Steven Schwarz, MD
For expectant parents, a decision regarding the method of feeding their new baby is often a difficult one. Should I breast feed my baby? Is formula really bad for my baby? I wasn't nursed, so why should I nurse my baby? These are but a few of the questions pediatricians are asked in their daily practice.
Until the mid-twentieth century, choices were limited: most infants were fed either breast milk or a "formula" prepared from evaporated cow milk. Today, parents (and pediatricians) are inundated with advertisements from formula companies, touting their products as "closest to mother's milk", "most digestible", "hypoallergenic", etc. One thing is certain; for virtually all newborns, breast milk represents the ideal dietary source. It contains both nutritional and non-nutritional factors that have not been duplicated in commercial preparations.
Nevertheless, some mothers may not be able to breast feed because of specific maternal or infant medical conditions. For others, the choice to use a human milk substitute is based upon personal, family and career considerations. As a pediatrician, I encourage expectant mothers to exclusively nurse their infants if at all possible (a position fully supported by the American Academy of Pediatrics). However, when a formula feeding approach is chosen, parents should be made aware of the available products and their uses.
Formula Versus Breast Milk
In an attempt to mimic the composition of human milk, commercial infant formula manufacturers have come very close to providing a similar content of amino acids (the building blocks of protein) fats and carbohydrate in their products. However, despite technological advances in formula preparation, these human milk substitutes lack many compounds found in human milk, including:
- Anti-infective agents: Human milk contains cells, antibodies and other factors that inhibit the growth of potentially harmful bacteria in the intestine and provide protection against specific bacteria, viruses and potentially allergenic foreign (non-human) proteins.
- Enzymes: Specific compounds, found in human milk, aid in digestion of nutrients, especially fats.
- Trophic factors: These proteins in human milk are known to stimulate cell growth and division.
Breast-fed infants have been shown to have a lower incidence of certain infections than formula-fed infants, and they may also have fewer allergies later in life. Clearly, breast is best. However, if you decide to use formula for your baby, commercially available products will support normal growth and development.
Choosing The Right Formula For Your Baby
Casein, whey, soy, hydrolyzed, lactose, sucrose, disaccharide-free, lactose-free, hypoallergenic -- these are but a few of the unfamiliar words on formula labels. The vast majority of babies fed a human milk substitute are given modified cow milk or soy protein-based formula.
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.
But doctor, I was told my baby is allergic to lactose. This is a statement I frequently hear. In reality, you can't be allergic to lactose. Remember, the sugar in human milk is lactose. Parents are really referring to lactose intolerance caused by the absence of an intestinal digestive enzyme that results in gas and diarrhea following lactose ingestion. Lactose intolerance can occur in some babies following a prolonged bout of gastroenteritis (usually, diarrhea caused by a virus). Thus, your doctor may recommend lactose-free soy formula, or cow milk protein based Lacto-Free (Ross), after an episode of gastroenteritis that persists beyond 3 to 4 days. However, lactose intolerance is extremely rare in all other infants.
Low iron formulas
Iron deficiency anemia probably represents the most commonly encountered nutritional problem during infancy and childhood. Babies who are not breast-fed are at significant risk of developing iron deficiency. This occurs for two reasons: first, commercial formulas are extremely low in iron content (unless the formula is supplemented with iron), and second, because the intestinal absorption of dietary iron is much greater in breast vs. bottle-fed infants. Thus, I recommend that all formula-fed babies receive an iron-supplemented preparation.
Can my baby develop iron toxicity from these supplemented formulas? In a word ..no! These formulas are completely safe, and they will prevent anemia that may need to be treated in the future.
Doesn't iron cause constipation? Certainly, iron overload may be associated with constipation. However, the vast majority of infants tolerate supplemented formulas without difficulty.
How Much? How Often?
Determining how much to give a breast-fed infant is easy -- babies will nurse until they are satisfied, and the volume of intake is impossible to measure. Formula-fed infants, however, are often encouraged to drain the bottle. Not uncommonly, I see a one month-old baby consuming 6 or more ounces every 4 hours!
As a general rule, you should add 3 ounces to your baby's age in months, to determine the amount of formula consumed on an every 4-hour schedule (until she sleeps through the night). Thus, at one month your baby will take 4 ounces, at two months 5 ounces, and so on. When your baby wants to consume more than 32 ounces of formula per day (usually by 4 to 5 months), she should be ready to supplement her diet with solid foods. Whole cow/s milk should not be introduced until at least 10 months of age.
Understanding Formula Intolerance
With the exception of temporary, post-gastroenteritis associated lactose intolerance, most problems related to formula intolerance are caused by an allergy to specific proteins. Colic, excessive spitting-up, feeding-related irritability, rectal bleeding, diarrhea, constipation and gas are all symptoms that may be associated with protein allergy. If your baby has one of these problems, call your pediatrician or family doctor, but never assume that the formula is causing the problem. Milk-protein allergy can be definitively diagnosed only by withdrawing the suspected offending protein, observing an improvement in the baby's condition, and then re-introducing the protein to the baby to observe the baby's response.
When I suspect protein allergy (either caused by cow milk or soy protein), I recommend a trial of a hydrolyzed protein formula. In these preparations, including Alimentum (Ross), Pregestimil (Mead Johnson) and Nutramigen (Mead Johnson), the protein (casein) has been broken-down into smaller units. The body's immune system doesn't recognize these smaller units as "foreign", so the allergic reaction stops. A positive response is usually noted within 3 to 4 days.
Another hypoallergenic (decreased tendency to provoke allergic reaction) product on the grocery shelves is Good Start (Carnation). The protein in this formula is a partial hydrolysate derived from the whey fraction of cow milk protein. This means that a portion of the cow milk protein in the formula are broken down, so the body is less likely to have an allergic reaction. Although some babies with protein intolerance may do well on this formula, I don't recommend Good Start as initial therapy for presumed protein allergy, since it does contain some intact (i.e. unhydrolyzed), and hence potentially allergenic, proteins.
Formulas For Special Needs
Aside from the products described above, numerous other infant formulas are available. Some of these are designed to treat specific inborn errors of metabolism, in which your baby is unable to utilize certain amino acids. Conditions requiring these formulas are usually diagnosed shortly after birth. Other formulas have been developed to meet the unique nutritional needs of premature infants.
Despite significant advances in infant formula design and manufacture, breast milk remains the optimal choice for infant nutrition. Nevertheless, these human milk substitutes provide nutrients sufficient to assure the normal growth and development of your baby.