For the last decade the humble soya (soy) bean has alternately been portrayed as a hero and a villain. In Asia the prevalence of soy products in the traditional diet has been earmarked as the saviour of menopause and a strengthener of bones. In recent times there appears to be a dedicated campaign to show this food is a trigger of oestrogen dependent cancers, feminisation of boys and many other undesirable conditions.
It’s time to untangle the evidence for and against soy, and make some sense of why the sides are so divergent.
The Asian diet
Soy in the form of tofu, tempeh, miso, ‘milk’ or the cooked fresh or dried beans is a cornerstone of most Asian diets. Generally it is eaten regularly in small amounts. For example in Japan, a small bowl of miso, green soy pods (edamame), a splash of salty soya sauce or a handful of tofu cubes might be eaten most days. A traditional diet featuring soy in this way, also low or non-existent in dairy foods, has been associated with strong bones and not attracted any of the negative health connotations that have appeared in the West.
So if a small amount of soy is good for us, what about a large amount?
In the West serving sizes are markedly larger. Instead of tofu cubes, a large ‘steak’ may replace meat in a meal. Soy milk, instead of just the straight bean extracted in water, is turned into a sweeter, oily drink and drunk by the litre. In the name of being healthy, we have ‘supersized’ a super food.
What is more soy has entered the food chain increasingly as a food for livestock and as a ‘filler’ or bulking agent in some processed foods, meaning we are getting concentrated soy hits when we least expect it.
More than 60% of all processed food in Britain today contains soya in some form, according to food industry estimates. It is in breakfast cereals, cereal bars and biscuits, cheeses, cakes, dairy desserts, gravies, noodles, pastries, soups, sausage casings, sauces and sandwich spreads. Soya, crushed, separated and refined into its different parts, can appear on food labels as soya flour, hydrolysed vegetable protein, soy protein isolate, protein concentrate, textured vegetable protein, vegetable oil (simple, fully, or partially hydrogenated), plant sterols, or the emulsifier lecithin. Its many guises hint at its value to manufacturers.
Soya increases the protein content of processed meat products. It replaces them altogether in vegetarian foods. It stops industrial breads shrinking. It makes cakes hold on to their water. It helps manufacturers mix water into oil.
from The Guardian
Furthermore, as soy’s fame has spread – especially in it’s role as a phytooestrogen as a beneficial treatment for the symptoms of menopause, soy in a high dose, concentrated supplement form has been added to some people’s health regimes.
As awareness of issues with dairy products have spread, with more people discovering they are intolerant or allergic to this highly used food, soy often in large amounts of milk or pseudo-dairy such yoghurt, cheese or icecream has gained popularity. The humble bean has gone a long way.
But is soy really good for us?
In the last few years there has been some minor studies associating various soy derivatives with brain shrinkage (the Hawaiian geriatric study looking at tofu eaters, now considered to be unconvincing even by the anti-soy camp), feminisation of young boys (soy formula), thyroid conditions, infertility and even cancer.
At the same time studies continue to show positive health benefits of eating soy based foods such as helping prevent breast, prostate and possibly bowel cancer.
How can this be so?
Popular theories to explain these divergent viewpoints include: type and quantity of soy food in the diet, biased studies, broad hypotheses (if soy has an oestrogen like action, it must be ‘bad’ for oestrogen dependent cancers) and even rumours of misinformation from other industries who may be loosing some of their market share to soy foods.
Lets take a look at a few of the fears
Soy causes thyroid cancer: True and False: It has been known for a long time that a high soy diet may aggravate an existing underactive thyroid, though it has not been linked to cancer. This is termed a “goitregenic” food. Note that the cruciferous vegetables (of which brocolli and cabbage belong) are also goitregenic, yet are long associated with containing cancer preventing properties (indols).
Soy feminises little boys: Possibly. Does this cause any lasting negative effects? Undecided. Should you feed babies large amounts of soy? No. But this is largely because soy milk is not a breast milk substitute. Potentially all breast milk substitutes can be problematic. Furthermore approximately 1:4 dairy allergic children are also allergic to soy foods. I have witnessed an addiction like quality in some of these children, demanding over a litre of soy milk a day! I’d suggest that would be closer to an adult dose for a week. Soy milk is a relatively safe, calcium containing option to moisten cereal or use in cooking. The only ideal ‘milk’ in any large quantities for babies and toddlers is breast milk. For those who cannot be breast fed or are needing supplementation due to being picky eaters consider a low allergy formula. Cows milk is equally unsuitable and may be a source of exogenous hormones, allergies and a trigger of asthma, eczema, colic, hives and other common conditions.
Soy causes infertility in men: Unproven. This is based on a study when genistein (an isolated constituent of soy) was added to a live semen sample in a test tube. In 24 hours 1/3 of the sperm had died after being ‘sped up’ or hyperactive. The scientists concluded this may mean that sperm would not be able to swim properly and fertilize an ovum. At this point it seems to be a very wide hypothesis and not born out in any human studies.
Soy foods block the absorption of nutrients: True and False. Uncooked soy beans, edamame, contain a lot of phytates that are like ‘claws’ in plant foods that can affect nutrient absorption. Cooking fixes this problem. It is a similar issue in many grains and beans – foods which are rarely ever eaten uncooked.
The latest soy controversy is about soy supplements (ie: large, therapeutic doses of concentrated soy) and breast cancer. The study does not suggest soy containing foods are problematic (in fact some of us would suggest the opposite), yet the reporting of this story often featured soy foods. The concern is that pharmacological doses of soy may interfere with the bioavailability of the most commonly used drug used in the treatment of breast cancer. This is currently only an hypothesis, not proven in human studies.
The take home message.
There is no convincing evidence that eating moderate amounts of traditional soy foods in your diet will have negative health consequences, in fact they could offer many benefits (particularly around menopause in women). Phytooestrogens appear in many healthy vegetable based foods (beans, nuts, seeds etc) and it is interesting that soy has been singled out as being the bad guy in this argument. Almost all the negative studies involving soy fall into the category of not being on human, using isolates rather than the whole food sources, being hypothetical (if it has a weak oestrogen-like effect it will do all the negative things that oestrogen can sometimes do) or are statistically insignificant. The glaring exception is for people who have a goitre and the food guidelines include reduction of other healthy foods, not just soy.
Beyond genetic modification of soy (organic sources seem the safest option for now), the biggest health question mark hangs over soy isolates, soy extracts used in pharmacological doses and large amounts of hidden soy in a processed food diet.