What's wrong with Soya?
Soya - it’s a controversial story. While the health benefits of soya consumption have been shouted from the rooftops for many years now, there are also frequent reports that it may actually be bad for your health. The pro-soya view tells us that this wonder-food will reduce your risk of breast and prostate cancer, strengthen your bones, ease menopausal symptoms, prevent heart disease, is an excellent ‘hypoallergenic’ alternative to cow’s milk and a perfect protein source for vegetarians and vegans. On the other hand, we hear that Soya may actually contribute to the development of hormone-linked cancers of the breast and prostate, that it may suppress thyroid function, reduce fertility in men and affect the sexual and mental development of children. Also, that its allergic potential could be significant and serious.
So, what’s the truth? Let’s look at the facts.
Hormone Helper or Disruptor?
Claims have long been made that the phytoestrogens present in Soya have
hormone balancing properties. Phytoestrogens are naturally occurring oestrogen-like
‘chemicals’ estimated to be anywhere between 50 and 20,000
times weaker than natural oestrogen. If a woman is actually low in oestrogen,
such as during the menopause, the weak oestrogenic effect of phytoestrogens
can help to relieve menopausal symptoms. However, in cases of oestrogen
excess – which can occur as a result of taking the contraceptive
pill, HRT, from environmental exposure or simply from inadequate breakdown
of natural oestrogen – these weak phytoestrogens actually reduce
the oestrogenic effect by docking onto the oestrogen receptor sites, so
blocking the stronger oestrogens.
There have been a number of negative reports of the effects of Soya ‘isoflavones’
(the most active type of phytoestrogen) on fertility in animals, including
a case of tropical birds in New Zealand. The breeders began feeding their
birds a new Soya-based feed. The ensuing years saw decreased fertility,
early sexual maturation, deformed, stunted and stillborn chicks, aggressive
behavior and severe digestive problems. After changing to a non-Soya feed
all of these problems went away. Stories such as this have led people
to believe that Soya might be harmful to hormonal health. Dr Margaret
Ritchie, an expert in phyoestrogens at the University of St Andrews, is
quick to point out that different animal species metabolize isoflavones
differently. Even the rat, the animal used for most of the research trials
into Soya, handles Soya very differently from humans.
A recent report in The Observer’s Food Monthly magazine suggested
that eating Soya impaired human male fertility by affecting the sperm’s
ability to swim. However, the research this story was based on has never
been published in any scientific journal, so its validity is questionable.
And of the research that has been published, all shows that Soya does
not impair reproductive performance. This includes a study showing that
two months of Soya supplements had no effect whatsoever on semen quality
in men and several studies showing that ovulation occurs quite normally
in women using Soya products.
Another concern that has been raised is the effects of Soya-based infant
formula. At a recent conference on Soya in Belgium, Professor Thomas Badger,
from the Children’s Nutrition Centre at the University of Arkansas
for Medical Sciences, reported on a study that showed that babies fed
Soya-based formula do not develop any differently, either physically or
in terms of behavior, from babies fed standard formula. The study, which
involved 800 20-34 year old men and women who were either fed Soya based
formula or cow’s milk-based formula as babies, showed no difference
in 30 different aspects of reproductive health later in life.
As always, we at Physical Nutrition recommend breastfeeding wherever possible.
Phytoestrogens consumed in a mother's diet also appear in breast milk,
although the daily intake of breastfed babies remains negligible, even
when breast milk levels are increased as much as ten-fold by the mother's
use of Soya-based foods.
One study of babies in 1999 born to vegetarian mothers showed that baby
boys had a five-fold increased risk of hypospadias, a birth defect of
the penis. The study’s researchers suggested one possible reason
for this increased risk was higher exposure to phytoestrogens from Soya.
However, they warn that no conclusions can be drawn. So this remains a
theory, not a fact.
Cancer Protector?
Much of the support for Soya’s role in cancer protection comes
from epidemiological studies (population surveys). Certainly people in
Asia who eat Soya regularly have a much-reduced incidence of breast and
prostate cancer. But epidemiological surveys cannot be relied upon as
proof of cause and effect because of the many confounding factors that
always exist. In this example, for instance, the consumption of dairy
produce in these Asian nations is extremely low and we have seen increasing
evidence that high dairy consumption increases the risks of both breast
and prostate cancer. Also, the typical Asian diet is healthier than the
typical Western diet in many other respects – less red meat, more
fish and vegetables and so on.
Concerns have been raised about Soya food consumption actually increasing
the risk of breast cancer due to an oestrogenic effect. However, Soya
does not appear to have an oestrogen-like effect on breast tissue, suggesting
that it is highly unlikely to increase breast cancer risk. For example,
we can look at a study that compared consumption of Soya and density of
breast tissue measured by mammogram. Denser breast tissues known to be
a risk factor in developing breast cancer and the study showed that the
higher Soya consumers had less dense breast tissue than the low Soya consumers.6
In fact, use of Soya foods early in life, as well as later in life, has
consistently been shown to be protective against breast and prostate cancer.
One study has shown that Chinese women who had higher intakes of Soya
foods during adolescence had lower risk of breast cancer as adults. Several
studies have suggested that the use of Soya foods leads to a longer menstrual
cycle which may reduce risk of breast cancer, although not all studies
show an effect on menstrual cycle length. To date, there have been no
human studies which show an increased risk of cancer due linked to Soya
consumption and plenty that show protection.
Bad for Your Thyroid?
There has been long-standing concern over Soya consumption and thyroid health. Soya contains goitrogens, a natural substance that is also present in broccoli, kale, millet, peanuts, cabbage, pine nuts, turnips and Brussels sprouts. Goitrogens can block the uptake of iodine from the blood and iodine is essential for the health of the thyroid gland. By ensuring an iodine-rich diet, especially sea vegetables that are traditionally high in the Asian diet, any detrimental effects of Soya on thyroid function can be minimized. In clinical trials where Soya is added to people's diet, no harmful effects on thyroid function have been seen. One study has suggested that a diet containing higher levels of phytoestrogens is actually associated with a reduced risk of thyroid cancer in women. If you have an under active thyroid there is no need to rigidly avoid Soya. However, do ensure you have enough iodine in your diet from seafood. Iodine is also contained in some multivitamins.
Is Soya Highly Allergic?
Soya is often touted as an ideal alternative for people who have allergies
or intolerances to other food groups, particularly dairy products. Allergies
or intolerances are more likely to develop to foods that are a relatively
recent addition to our diet, and also to foods that we ‘over-consume’,
more so if digestive health is poor. Cow’s milk and gluten grains
such as wheat are common examples, especially if introduced in the first
four months of life before the gut and immune system are fully formed.
Soya might have been eaten regularly in Asia – since around 2000
BC – but it is still a relatively new food elsewhere, especially
in the West. If you eat any processed food at all, you are very likely
to be eating Soya since it is added to almost every food imaginable –
from bread to fish fingers, lasagna to ice-cream. York Nutritional Laboratories,
which conduct food allergy testing, found a 50% increase in Soya allergies
in 1998, the very year in which genetically-engineered beans were introduced
to the world market. York’s researchers noted that one of the 16
proteins in Soya beans most likely to cause allergic reactions was found
in concentrations of at least 30% higher in Monsanto’s genetically
modified (GM) Soya beans – another plausible explanation for the
increasing rate of allergy to Soya. Another possible explanation is early
feeding of Soya to non-breastfed babies who have, perhaps, become allergic
to dairy formulas. No food, other than breast milk, is allergically safe
in the first four
months of life. Most allergy testing laboratories find Soya within their
top ten to fifteen most common allergenic foods. Since, peanuts and Soya
beans are members of the same botanical family (the grain-legume type)
people allergic to one are often allergic to the other.
Not All Soya is the Same
There is a difference between whole Soya beans and soy protein isolates (isolated compounds of Soya). Soya protein isolates are processed out of Soya beans. The fibre from the Soya beans is removed with an alkaline solution and then the beans are put into an aluminum tank with an acid wash where they may absorb some aluminum. The ‘food’, which no longer resembles the original Soya bean, can then be made into anything, including textured vegetable protein (with added chemical flavours), flavour enhancers in soups and sauces (as hydrolysed vegetable protein), ‘bacon rashers’ and added to many processed foods. This is an important difference between tradition Asian and Western-style Soya foods. Asian Soya foods that are made from traditional processes, such as fermentation and precipitation, have been part of the Asian diet for thousands of years, so in effect they are tried and tested. These include Soya sauce, tamari, miso, natto, tempeh, tofu and soya milk. Industrially-created Soya isolates have really only been a part of our Western diet for a few decades at most.
Conclusions and Recommendations
Is Soya safe? Recently a group of scientists from several different countries looked at more than 200 studies on Soya safety and concluded that: “the available scientific evidence supports the safety of isoflavones as typically consumed in diets based on Soya, or containing Soya products”.
Is Soya good for you? It would certainly appear that there is a large amount of research supporting Soya’s health benefits and that, for the most part; the negative Soya stories are based on bad science.
How much Soya should you eat? In Japan, where Soya is a regular part of the diet, the average daily consumption is approximately 65g per person,which provides an approximate isoflavone (the most active phytoestrogen) intake of 20-50mg. Higher Soya intakes have been reported in China and Singapore, where daily isoflavone intake is 65.9mg and 61.4mg, respectively. Phytoestrogen expert Dr Ritchie believes that we should eat a small amount of Soya daily, as blood levels of the beneficial compounds start to decline six hours after consuming.
Based on Dr Richie’s research, the recommendation is that you aim for around 15mg of phytoestrogens a day. This is easily achieved by having a small portion of tofu (100g serving provides 78mg), or a 100mg glass of Soya milk (11mg) and a portion of chickpeas, perhaps as hummus (2mg). Eating rye bread, bean sprouts, beans, lentils, nuts and seeds also helps boost your levels – these are the very foods that are staples in the East and unheard of by many in the West.
While most research focuses on the isoflavone class of phytoestrogen, which is particularly rich in Soya, there are other classes of phytoestrogens which also contain cancer-protecting properties.
These include:
- Lignans - rich in linseeds, black/green tea, coffee, fruits and vegetables, split peas, lentils and beans
- Flavones - rich in fruits, nuts, green vegetables.
- Coumarins – in cabbage, peas and liquorice
- Acyclics – in hops (Belgium beer is the richest source of acyclics)
- Triterpenoids – in liquorice and hops
- Coumestans – found in alfalfa, beans, split peas and lentils.
Reproduced form Patrick Holford.com
