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The Soya StorySoya: the health protector - The health effects of Soya
Phytoestrogens Isoflavones are a type of phytoestrogen and include genistein and daidzein. Each gram of soya protein in traditional soya foods provides about three to four milligrams (mg) of isoflavones (Messina and Redmond, 2006). They may act in a similar way to the animal hormone oestrogen (Coldham et al., 1997), but they are much weaker, between 100 and 100,000 times weaker (Messina et al., 2006). Because of this, some scientists suggest that phytoestrogens may actually have a normalising effect on the body’s natural oestrogen levels (Kurzer, 2002). They may do this by partially blocking the strong oestrogen signal that occurs in people with high levels of oestrogen, for example women taking the contraceptive pill or HRT. On the other hand, phytoestrogens may boost the weak oestrogen signal in people with low levels of hormone, such as in postmenopausal women. 
Ironically, much of the controversy surrounding the supposed harmful effects of soya foods focuses on phytoestrogens. There have been numerous scare stories ranging from outlandish claims that they can feminise boys and make men grow so-called ‘man boobs’ to more serious reports that they can alter sexual development and fertility. These reports are based on in vitro (test tube) and animal experiments which bear no relevance to humans. These experiments are fundamentally flawed on many levels. Firstly, isoflavones behave differently in different species so animal studies are not applicable to humans. Secondly, the intestines act as a barrier to isoflavones so artificially boosting levels in animals by injection has no relevance. Finally, many of these experiments have exposed animals to isoflavones at levels many, many times higher than those absorbed by infants fed with soya-based infant formula. More and more scientists and doctors are acknowledging that the results of animal experiments should not form the basis of a public health policy. Dr Kenneth Setchell, Professor of Paediatrics at Cincinnati Children’s Hospital Medical Centre, states that mice, rats and monkeys all metabolise soya isoflavones differently from humans and that the only appropriate model for examining human reproductive development is the human infant (Setchel, 2006). There are no human studies that support these stories but they still have caused undueconcern among many people. Although phytoestrogens in soya have been a part of the diet of millions of adults and children in Asia for centuries, they continue to be regarded with some suspicion. In 2003, amid concerns about the effects of phytoestrogens on infants consuming soya formula, the UK Department of Health’s Committee on Toxicity (COT) published an extensive review on the health implications of phytoestrogens (COT, 2003). Their aim was to assess if soya infant formulas posed any risk for infants. 
They compared isoflavone intakes around the world and found that they varied widely from just 0.8-17.0mg per day in the UK, US, Australia and New Zealand to 18-200mg per day in Japan, China and Korea. Some groups in the UK were found to be consuming relatively more isoflavones, for example infants fed soya formula, different ethnic populations, vegetarians and vegans. Eleven breastfeeding vegan mothers had an average intake of 75mg isoflavones a day; higher than the average UK intake but well within levels seen in some Asian countries. Infants fed soya formula were estimated to be consuming around 23.6mg isoflavones per day (4mg for every kg of bodyweight). Again, higher than average intakes in the UK but within levels seen in Asia. More recently, the isoflavone intake of a group of UK vegetarians and omnivores was estimated using a new database which lists the isoflavone content of 6,000 foods (Ritchie et al., 2006). Vegetarians were found to consume just 7.4mg per day compared to an estimated 1.2mg for omnivores. The main source for each group were soya milks and yogurts, soya and textured vegetable protein foods, breads and dried fruit. So while isoflavone intakes vary widely both between and within populations, vegetarians, vegans and infants consuming soya formula are not exposed to levels higher than those seen in many Asian countries. The COT report acknowledged that there is no evidence that people who regularly eat high quantities of soya, such as the Chinese and Japanese, have altered sexual development or impaired fertility. It should be remembered that China is the world’s most populous nation, with over 1.3 billion citizens, that have been consuming soya for over 3,000 years!
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The Soya Story - ContentsResources:
Myth-Busting Soya and the Environment FAQs Soya research |
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By Dr Justine Butler
The Soya Story
The Safety of Soya 
Soya-Based Infant Formula 
The Soya Saga  |
Vegetarian & Vegan Foundation Top Suite, 8 York Court, Wilder Street, Bristol, BS2 8QH, UK T: 0117 970 5190 W: www.vegetarian.org.uk E: info@vegetarian.org.uk |
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