Within a very short time frame – a decade or two – soya has infiltrated our daily diets to a spectacular degree. Believe the PR spin and this simple plant-based food – which can be eaten in so many different ways – not only fights disease but also improves longevity.
In the food business there is a simple maxim that keeps us buying and eating: if a little is good for you, a lot must be really good for you. It’s nonsense, of course, and in the case of soya it may even be dangerous.
Certainly, soya has some proven benefits. It contains, for instance, isoflavones, plant estrogens that in small amounts may have cancer-preventing properties. It is low in fat and is a reasonable source of protein. In the US, food labels are allowed to claim that soya is ‘heart-healthy’.
Soya also has the benefit of Eastern mystique. Health claims for soya, for instance, are often based on the fact that Oriental peoples have eaten it for a millennium and have lower rates of cancers of the breast, ovary and testicles than we do in the West. All true, but equally such claims ignore the fact that the Japanese, and Asians in general, have much higher rates of other types of cancer, particularly cancer of the oesophagus, stomach, liver and pancreas.
Likewise, we in the West eat soya in quantities and ways that are simply not healthy.
Soybeans, as found in nature, are not suitable for human consumption. Only after fermentation for some time, or extensive processing, including chemical extractions and high temperatures, are the beans – or the soya protein isolate – suitable for digestion. A diet high in soya is a diet high in plant estrogens. Research studies in both humans and animals have found that isoflavones in soya can have a profound effect, raising levels of oestrogen significantly. Proponents claim plant estrogens are ‘safer’ because they are natural, but this is simply not true. High levels of circulating oestrogen are a cancer risk – whatever the source.
It might be worth the risk if soya had an unquestionable record of health benefits, but here too the data is lacking.
In August 2005, a report for the Agency for Healthcare Research and Quality, at the US Department of Health and Human Services, reviewed data from 200 studies into the relationship between soya consumption and a number of health outcomes. A wide variety of soya products was studied, including foods such as soybeans, soya flour, soya milk, tofu, miso, tempeh, natto and okara, isolated and textured soya protein that is added to foods, and soya-derived isoflavone supplements.
When it came to improving blood pressure and levels of high-density lipoprotein (HDL, known as ‘good’ cholesterol), soya consumption did not produce any significant effects.
For menopause-related symptoms there was a net reduction in hot-flush frequency ranging from 7 per cent to 40 per cent. However, the review noted that the trials were mostly poor quality, which made definitive conclusions difficult. No other menopausal symptoms were studied.
The review also found insufficient data to suggest that soya had an effect on bone health, cancer, kidney disease, endocrine function, reproductive health, neurocognitive function or glucose metabolism. Aside from minor gastrointestinal problems reported in some short-term studies, consumption of soya products by study participants was not associated with adverse events, though the reviewers noted long-term safety data were lacking.
Soya proponents often argue studies that do show adverse effect use high doses of soya that are not relevant to real-world conditions, but how would they know? Some form of soya, usually the protein isolate, is in 60 per cent of all processed food, which means most of us eat soya, without thinking and without knowing, every single day.
Soya flour is used in bread; soya oil is in margarine and is the main component of the ubiquitous ‘vegetable oil’ found in a variety of food products. If you eat conventionally reared meat you are eating soya-fed animals. Soybean concentrate is used to bind foods together and boost protein content, and soya lecithin, the emulsifier E322, is one of the most widely used food additives. It is found in health drinks, ice creams, yoghurts, meat substitutes, sweets, infant formula, bakery goods, breakfast cereals, drinks, margarine, pasta and processed meats.
Soya-based infant formula milk is widely available, often on the same shelves as varieties based on cow’s milk, and is currently given to around 3 per cent of infants in the UK. This soya milk still contains isoflavone, exposure to which may impact on future fertility and reproductive development. The Government advises parents not to use soya-based formula without medical supervision, yet there is nothing to prevent parents using soya formula; neither are there any warnings on the packs.
In 1998, in the American Journal of Clinical Nutrition, investigators reported that circulating concentrations of isoflavones in infants fed soya-based baby formula were 13,000 to 22,000 times higher than plasma oestradiol (naturally produced oestrogen) concentrations in infants fed baby formula made with cow’s milk.
Most recently, a study at the Harvard School of Public Health, in Boston, found that men who regularly ate soya had significantly lower sperm counts.
Our enthusiasm for all things soya also means we ignore the fact that all soya is not created equal. Traditional fermentation of soybeans significantly reduces some of its harmful properties (see box, below). As a result, soya products such as tempeh and miso can be beneficial if eaten in moderation, but non-fermented soya products such as tofu and soya milk may be less beneficial.
Finally, soya is an environmental concern. Huge tracts of rainforest are being cut down to feed our greed for this ‘healthy’ food, and to improve yields farmers are encouraged to grow genetically modified varieties, which require even more pesticides.
It seems heresy in a world drowning in soya, but it is possible to have a healthy diet and never eat soya at all. Given the way we have allowed it to infiltrate the food system, though, it would now take a monumental effort to exclude it entirely from your diet – a situation that makes a mockery of the notion of informed consumer choice.
A very large percentage of soya – more than 90 per cent – is genetically modified, and soya also has one of the highest percentages of contamination by pesticides of any of the foods we eat.
The usual recommendation is to eat organic soya to avoid GM contamination. Apart from the fact that organic soya doesn’t do much to help avoid rainforest destruction, the bad news is that GM soya has been found in a range of food items labelled ‘organic’ or ‘GM-free’.
A 2004 study at the University of Glamorgan, published in the British Food Journal, found that one-fifth of soya-based products on sale at health food shops and supermarkets contained as much as 0.7 per cent GM material. The products included vegetarian burgers, cheese substitutes, soya milk, vegetarian sausage mix, soya beans and soya flour. Although companies have to declare GM contents only over 0.9 per cent, it is well known that the Soil Association standard for organic products is 0.1 per cent.
What’s wrong with soya?
- Allergens Soya allergies are on the rise as soya consumption goes up. These days, allergies to soya proteins – the symptoms of which include rashes, diarrhoea, vomiting, stomach cramps and breathing difficulties – are almost as common as those to milk.
- Phytates These substances can block the uptake of essential minerals – such as calcium, magnesium, iron and especially zinc – in the intestinal tract. All beans contain phytic acid, but soybeans have higher levels than any other. Oriental children who do not consume fish or meat products to counterbalance the effect of their high-phytate, soya- and rice-based diets have been shown to suffer nutritional deficiency illnesses, stunting, rickets and other developmental problems.
- Enzyme inhibitors Soya contains potent enzyme inhibitors, which block the action of trypsin and other enzymes needed for protein digestion. Normal cooking does not deactivate these substances, which can also cause serious gastric distress and reduced protein digestion, and can lead to chronic deficiencies in the uptake of essential amino acids such as methionine and leucine, as well as isoleucine and valine. These are all needed to combat stress, avoid depression, synthesise new body protein and maintain a healthy immune system.
- Hemagglutinin Soya products also contain another chemical, hemagglutinin, which promotes clumping of red blood cells. These clumped red cells are unable fully to take up oxygen and carry it, via the bloodstream, to the body’s tissues and organs. Hemagglutinin has also been observed to act as a growth depressant. Although the process of fermenting soybeans does deactivate hemagglutinin, cooking and precipitation do not.
- Phytoestrogens Soya contains high levels of oestrogen mimics known as isoflavones, which can disrupt hormone function in both men and women. High levels of circulating oestrogens are a risk for certain types of oestrogen-dependent cancers, for instance of the breast, ovaries and testicles. Animal studies have linked high consumption of isoflavones with infertility and reduce immunity.
- Antithyroid agents The plant oestrogens in soya can also cause an underactive thyroid and are implicated in thyroid cancer. In infants, consumption of soya formula has been linked to autoimmune thyroid disease.
- Aluminium To manufacture soya protein isolate – the high-protein derivative of soya that is used in snacks, infant formulas, protein bars, breakfast cereals, baked goods, ice creams and yoghurts – soybeans are first mixed with an alkaline solution to remove fibre, then precipitated and separated using an acid wash and, finally, neutralised in an alkaline solution. Acid washing in aluminium tanks leaches high levels of aluminium into the final product. As a result, soya-based formula can contain around 1,000 per cent more aluminium than is found in conventional milk-based formulas.
This article first appeared in the Ecologist December 2008