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Policy
Statement of Royal College of Australian Physicians
The lack of a suitable diagnostic test
for food intolerance has allowed for an exaggeration of the
incidence and a tendency for over-diagnosis. The true incidence
of milk intolerance in our community is difficult to ascertain
but a reasonable working figure would be 2.0% (1).
The number of infants on soy formula outweighs
this figure as soy formula accounts for approximately 10%
of formula sales in Australia.
There is no
evidence
that soy formulas are nutritionally better than cow's milk
formula for normal infants. The assumption that
symptomatic infants who improve on soy formula are therefore
intolerant of milk protein is addressed in this statement
(2).
There are several well-characterized disorders
caused by cow's milk protein intolerance (CMPI), including
cow's milk allergy, cow's milk enteropathy and cow's milk
colitis. There is also a range of vague signs and symptoms
ascribed to CMPI, which includes excessive crying, vomiting,
wind, colic, vague ill health, and tension-fatigue syndrome
(3).
With the latter symptoms, there is usually
no evidence of associated chronic diarrhea or growth failure.
Of concern, is that many of these latter symptoms may be the
result of parent-child relationship problems, which are inappropriate
to treat with soy formula. Controlled trials of cow's milk
and soy formulae in colicky infants have not demonstrated
a benefit from soy formula (4).
The rationale for the use of soy formula
is the assumption that soy protein is less antigenic than
cow's milk protein and thus should be used in the treatment
of CMPI, or prophylactically in patients at high risk for
developing CMPI.
Soy protein
can cause intolerance reactions
with gastrointestinal symptoms as well as acute anaphylaxis
and up to 40% of infants intolerant of cow's milk also develop
soy protein intolerance (6).
Studies show that feeding soy formulae
from birth in infants at increased risk of developing allergy,
does not have a beneficial effect (7-9). Eastham et al, in
a prospective feeding trial, showed soy protein to be at least
as antigenic as cow's milk protein (8).
Miskelly et al, in a randomized clinical
trial of cow's milk vs soy protein formulae in children with
family histories of atopic disease, demonstrated a similar
incidence of wheezing and eczema between the groups and an
increased incidence of napkin
rash, diarrhea and oral thrush in the group fed soy formula
(9).
Thus, it seems that soy formula is inappropriate
even in cases of proven CMPI, because of its ability to cause
reactions. In cases of true gastrointestinal CMPI, the use
of protein which has been hydrolyzed to the point that it
is no longer antigenic, is preferred.
Soy protein contains only one-third of
available nitrogen as essential or semi-essential amino acids
(10) and therefore has a
lower biological value than milk protein.
Soy may cause loss from the gut of vitamins,
minerals and trace elements and it has been suggested that
10% more calories are needed
in soy preparations in order to promote equivalent
growth to infants breastfed or fed a milk formula (11). Low
levels of chloride have been reported and may result in serious
hypochloraemic alkalosis in infants fed soy formula (12).
Manufacturers currently attempt to compensate
for these potential problems by adding extra protein, trace
elements and chloride to soy formulae. Growth of infants fed
soy formulae is similar to that of infants fed formulae based
on cow's milk protein but there is concern about poorer bone
mineralization in infants fed soy formulae (13).
The carbohydrate content of soy formula
differs in each of the three commonly available preparations
(Isomil: sucrose 36%, corn syrup solids 64%; Prosobee: maltodextrins
100%; Infasoy: sucrose 25%, corn syrup solids 75%). Sucrose
is not the preferred carbohydrate in infancy because of its
potential effect on teeth and development of inappropriate
eating habits.
High aluminum content has also been documented
in soy formula (14).
Soy is also a rich source of phytoestrogens
(nonsteroidal estrogens of the isoflavone class). It
is unclear whether these are beneficial (protect
against breast and prostate cancer) or harmful (result in
infertility and liver disease) (15).
It is also possible that soy formula impairs
immunity. Infants fed soy formula had lower
levels of antibodies in response to routine immunizations
and more infections
than those fed human milk or cow's milk formula (16).
Policy
Statement of Royal College of Australian Physicians
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