Phyto-oestrogens in baby food based on soya bean protein
Paediatrica, 8 (5), 1997
Preliminary Remarks
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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