturated fat, a source of healthy unsaturated fats, and rich in fibre and other nutrients. All this research is really telling us that having soy drink instead of milk and the odd tofu burger is not enough to bring down your cholesterol levels. But, choose the tofu burger over a regular burger, and replace the fattier cuts of meat in your diet with tofu or tempeh, and your heart will be thankful.

Soy & Cancer

Some of the early studies comparing cancer rates across countries showed a benefit of soy consumption, and many soy and health food companies leapt on the results. However the picture is far from clear and a few worrying reports have emerged suggesting that concentrated soy supplements in fact stimulated cancer growth in subjects with existing breast cancer.  Of course this so often happens in nutrition research – scientists think they have isolated the important component of a food and try giving it as a supplement and low and behold the effects are not the same. Try as we might a good diet just cannot be packaged in a pill.

The Cancer Council has issued a position statement to help clarify the research information we have on soy and give the best advice possible to consumers. They state that:
  • a high consumption of soy foods may lower the risk of breast and prostate cancer, but only by a little;
  • there is no association between soy foods and the risk of any other cancers;
  • while they may have a protective effect, there is also some evidence that phytoestrogens might stimulate the growth of existing hormone dependent cancers (ie the risk is if you already have hormone-dependent breast cancer and consume a lot of soy)

They therefore recommend that soy foods be included in a healthy high plant food diet, but that soy or isoflavone (the isolated phytoestrogens) supplements should not be used to prevent cancer or be used by cancer survivors. Furthermore if you have or have had breast cancer, they recommend you do not consume a large amount of soy food. For more information click here to visit The Cancer Council website.

Soy and Menopause

Many women have sworn that eating more soy foods during the menopausal years has helped to reduce symptoms such as hot flashes and mood swings. However the vast majority of studies have failed to confirm these anecdotal findings. Yet it is interesting to note that the reported incidence of hot flashes differs across countries with varying soy intakes. For example while 70-80% of European women report hot flashes, only 18% and 14% do so in China and Singapore respectively. These differences are perhaps due to the way in which soy is consumed – not as supplements but as key foods in an overall healthy diet.

Soy & Reproductive Health

Reports of girls starting menarche at an increasingly young age and the feminization of our boys and men are among the more horrific of the claims made against soy. The basis for this is legitimate enough – that if infants are fed soy formula and young children consuming soy in an increasing number of foods they are exposed to the effect of an oestrogen-like substance for a far longer period of time. Certainly infants in Asia are rarely given soy formula, but they are fed many soy foods from the age of weaning. These children have no ill effects on their reproductive systems and there seems little concern from soy foods.

With respect to soy infant formula, a major study published in 2001 in the Journal of the American Medical Association, followed more than 800 men and women fed soy formula as infants into adult life. They found no significant differences between this group and those fed a cows’ milk formula, including any effects on the reproductive system. That said there are those who seem to believe soy formula is healthier and there is simply no basis for this.

The bottom line is breast-feeding infants has indisputable advantages to bottle feeding, but modified cows’ milk formulas are a safe and effective alternative. Soy-based formulas were developed for use in infants allergic or intolerant to cows’ milk and therefore only consider using them if advised to do so by your doctor or health professional.

The Soy Bottom Line

While there seems little evidence to support the alarmist claims of the anti-soy network, neither is there compelling evidence that soy is quite the health food some have cracked it up to be. The traditional Asian diet, rich in soy foods, has been shown to be a healthy diet that undoubtedly plays a role in their low rates of several chronic diseases including heart disease, obesity and certain cancers. What they don’t do is take concentrated soy or isoflavone supplements, nor do they consume a plethora of processed, packaged food marketed as healthy just because it is made from soy, alongside a diet too high in saturated fat, processed foods and so on typical of many Westerners.

Traditional soy foods such as tofu, soy drinks made from whole soybeans, tempeh and whole soy beans are healthy additions to your diet, particularly if they replace processed and fatty meats. But there appears to be nothing to be gained, and potentially much to lose, from packaging soy in a pill or wolfing down refined extracts of soy in a bar promising to help you to burn fat. It's another example of why whole foods matter.