Cow milk protein contains
two major fractions: casein and whey. Remember the childhood fable, “Little
Miss Muffett, sat on a tuffet, eating her curds and whey”? Well, she was
eating cottage cheese. The “curds” are actually casein, and the more digestible
“whey” is the liquid protein that floats on top. Soy
protein is significantly different in composition from cow milk
protein, but both are modified to more closely resemble the amino acid
content of human milk (human milk protein is actually 40% casein and 60%
whey). The carbohydrate in whole cow milk-based formulas is lactose. This
disaccharide (comprising two basic carbohydrate units) is the naturally
occurring sugar in all mammalian milks, including human milk. Lactose,
in addition to providing an important energy source, also enhances the
absorption of calcium. Soy formulas generally contain either sucrose (table
sugar) or corn syrup. Fats in all formulas are “engineered” from a variety
of sources.
Cow milk or soy?
So, the question remains—should you decide not to breast
feed, which formula should you give your baby? In most cases, I recommend
cow milk protein-based formula, either Similac (Ross Laboratories) or Enfamil
(Mead Johnson).
Soy formula really has little use as the primary source
of infant feeding. First, in those infants who are allergic to cow milk,
soy protein cross-reacts immunologically with cow milk protein in 5-30%
of cow milk protein-allergic infants, causing the same allergic reaction
that results from cow milk protein. Therefore, it really has no place in
the initial management, or prevention, of milk allergy. Second, lactose,
which is absent in soy formula, is the best carbohydrate source for normal
infants.
