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Quick GuideBaby Health: The Facts About Bottle Feeding
What is in an infant formula, and how do I choose the right one?
This article is designed to review the various types of infant formulas and the nutritional basis for choosing one formula type over another. This information can help "demystify" the myriad of choices available to a parent when considering options at the pharmacy or grocery store. A small percentage of newborn infants will require a specialized formula (for example, premature infants, infants with metabolic diseases, or infants with intestinal malformations). These children's unique dietary requirements should be an item of individual discussion between the parents and the infant's pediatrician and will not be addressed here.
In order to achieve appropriate growth and maintain good health, infant formulas must include proper amounts of water, carbohydrate, protein, fat, vitamins, and minerals. Each of these components is discussed below. The three major classes of infant formulas are
- milk-based formulas, which are prepared from cow milk with added vegetable oils, vitamins, minerals, and iron. These formulas are suitable for most healthy full-term infants and should be the feeding of choice when breastfeeding is not used, or is stopped before 1 year of age.
- soy-based formulas, which are made from soy protein with added vegetable oils (for fat calories) and corn syrup and/or sucrose (for carbohydrate). These formulas are suitable for infants who cannot tolerate the lactose (lactose intolerant, see below) in most milk-based formulas or who are allergic to the whole protein in cow milk and milk-based formulas. The American Academy of Pediatrics recommends the use of soy formulas for the above infants as well as for infants of parents seeking a vegetarian-based diet for a term infant. These formulas are not recommended for low-birth-weight or preterm infants or for the prevention of colic or allergies.
- special formulas for low-birth-weight (LBW) infants, low-sodium formulas for infants that need to restrict salt intake, and "predigested" protein formulas for infants who cannot tolerate or are allergic to the whole proteins (casein and whey) in cow milk and milk-based formulas
Water is an important part of a baby's diet because water makes up a large proportion of the baby's body. When properly prepared, all infant formulas are approximately 85% water.
Infant formulas are available in three forms: liquid ready-to-use, liquid concentrate, and powder concentrate. Liquid ready-to-use formulas do not require the addition of water, while the liquid and powder concentrates require the addition of water.
It is of prime importance for parents to read, understand, and follow the manufacturer's directions when adding water to liquid and powder concentrates. Adding too much water to these concentrates or adding water to ready-to-use formulas can lead to water intoxication in the baby. In severe cases, water intoxication can cause low blood sodium levels, irritability, coma, and even permanent brain damage. Conversely, failing to adequately dilute the concentrates with water causes formulas to be too concentrated, or "hypertonic." Hypertonic formulas can induce diarrhea and dehydration. In extreme cases, ingestion of overly hypertonic formulas can lead to kidney failure, gangrene of the legs, and coma. Therefore, parents should not adjust the amount of water that is added to concentrates to either "fatten the baby up" or "put the baby on a diet." Instead, parents should discuss their concerns regarding the baby's calorie intake with his/her pediatrician.
Carbohydrates (glucose, lactose, sucrose, galactose, etc.) are sugars or several sugars linked together. Carbohydrates provide energy (calories) for the brain tissues, muscles, and other organs. Lactose is a carbohydrate consisting of glucose linked to galactose. Lactose is the major carbohydrate in human breast milk, cow milk, and in most milk-based infant formulas.
While most infants will thrive on a formula that contains lactose, some infants are lactose intolerant. Lactose intolerance is due to a lactase enzyme deficiency (low levels of enzyme activity) in the small intestine. Lactase enzymes are necessary for "digesting" lactose by breaking the link between glucose and galactose. The intestines can then absorb the smaller glucose and galactose molecules. In infants who are lactase deficient, the undigested lactose cannot be absorbed. This, in turn, can cause diarrhea, cramps, bloating, vomiting, and gas. Lactase deficiency is more common in premature infants than in full-term babies. Lactase deficiency can also develop temporarily during recovery from viral gastroenteritis (commonly referred to as the "stomach flu"). Finally, lactase deficiency can be inherited (rarely).
For infants with lactose intolerance, formulas that contain no lactose can be used. Lactofree is an example of a milk-based formula that contains corn-syrup solids rather than lactose as its carbohydrate calorie source. Many soy-protein formulas also do not contain lactose and are suitable for lactose intolerant infants. In addition to corn-syrup solids, other examples of carbohydrates contained in lactose-free formulas include sucrose (table sugar), tapioca starch, modified cornstarch, and glucose polymers (short chains of glucose molecules).
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 and are not considered as a nutritional source and are not efficiently metabolized.) While formulas from different manufacturers may vary slightly in the relative proportion of these two proteins, healthy babies generally thrive on any milk-based formula brand.
Some 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 hypoallergenic (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.
Fat in human milk and formula provides a significant percentage of the total daily caloric needs for a growing infant. Formula manufacturers utilize many different vegetable oils for fat, including corn, soy, safflower, and coconut oils. Some formulas contain "predigested" fats known as medium chain triglycerides (MCT). These are analogous to the "predigested proteins" discussed above. Because of their unique application, formulas containing MCT are not routinely recommended for healthy infants and children.
There is a significant amount of research into determining the ideal concentration and ratios of fatty acids such as arachidonic acid (ARA) and docosahexanoic acid (DHA) for infant nutrition. Some studies have suggested that these may have a positive effect on short-term cognitive function and possibly early visual acuity. More research is needed to clarify this issue, and you should discuss this with your infant's pediatrician before supplementing.
Vitamins are organic substances that are essential in minute quantities for the proper growth, maintenance, and functioning of the baby. Vitamins must be obtained from food because the body cannot produce them. The exception is vitamin D, which can be produced by the skin when it is exposed to the sun. There are four fat-soluble vitamins (A, D, E, and K) and several water-soluble vitamins. These include the B vitamins, B1 (thiamine), B2 (riboflavin), B3 (niacin), B6 (pyridoxine), and B12 (cobalamin), as well as folate and vitamin C and pantothenic acid, and biotin. These vitamins have been added to infant formulas to ensure proper nutrition. Unless otherwise directed by their pediatricians, routine vitamin supplementation is not necessary for healthy full-term infants taking formulas.
High doses of certain vitamins can have adverse effects. For example, high doses of vitamin A can cause headaches, vomiting, liver damage, brain swelling, and bone abnormalities. High doses of vitamin D can lead to high levels of calcium in the blood and kidney and heart damage. Therefore, high doses of vitamins should not be given to infants and young children without supervision by their pediatricians.
Minerals (calcium, phosphorus, magnesium, iron, iodine, copper, and zinc) and trace elements (manganese, chromium, selenium, and molybdenum) are included in most formulas. Therefore, there is no evidence that mineral supplementation is necessary for healthy formula-fed, full-term infants.
Several years ago, it was recommended that infants from birth to 4 months of age receive a lower quantity of iron compared with those from 4 to 12 months of age. As such, several milk-based formulas such as Similac (Abbot Nutrition—formerly Ross) and Enfamil (Mead Johnson Pharmaceuticals) were marketed under two varieties—"low iron" and "high iron." Multiple studies on iron requirements for all infants have since been performed, and in 1999, the American Academy of Pediatrics (AAP) recommended against the use of any "low iron" formula for infants, due to the fact that these formulas are nutritionally deficient. Pediatricians currently recommend that all children receive the standard iron content found in most formulas. Both the FDA and the AAP have encouraged the infant-formula makers to discontinue production of "low iron" products, without success. This is due to the fact that many parents still purchase these because of a belief that iron in formula causes gastrointestinal side effects, including increased gas and constipation. Many studies have conclusively shown this not to be the case.