Infant Formulas Versus Breast Milk
  
     

Author: W. Steven Pray, Ph.D., R.Ph., Professor, Pharmaceutics, School of Pharmacy, Southwestern Oklahoma State University, Weatherford, OK 

Summary

When breast-feeding is not an option, a variety of infant formulas provide babies adequate nutrition. [U.S. Pharmacist 22(11), 1997. © 1997 Jobson Publishing Corp.] 

Introduction

Infant formulas have a difficult gap to fill. They must mimic breast milk as closely as possible. Yet it is difficult to produce a formula equal in all respects to breast milk, because its exact chemical composition is not yet known.[1,2] 

Infant nutrition is also complicated by the fact that newborns do not have equal food requirements. Their nutritional needs are affected by gestational age, birth weight and growth rate. For these reasons, infant formulas are a compromise between the ideal infant nutrition and starvation. Nevertheless, they do meet the needs of most babies adequately, allowing them to thrive. In fact, formula-fed infants are often heavier than their age-matched breast-fed counterparts, having more adipose tissue.[3] 

Mothers may not breast-feed for numerous reasons, such as previous difficulty with breast-feeding, knowing someone who had difficulties, perceived nipple anomalies (inverted nipples), or previous breast reduction or augmentation surgery.[4] Even the mother who intends to breast-feed may be dissuaded by incidents such as embarrassment during early attempts or lack of the milk ejection (let-down) reflex. This reflex, which moves milk to the areolae, is inhibited by pain, anxiety, stress or smoking and may cause the mother to abandon her efforts to breast-feed. Currently, only 54% of U.S. babies are breast-fed; the rest are fed infant formulas. 

Fat

While many adults concerned with reducing their cholesterol levels avoid foods high in saturated fat, infants need fat in their diet. Because infants can only ingest a certain amount of fluid each day,[1] the fluid must contain the maximal amount of nutrients per milliliter. 

Fat yields the highest number of calories (more than double those of carbohydrates and protein). For this reason over half of the calories in breast milk and formulas are derived from fat. Both breast milk and formulas contain 20 calories per ounce[5] and 30 grams of fat per liter. Formulas add fat in the form of palm, coconut, corn, soy or safflower oils.[2] 

Protein

Protein is the most important factor in ensuring proper growth and development of the infant.[6] Most infant formulas contain 15 g/L of protein (human milk contains 10 - 12 g/L during early lactation and 9 - 12 g/L in later lactation).[2,7] Cow's milk is higher in phenylalanine and tyrosine but lower in taurine and cysteine. For this reason, cysteine and taurine are often added to formulas. The infant cannot convert cysteine and methionine to taurine, which may be active in neurotransmission, growth modulation and membrane stabilization. 

A major controversy in the comparison of formula to breast milk concerns the type of protein used, quantified as the whey-casein ratio.[2] Human milk protein is composed of 65% whey and 35% casein. Whey from human milk contains such vital substances as alpha-lactalbumin, lactoferrin, immunoglobulins, albumin, enzymes (e.g., lysozyme), growth factors, and hormones. In contrast, cow's milk contains only 18% whey versus 82% casein. Cow's milk whey contains beta-globulin of unknown function and secondary proteins which are denatured during commercial heat processing. Thus, their immunologic value is negated while their allergenicity is increased. These differences notwithstanding, formulas predominating in either whey or casein had equal effect on infants in terms of fat and carbohydrate intake, weight, height, length, head circumference and skin-fold measurements. 

Carbohydrate

Carbohydrate in the form of lactose accounts for 40% of the energy intake of breast milk and cow's milk-based formulas.[8] The major problem with carbohydrate in infant formula is with lactose intolerance, in which case lactose-free soy-based formulas or lactose-free cow's milk-based formulas may be used. The carbohydrates present in soy-based formulas include sucrose, glucose polymers (e.g., corn syrup solids) or cornstarch, which are easily absorbed by the lactose-intolerant baby. Premature infants are also relatively lactase deficient. Glucose polymers added to the premature infant formula help compensate for this inability to fully utilize lactose as a nutrient source.[2] 

Vitamins and Minerals

FDA regulations specify nutrient levels for infant formulas. To be approved, formulas must contain a host of vitamins and minerals, as well as trace elements (e.g., zinc, manganese, copper, iodine) and electrolytes. Vitamin K is added in higher levels than in breast milk, to reduce the risk of hemorrhagic disease of the newborn. A female whose diet is inadequate may produce breast milk poor in pyridoxine, cyanocobalamin, and folic acid. Strict vegetarians who breast-feed and do not take supplemental cyanocobalamin produce milk that contains little or none of this vitamin. If a mother's breast milk is deficient in any vitamins or minerals, the physician should recommend dietary supplements for the baby. Alternatively, the mother may choose to feed the baby an infant formula that contains all the vitamins and minerals necessary to prevent deficiencies. 

The main area of controversy involves the iron content of infant formulas. For reasons unclear to researchers, infants absorb 100% of the iron in breast milk (less than 1 mg/L), but cannot absorb all of the iron in infant formulas. Most infant formulas contain approximately 12 mg/L of iron, which usually allows for adequate iron uptake. However, some parents attribute symptoms such as abdominal discomfort, constipation, diarrhea, colic and irritability to iron intolerance. In response, manufacturers have marketed low-iron formulas containing only 2 mg/L of iron. The low-iron formulas may alleviate these symptoms, but they cannot maintain proper hemoglobin status and should be avoided.[1,5] Iron deficiency can result in anorexia, failure to thrive, delayed development of the immune system, and impaired psychomotor and mental development.[9 ] 

Cow's Milk Allergy

Infants are particularly susceptible to developing an allergy to food proteins, perhaps because the infant gut is more permeable to macromolecules.[10] Allergy to cow's milk is a good example. In most cases the allergy develops during the first few months of life. Cow's milk allergy is an immunologically mediated allergic reaction to certain proteins in cow's milk.[10] The most common sources of allergic reaction are bovine serum albumin, beta-lactoglobulin, alpha-lactalbumin, casein, bovine immunoglobulin, and lactoferrin. The incidence of cow's milk allergy is 1% - 8%,[11] and may occur as a result of the following: 
Antigens in the mother's breast milk. 


Feeding milk, eggs, or cereal to the infant prior to the age of 6 months, including exposure to cow's milk from an alternate caregiver (e.g., the babysitter). 


Allowing a "taste" of ice cream, which delivers 1,000 times more antigen than that found in human milk.[12] 
At some time during the first year of life, the affected infant will experience symptoms such as diarrhea and vomiting occurring within one hour of feeding. Mucus in the stools, abdominal pain and excessive gas also occur. Other symptoms include respiratory (stridor, wheezing, rhinitis, cough), central nervous system (irritability), and dermatological manifestations (e.g., urticaria, atopic dermatitis).[9] Approximately 50% - 60% of infants will exhibit gastrointestinal symptoms, 20% - 30% will have respiratory involvement, and 50% - 70% will develop dermatological symptoms.[10] An infant with cow's milk allergy must not ingest cow's milk due to a risk of anaphylaxis. 

While soy protein- based formulas are a possible option for a baby with cow's milk allergy, 17% - 47% will also react to soy protein.[10] Protein hydrolysates (extensively hydrolyzed protein) are less allergenic, but the infant may not like their taste.[13] Further, their new protein structures created by the enzymes may provoke an allergic response.[14] 

Although goat's milk might appear to be a viable alternative, its proteins are cross-reactive with those in cow's milk, thus it should be avoided. It is also deficient in several vitamins. 

The prognosis for babies with cow's milk allergy is encouraging. After one year, 50% will no longer be allergic.[10] The figure rises to 75% in two years and 90% in three years. Fewer than 1% of babies will carry a lifelong allergy to cow's milk. 

When to Stop Infant Formula

The baby's first birthday is a good time to stop giving infant formula.[1] Whole milk rather than skim or low-fat milk must be given to fulfill the child's requirement for fat and allow normal development of the brain and central nervous system. Evaporated milk is nutritionally inadequate and should be avoided. Special products formulated for toddlers are not necessary, according to a leading physician authority on children's nutrition. 

Breast Milk: Imitated But Not Duplicated

Breast milk is ideally suited for the average infant, delivering all needed nutrients. It is a species-specific liquid containing unique substances such as living cells (e.g., macrophages), hormones, antibodies, active enzymes (which promote gut maturation, facilitate digestion and stimulate passage of meconium) and other proteins (e.g., immunoglobulins such as IgA) that cannot be artificially supplied to the infant.[5] Breast milk composition varies on a diurnal basis, and its fat content changes according to the time of the feeding episode ("fore" milk versus "hind" milk).[3] Early milk (colostrum) contains proportionally greater amounts of protein and minerals and less fat than mature milk. These ratios reverse as the infant ages. 

The U.S. Public Health Service has set a goal for the year 2000 to have 75% of babies breast-feeding at the time of hospital discharge. This goal has produced initiatives to increase the propensity to breast-feed.[5,15] 

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