THE SAFETY OF SOYA
Soya milk, made from soya beans, contains the same amount of protein as dairy milk. It also provides all eight of the essential amino acids which the human body requires. Soya milk is rich in polyunsaturated fatty acids including omega-3, and is free of cholesterol. Compared to cow’s milk, soya milk contains lower levels of saturated fat and higher levels of unsaturated essential fatty acids which can lower cholesterol levels in the body. Soya products provide an excellent source of B vitamins, calcium, iron and zinc. Soya also contains fibre which is important for good bowel health and can also lower cholesterol.
In recent years, soya milk and soya-based products have received much attention because of the phytoestrogens that they contain. Phytoestrogens are plant-made substances that can act in a similar way to the hormone oestrogen, although they are far less potent (Coldham et al., 1997). They are found in many fruits, vegetables, dried beans, peas, and whole grains. Isoflavones are a type of phytoestrogen found in soya beans and include genistein and daidzein. In general, much of the data indicates that isoflavones are beneficial to health. For example, isoflavones may have a protective role against heart disease. The UK’s Joint Health Claims Initiative (JHCI) offers pre-market advice and a code of practice for the food industry, enforcers and consumers, to ensure that health claims on foods are both scientifically truthful and legally acceptable. In 2002 the JHCI concluded its deliberations on a generic health claim for soya protein and blood cholesterol. The claim approved states that “the inclusion of at least 25 grams soya protein per day as part of a diet low in saturated fat can help reduce blood cholesterol” (JHCI, 2005). In addition to the benefits to heart health, isoflavones have been shown to offer other health benefits. For example, they may have a role in reducing menopausal symptoms; dietary soya supplementation has been shown to substantially reduce the frequency of hot flushes in some postmenopausal women (Albertazzi et al, 1998). While only a few clinical studies have examined the influence of phytoestrogens on bone health, a review of the current research states that the collective data suggests that diets rich in phytoestrogens have bone-sparing effects in the long term, in other words the data indicates that phytoestrogens may be beneficial to bone health (Setchell and Lydeking-Olsen, 2003).
Conversely, research focusing on the hormonal content of cow’s milk has not been widely discussed and surprisingly very little research has been published on this topic. Cow’s milk contains the hormones oestrogen, progesterone and a range of hormone precursors (androstenedione, dehydroepiandrosterone-sulphate, and 5ª-reduced steroids like 5ª-androstanedione, 5ª-pregnanedione, and dihydrotestosterone). Some researchers are particularly concerned about the oestrogen content of cow’s milk (Ganmaa and Sato, 2005), suggesting that cow’s milk is one of the important routes of human exposure to oestrogens. What concerns them is that the nature of cow’s milk has changed drastically over the last hundred years, in that for most of the time that a cow is milked, she is also pregnant and therefore secreting hormones into the milk. The levels of these hormones in cow’s milk increases markedly during pregnancy and has been linked to a wide range of illnesses and diseases including certain hormone-dependent cancers such as ovarian and breast cancer.
Consistent levels of soya isoflavones have been a component of the diet of many populations for centuries and the consumption of soya is generally regarded as beneficial for health with a potentially protective effect against a number of chronic diseases because of their oestrogenic activity. A recent review of the current literature concluded that when viewed in its entirety, the current literature supports the safety of isoflavones as typically consumed in diets based on soya or containing soya products (Munro et al., 2003).
Soya-based infant formula
Because soya-based infant formula is such a popular alternative to cow’s milk formula, it was decided to include a separate section on it here. Soya protein-based nutrition during infancy has a long history of safe use around the world dating back centuries. The first report of soya-based infant formula in the West was recorded in 1909 (Ruhrah, 1909) and soya-based infant formula was used in cases of infantile eczema as early as in the 1920s (Hill and Stuart, 1929). Since these early days soya-based infant formula has come a long way; it now contains all the nutrients needed by an infant and can be used as a safe alternative or supplement to breast milk if necessary.
Soya-based infant formulas have been more widely used in the UK since the 1960s and are currently fed to approximately one per cent of non-breast fed infants aged four to 10 weeks rising to approximately two per cent of infants aged 10-14 weeks (Hamlyn et al., 2002). However, the UK Foods Standards Agency advises that you should only give your baby soya-based infant formula if your GP or health visitor advises you to (FSA, 2005). They also state that in almost all cases, breast feeding or another type of formula will be a better choice, and suggest that if you are giving your baby soya-based infant formula at the moment, you should talk to your GP or health visitor about changing to a different formula (FSA, 2005). This reflects concerns about the use of soya-based infant formulas. Based largely on anecdotal and animal-based experimental evidence, these concerns have focused on the nutritional adequacy of soya-based infant formula, the effect of phytoestrogens, genetically modified soya and the effects of glucose syrup (which is used in place of lactose). These concerns are addressed below.
Soya-based infant formulas are formulated to meet all of the nutrient requirements of the growing infant. A number of studies have documented normal growth and development in infants fed soya-based infant formulas. One study compared weight, length and head circumference of healthy term infants to one year of age, fed either soya-based formula, or exclusively breast fed for at least two months then weaned on to cow’s milk formula. Results demonstrated similar growth in the first year of life between groups (Lasekan et al., 1999). Another, more recent study compared the nutritional status and growth of 168 infants who were allergic to cow’s milk and were fed either soya-based infant formula or extensively hydrolysed whey formula. Results showed that in both groups, nutrient intake and growth were within reference values confirming the safety and effectiveness of the soya-based formula (Seppo et al., 2005).
There is currently only one vegan infant soya formula on the market: Farley’s Soya Formula, produced by Heinz. This dairy-free infant formula is nutritionally complete and can be used from birth. It contains no animal products, so it is suitable for both vegetarians and vegans. It is also suitable for infants who require a diet free from lactose.
The role of phytoestrogens in the diet has become a somewhat controversial area with warnings focusing particularly on the safety of soya-based infant formulas. Various animal experiments (primarily using rodents and primates) have suggested that phytoestrogens can elicit oestrogenic effects with respect to sexual development and reproductive function. However, it is widely acknowledged that the results of animal experiments should not form the basis of a public health policy as significant differences in biological function between rodents, primates and humans make the interpretation of these types of experimental studies extremely difficult. Just one single human study has specifically examined the effect of soya formula feeding on sexual development and fertility (Strom et al., 2001). This study examined the association between exposure to soya formula in infancy and reproductive health in adulthood. The results provided no evidence of adverse clinical effects on sexual development or reproductive health of males and females. Indeed the authors of this study stated that their findings were reassuring about the safety of infant soya formula.
In 1998 a review on isoflavones, soya-based infant formulas and hormone function reported that growth was normal and no changes in timing of puberty or in infertility rates were reported in humans who consumed soya formulas as infants (Klein, 1998). The author concluded that soya-based infant formulas continue to be a safe, nutritionally complete feeding option for most infants.
However in 2003, in response to concerns about the oestrogenic properties of phytoestrogens the UK Department of Health’s committee of independent experts, the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) reviewed the health aspects of phytoestrogens as part of an ongoing programme of reviews on naturally-occurring chemicals (COT, 2003). This report attempted to assess, on the basis of current evidence, if ingestion of soya-based infant formulas poses any risk for human infants.
The report compared estimated dietary isoflavone intakes in Western and Eastern populations and found that Eastern populations have a significantly higher intake of phytoestrogens. While in the UK, the US, Australia and New Zealand isoflavone intakes tend to range from around 0.8 milligrams per day to 17.0 milligrams per day, intakes in Japan, China and Korea range from 18.0 milligrams per day to 200 milligrams per day. These figures do not include data collected from one group of vegans in New Zealand whose intake was found to be 140.0 milligrams per day (COT, 2003). The COT estimated that the daily isoflavone intake of a soya formula fed infant is approximately 40 milligrams per day (COT, 2003), above the average Western intake but well within the range of intakes seen in Eastern countries.
In a cautionary statement the COT warned that isoflavones may lower free thyroxine concentrations and advised that physicians and other health care workers be aware of possible interactions between isoflavones in soya-based infant formulas and thyroid function, particularly in infants with congenital hypothyroidism. That said, the report concluded that the findings from a wide range of studies did not provide direct evidence that phytoestrogens present in soya-based infant formulas can adversely affect the health of infants. However, they said that the findings did provide evidence of potential risks. For this reason, the Scientific Advisory Committee on Nutrition (SACN) considered there to be no substantive medical need for, nor health benefit arising from, the use of soya-based infant formulas and together with the COT recommended that the Department of Health reviewed current advice on the use of soya-based infant formulas.
The report did acknowledge that there is no evidence that populations which habitually ingest high quantities of soya (such as the Chinese or Japanese) have impaired fertility or altered sexual development. Despite this, they recommended that research should be undertaken as a matter of high priority to determine whether ingestion of soya-based formulas can affect infant reproductive development in any way. Interestingly, the United Kingdom and New Zealand are the only countries to have issued such advice with specific reference to phytoestrogens and soya-based infant formulas.
This is a controversial issue which has yet to be resolved. The FSA advise that, until a full review of the evidence both supporting and opposing soya formula has been completed, there is no reason to stop your baby having a soya formula if it has been suggested by a health professional. This it would seem is erring of the side of extreme caution given that thousands of babies have been raised on soya-based infant formula.
Genetically modified soya
It is relatively recently that the genetic modification (GM) of organisms (plants and animals) has developed as a technology. However, GM technology has not been welcomed by the British public; many people are deeply suspicious and mistrustful of the science. We have been reassured in the past that certain foods are quite safe to eat only to find that they are not. Many of us will remember in 1990, just before the bovine spongiform encephalopathy (BSE) crisis, John Gummer feeding his daughter a beef burger and saying that beef was perfectly safe, it was not.
The mistrust remains and many questions have gone unanswered. For example, have the transgenic plants grown so far met expectations? Evidence suggests that in many cases they have not met the high yields expected. What is the real risk of transgenic contamination between genetically modified (GM) and unmodified plants? This question refers to the contamination of an unmodified crop with pollen from a GM plant. The pollen of the GM plant will carry copies of the foreign genes that were used confer some additional characteristic to the plant. These may encode pesticide resistance for example along with antibiotic resistance marker genes that were used to identify the successfully modified plants when they were first produced. The question of contamination is difficult to answer as it may be years or even decades before we can assess the full extent of transgenic contamination, but so far evidence suggests widespread contamination has occurred in some parts of the world.
Another concern is that the genetic material (DNA or genes) may be transferred from GM foods to bacteria in the human gut and from there into human tissue. There is experimental evidence that DNA from GM soya has been taken up by bacteria in the small intestines of human volunteers (Netherwood et al., 2004). This raises concerns that bacteria in the gut (for example Lactobacillus) might then transfer that DNA into our intestinal epithelial cells. What effect this may have on human health will largely depend on what the gene does; it may do nothing but is that a risk worth taking? Finally, as a result of a lack of funding, scientists are sometimes forced to adopt the corporate agenda, which is not necessarily the same as the public good. For example, Monsanto has used genetic engineering to produce herbicide resistance crops thus increasing sales of its herbicide Roundup.
GM products, especially soya and maize, are now in so many foods, including baby milks, that it can be difficult to avoid them. We do not yet know enough about this technology to confidently say what the long term effects of it will be but consumers appear to be voting with their shopping baskets by avoiding GM foods as far as possible. The good news for vegan babies is that Heinz state that no GM ingredients at all are used in Farley’s Soya Formula (Heinz, 2005). In addition, SMA Nutrition and Cow and Gate also state that no GM soya is used in their soya-based infant formulas (SMA Nutrition, 2006; Cow and Gate, 2006).
Glucose syrup and tooth decay
Another concern with infant soya formula is that the glucose syrup content may harm teeth. All infant formulas must comply with standards laid down by UK regulations which specify minimum and maximum amounts of carbohydrate (the body’s main form of energy). The carbohydrate in cow’s milk is the sugar lactose, in soya-based infant formula an alternative carbohydrate is used: glucose syrup. Glucose syrup is often confused with sugars but in fact is derived from corn starch and is not the same as glucose or syrup. It is mainly made up of beneficial complex carbohydrates (starches) rather than simple carbohydrates (sugars) which are known to be harmful to teeth. Research has shown that soya infant formulas are no more likely to cause tooth decay than other infant formulas (Moynihan, 1996).
Tooth decay can be the result of many factors, not only the presence of sugars in a food and drink but howthey are consumed. It has been shown that prolonged contact of sugary foods and drinks with teeth increases the risk of tooth decay significantly. Children should be encouraged to drink water if they are thirsty as it quenches the thirst, maintains body fluid levels, does not spoil the appetite and is safe for teeth. Fresh fruit juice provides a good source of vitamin C and can be given with meals to help the absorption of iron. However, fresh fruit juices are acidic so may be harmful to teeth and should be diluted with water. Furthermore, juice should be served in a cup rather than a bottle to minimise the risk of tooth decay. Children should be discouraged from consuming sugary carbonated drinks and squashes as these contribute to dental problems, are a poor source of nutrients and tend to displace other more nutritious foods. If normal weaning practices are adopted, soya infant formulas should not cause harm to teeth (Moynihan, 1996).
In summary, soya-based infant formulas continue to provide a safe feeding option for most infants. They meet all the nutritional requirements of the infant with none of the detrimental effects associated with the consumption of cow’s milk formulas.