Dear Sir
In
the highly informative review, “Soy products and the human diet,”
by Erdman and Fordyce (1), I was surprised at the authors’ conclusion
that “….soy formulas contain a less allergenic protein” than
cow-milk-based formula (CMF). Abundant literature on the
antigenicity and allergenicity of soy protein (SP) in infant
feeding fail to support the authors’ conclusion. The SPs
used in infant formulas appear to be equally and in some cases,
more antigenic than the heat-treated CMFs.
From an immunological and biochemical
standpoint, there is not a prior reason to believe that SP possesses
inherently hypoallergenic properties. May et al. (2) noted
the brisk antibody response in infants fed soy formula, whereas
Eastham et al. (3) concluded that SP is at least as antigenic
as cow-milk protein (CMP) and should be used with caution.
In animal models, investigators have been able to induce both
anaphylaxis and antibody production in guinea pigs, calves,
rabbits and mice.
Protein size
and diversity are important predictors of allergic response.
The large molecular weights and multiple protein subclasses
of SP rival the 20-30 antigenic fractions of bovine milk.
One author found up to 24 fractions of SP potentially capable
of antibody elicitation (4). Burks et al. (5), using enzyme-linked
immunoassays (ELISA) in infants with atopic dermatitis (soy
sensitised), demonstrated allergen-specific lgl: antibodies
to the 7S, IIS, and whey protein fractions of soy extract.
Other potentially allergenic or antinutritional substances found
with SP include lectins, soya saponins, trypsin inhibitors and
hemagglutinins. In addition, the molecular weights of
SP fractions range from 8,000 to 600,000 Da -certainly large
enough to stimulate antibody production and larger than most,
if not all, of the nutritional proteins found in cow milk (6).
Clinical
investigations with human infants validate the significance
of SP antigenicity. In the past 35 years, nine studies
compared the efficacy of SP – vs CMP-based formulas in the prevention
of atopic symptoms of food allergy (vomiting, colic, diarrhoea,
eczema, rhinitis and asthma) in infants at high risk of atophy.
Eight of these studies concluded that the incidence of atopic
disease was not effected by the exclusive feeding of soy formula.
In the most recent clinical study comparing CMF to soy-based
formula, Miskelly et al. (7) concluded, “…no evidence has so
far emerged to support that soya milk is better than cow’s milk
in regards to the risk of allergic disease.”
Finally,
the clinical literature is replete with numerous studies demonstrating
the deleterious effects of SP on multiple-organ systems.
SP ingestion or inhalation has been associated with asthma,
diarrhoea, anaphylactic shock, gastrointestinal injury and
the classical symptoms of atopy, i.e., eczema, rhinitis, vomiting,
diarrhoea, otitis media, etc. Cow-milk and SP allergy
may also occur simultaneously or as a consequence of soy feeding
after gastronintestinal insult. Hill et al. (8) found
that >50% of the infants with CMP intolerance were also reactive
to soy formula and Lothe et al. (9) demonstrated that 35% of
the CMP-allergic infants were also allergic to soy.
With its
inherent antigenic properties, lack of efficacy in preventing,
atopic disease and frequency of simultaneous allergy in CMP-sensitised
infants, one must conclude that SP is not hypoallergenic compared
with CMF (10). The American Academy of Paediatrics
Committee on Nutrition (AAP/CON) recommends against the use
of SP formulas in the dietary management of documented clinical
allergic reactions to CMP or in the routine management of colic
(11).
Although
soy-formula use is common in infants with suspected allergies
(~24% of the total formula market), its routine use as a hypoallergenic
substitute for CMP formulas is not supported by basic science
or clinical literature.
