Phyto-oestrogens in baby food based on soya bean protein

At its last meeting for the year 1996 the (Swiss) Federal Commission on Food (German initials EEK) discussed the question of oestrogens in food. The fact that substances with an Oestrogenic effect occur naturally and in large quantities in the soya bean and are also in mother's milk substitutes based on soya bean protein has led to worldwide concern. The EEK decided not to issue a general warning, but to send out an Information Sheet direct to paediatricians. The then President of the Commission, Omar Tönz, is hereby fulfilling his obligation to do so.

The summary below is based on a current study of the problem by B. Zimmerli and J. Schlatter BAG, Department of Food Science: "Existence and Development of Isoflavones Daidzein and Genistein in Baby Food". Communication regarding Foodstuffs in Hyg. 88, 2 19-232 (1997), which includes bibliographical references and other technical details.

Phyto and Xeno-oestrogens in food and the environment

Food consumed by humans contains a large number of natural substances the exact biological effect of which is still insufficiently clear. We have known, however, for some time that plants contain substances with an oestrogenic effect (phyto-oestrogens) and in concentrations which show a recognisable oestrogenic effect in model and animal experiments. In Australia it was established that infertility occurred in sheep fed on clover which contained oestrogens, and had developed clover disease. These substances occur in numerous plant foodstuffs, especially in the leguminous plants and also in the soya bean.

In addition, we are frequently warned against a number of environmental chemicals which likewise produce an oestrogenic effect - the xeno-oestrogens. They are blamed for possibly being responsible for the continual lowering of the sperm count in men and for the fact that various fertility problems are also observable in wild animals. The fact that the concentrations of the xeno-oestrogens in foodstuffs is up to 10,000 times lower than that of the phyto-oestrogens must not lead us into minimising the importance of this retrograde situation but rather urge us to regard the problem of the phyto-oestrogens as at least equally serious.

Soya bean problems

The soya bean is indisputably regarded worldwide as one of the most important and profitable food plants which, because of its high albumen and total energy content, has an excellent cost effective ratio. Unfortunately this "cow of China" has certain disadvantages.

The raw product contains several substances which are not completely without problems for food consumed by humans, particularly baby food. First of all, there is no doubt that the soya bean is a very powerful allergen. Next, it contains too little methionine, which therefore has to be added during the production of baby food. (For some time now in China, egg yolk rich in methionine, has been added to soya milk). Undesirable substances such as trypsin inhibitors or haemagglutinine (lectin) are eliminated by heat treatment. Phytase is used to eliminate phytic acid. In the 50-60s when it was necessary to determine whether goitre was caused by soya bean flour, the presence of goitrous substances was postulated, but could never be precisely identified. For all that, manufacturers feel bound to add iodine to these products to guard against this occurrence. It may be mentioned, as a marginal note, that finally calcium, magnesium and other trace elements have had to be added as well.

Finally there remains to include as undesirable substances the isoflavones Genistein and Daidzein, both of which exhibit oestrogenic properties. Their chemical structure reminds one faintly of oestrogens or the steroidal hormones. Since the relevant receptors are extremely old in the development of evolution, they are not particularly specific, but can bind these substances and make them endocrinologically active. They are naturally 100-150,000 times less active than the corporal b-oestradiol. The soya bean products registered in Switzerland for infants - SOM (Milupa), Humana SL (Milchwerke Westfalen, Herford) and Mamina Soya (Wander) contain 280-980 mg per gram of dry weight of the above mentioned isoflavones. A baby which is fed solely on such products receives a daily amount of 6-20 mg/kg of such substance. This corresponds to 8-25 times the amount which extends the cycle in women.

Metabolism and biological effect of isoflavone

After separating from the glycerides with which they are bound, genistein and daidzein are absorbed and further metabolised in the liver (glucuronisation) and finally excreted in the urine. Like bilirubin or similar sex hormones, they have an enterohepatic cycle. Their plasmic half-life is 7 to 8 hours in adults and considerably longer in infants.

Isoflavones also occur in milk, so that the breast fed baby also receives small amounts if the mother consumes soya bean products. Similarly these substances may also be found in cow's milk in quantities which vary with the type of fodder used. According to an American study of a group of 4-month old male infants who were either breast fed, or fed with a cow's milk or a soya bean based preparation (isomil), approximately 3.25 or 180 mg of isoflavone were found to have been excreted in the urine each day. More recent measurements on infants fed entirely on soya bean preparations showed plasma concentrations of 0.5-2 mg/ml. Compared with the concentrations of 30-60 pg/ml of oestradiol, this corresponds roughly to 20,000 times the amount of isoflavone. By comparison, the endogenous oestradiol in women is between 30 and 200 mg/ml.

Other effects of isoflavone include inhibiting peroxidation of lipids (anti-oxidative effect), and inhibiting angiogenesis. According to their concentration in vitro genistein and daidzein can slow up or stimulate the growth of tumorous cells. Other effects are stimulation of the synthesis of protein which binds the sex hormones, and inhibition of the enzyme aromatase.

Evaluation

In animal experiments the administration of isoflavone to foetuses and new-born animals resulted in negative effects as regards feminisation (of course the doses given were distinctly higher than those for a baby fed on soya bean products).

On the other hand soya bean has been used as a baby food in China for about 70 years and in the USA for at least 40 years to a relatively large extent. No negative effects have so far been established. However, targeted studies were never made, such as are now to be undertaken in the USA. In the Asiatic countries it was speculated that perhaps genetic adaptation may have taken place during the 5,000 years of normal consumption of the soya bean. In those parts of the world consumption of the soya bean is associated with a decrease in the prevalence of cancer and cardio-vascular diseases.

It is clear that chronic effects of high doses of isoflavone on the human being have been poorly or never researched. Experiments with the synthetic hormone di-ethylstilboestrol, which had been used for dozens of years to prevent abortion, and led to an increase in cervical and vaginal carcinoma only in the offspring of the women concerned should give cause for thought in this connection.

Conclusion

As a baby food, and particularly as a substitute for mother's milk, very restrictive use should be made of soya bean products, especially if potentially harmful effects for babies and small children have not been investigated scientifically or if isoflavone has not been successfully eliminated during preparation of the product. (That the, in any case, already expensive production has to be further complicated by yet another biotechnological concept should be mentioned only in brackets). In New Zealand, some people called for an absolute ban, while in the USA they officially ask for restrictions. In our country, soya bean products should not be used routinely in food prepared for healthy babies, and are subject only to a few medical indications (intolerance of lactose, galactocaemia, possibly intolerance of cow's milk or allergy); and in no case for ecological, ideological or ethical reasons. But in any case hydrolysed or lactose-free products based on cows s milk are probably better than those based on the soya bean.

O. Tönz, Lucerne

B. Zimmerli, Bern

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