To maintain safety standards, U.S. law and the Food and Drug Administration (FDA) govern the contents and safe production and distribution of all infant formulas.
When shopping for infant formula, you'll find several basic types.
Cow's milk–based baby formulas
Cow's milk–based formulas account for about 80% of the formula sold. Although cow's milk is the basis for such formulas, the milk has been changed dramatically to make it safe for infants. It is treated by heating and other methods to make the protein more digestible. More milk sugar (lactose) is added to make the concentration equal to that found in breast milk, and the butterfat is removed and replaced with vegetable oils and other fats that infants can more easily digest and are better for infant growth.
Iron-fortified baby formula
Cow's milk-based baby formulas have additional iron added. These iron-fortified formulas have dramatically reduced the rate of iron-deficiency anemia in infancy in recent decades.
Some infants do not have enough natural reserves of iron, a mineral necessary for normal human growth and development. For that reason, the American Academy of Pediatrics (AAP) currently recommends that iron-fortified formula be used for all infants who are not breastfed, or who are only partially breastfed, from birth to one year of age.
Additional iron is available in many foods (including baby food), especially in meats, egg yolks, and iron-fortified cereals. Low-iron formulas should not be used. Some mothers worry about iron causing constipation, but the amount of iron in infant formula does not contribute to constipation. Most formulas also have docosahexaenoic acid (DHA) and arachidonic acid (ARA) added to them, fatty acids, believed to be important for the development of a baby's brain and eyes.
Some formulas also are fortified with probiotics, which are types of "friendly" bacteria. Others are now fortified with prebiotics, in the form of manufactured oligosaccharides, in an attempt to mimic the natural human milk oligosaccharides, which are substances that promote healthy intestinal lining.
Extensively hydrolyzed baby formula
Another type of formula is extensively hydrolyzed formula, which often is called "predigested," since the protein content has already been broken down into smaller proteins that can be digested more easily. Ask your pediatrician to recommend a brand of hypoallergenic formula if one is needed for allergies or other conditions. However, these extensively hydrolyzed formulas tend to be costlier than regular formulas.
Soy formulas for babies
Soy formulas contain a protein (soy) and carbohydrate (either glucose or sucrose) different from milk-based formulas. They are sometimes recommended for babies unable to digest lactose, the main carbohydrate in cow's milk formula, although simple lactose-free cow milk–based formula is also available.
Many infants have brief periods when they cannot digest lactose, particularly following bouts of diarrhea, which can damage the digestive enzymes in the lining of the intestines. But this is usually only a temporary problem and does not require a change in your baby's diet. It is extremely rare for babies to have a significant problem digesting and absorbing lactose (although it tends to occur in older children and adults). While lactose-free formulas are fine sources of nutrition, check with your pediatrician before starting your baby on a lactose-free formula, since whatever problem they may be having is likely due to something else.
With a true milk allergy causing colic, failure to thrive, and even bloody diarrhea, the allergy is to the protein in the cow's milk formula. In this case soy formulas may seem like a good alternative. However, up to half the infants who have milk allergy are also sensitive to soy protein, and thus must be given specialized formula (such as amino-based or elemental) or breast milk.
Vegetarian & vegan concerns
Some strict vegetarian and vegan parents choose to use soy formula because it contains no animal products. Remember that breastfeeding is the best option for vegetarian families. And while some parents believe a soy formula might prevent or ease the symptoms of colic or fussiness, there is no evidence to support this.
The AAP believes that there are few circumstances in which soy formula should be chosen instead of cow's milk–based formula. However, one of these situations is in infants with a rare disorder called galactosemia; children with this condition have an intolerance to galactose, one of the two sugars in lactose. These babies cannot tolerate breast milk and must be fed a lactose-free formula. All states include a test for galactosemia in routine newborn screening after birth.
Specialized baby formulas
There are specialized formulas for infants with specific disorders or diseases, including for premature babies. If your pediatrician recommends a specialized formula for your infant, follow their guidance about feeding requirements (amounts, scheduling, special preparations), since these may be quite different from regular formulas.