Protein requirements, infant: Proteins contain different amino acids that are linked together. Proteins provide both calories and the amino acid building blocks that are necessary for proper growth. The protein in human milk provides between 10%-15% of an infant's daily caloric need.
Casein and whey are the two major proteins of human milk and most milk-based formulas. (Immunoglobulins, a type of protein unique to breast milk, provide infection-fighting immunity, are not efficiently metabolized, and are therefore not considered as a nutritional source.) While manufacturers may vary slightly in the relative proportion of these two proteins, healthy babies generally thrive on any milk-based formula brand.
Some 0.5%-7.5% of infants have a true allergy to the cow proteins that are in milk-based formulas. Infants with true cow milk allergy can develop abdominal pain, diarrhea, rectal bleeding, skin rash, and wheezing when given milk-based formulas. These symptoms will disappear as soon milk-based formula is removed from the diet. (Allergy to cow milk protein is different from lactose intolerance). Treatment of cow milk protein allergy involves using formulas that contain no cow milk, or using formulas that contain "predigested" casein and whey proteins. The predigesting process breaks the whole proteins into smaller pieces or into amino acids. The amino acids and smaller protein pieces are non-allergenic (do not cause allergy).
Soy protein formulas contain no cow milk, and are reasonable alternatives for infants with true cow milk allergy. Since most soy-protein formulas also contain no lactose, they are also suitable for infants with lactose intolerance. The carbohydrates in soy-protein formulas are sucrose, corn syrup solids, and cornstarch or glucose polymers.
Certain infants have allergy to both cow milk proteins and soy proteins. These infants require a formula in which the cow milk protein (casein) has been "predigested" and specific amino acids added to provide a formula that can provide proper nutrition. The decision to utilize one of these specialized formulas should be made in consultation with the infant's pediatrician.