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Is Breast Best?

Introduction

Since the advent of the Industrial Revolution and woman's entry into the work place, the presumed need for a substitute for human milk has spurred research on the development of the ideal formula. However, despite continued, improved modifications, cow's milk based formulas still do not exactly replicate the "gold standard" of human milk. The major macro- and micro-nutritional differences between whole cow's milk, infant formula, and human milk will be discussed, with particular emphasis on breast-feeding's infant immunological and neuro-developmental benefit, and positive health effects for the mother. It is important to understand that whilst breast milk remains best if not ideal in most circumstances, there are some contraindications to breastfeeding, and formula feeding may therefore occasionally be preferable.

A nutritional comparison of whole cow's milk based formula and human milk

The nutritional composition of human milk is species-specific and it varies interindividually (unique for each mother and child pair) and intraindividuality (with duration of lactation). Colostrum, the first milk produced after delivery, has a significantly different composition to that of mature human milk. For instance, colostrum has a much higher protein content than mature human milk, ( Emmett & Rogers 1997). This is crucial for providing a substantial initial dose of enzymes, which promote gut maturation, facilitate digestion and stimulate passage of the meconium, (Spencer 1996). Of equal importance are the high level of immunoglobins (Igs), particularly secretory IgA, which assist in protection against disease in a newborn infant's otherwise immature, immuno-compromised state. Certainly, human milk composition continues to change over time to match the infant's developmental needs, and despite the common misconception that mother's milk may be inadequate, it is almost always nutritionally sound regardless of dietary intake, (Barry Lawrence 1994). Infant formula cannot replicate such unique developmental-stage dependent changes in nutritional composition.

Macronutrients

Protein

Approximately two thirds of the protein in human milk are present in the acid-soluble component, whey, and the other one third in the acid-precipitate, casein, (Table 1). The ratio of whey to casein in cow's milk is a lot lower (20:80), resulting in a less digestible, tougher curd, (Emmett & Rogers ________________________________________________________________________________________________

Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

1997; Barry Lawrence 1994). The principle whey components differ for human milk (alphaLactalbumin, immunoglobins and others) and cow's milk/formula (beta-Lactalbumin), (Table 1), and beta-Lactalbumin is considered highly allergenic, (Redel & Shulman 1994). Additionally, human milk casein itself is softer and less compact, and therefore more readily digestible than cow's milk or formula curd. Human milk casein also readily forms stable aggregates with calcium and phosphorus, enhancing the level and bioavailability of these minerals in human milk, (Barry Lawrence 1994).

Table 1: Selected nutrient content of human milk, cow's milk based formula and cow's milk (per Litre). Adapted from Garrow, James and Ralph (2000)

Nutrient Energy (Kcal) Protein (g) Whey proteins: á -Lactalbumin â-Lactalbumin Total caseins Total Fat (g) Linoleic acid % total fatty acids (TFA) á -Linolenic acid % TFA Carbohydrates (g) Sodium (mmol) Potassium (mmol) Calcium (mmol) Phosphate (mmol) Iron (µmol) Vitamin C (mg) Vitamin D (µg)

1

Mature Human Milk 720 9.0 6.4 2-3 0.0 2-3 42 7.2 0.8 74 7 15 9 5 13 41 0.4

Infant formula1 Whole Cow's Milk 670 15 9.0 1.6 4.1 6.0 36 18.9 1.8 72 7 17 12 11 143 90 11 670 31 5.8 1.1 3.6 27 38 1.6 0.4 49 25 37 30 31 11 18 0.8

SMA Gold (SMA Nutrition), similar in nutrient composition to S26 (Wyeth) and Enfalac (Mead Johnson).

The total protein content of infant formula is slightly greater than that of human milk (Table 1). However, this does not provide the formula fed infant with an advantage, particularly because the type and quality of formula protein is poorer than that of human milk, with a distinctly difference amino acid profile, (Redel & Shulman 1994). For instance, carnitine (an essential protein required for infant metabolism of long-chain fatty acids) has been found at higher levels in breast-fed as compared with formula-fed infants, (Barry Lawrence 1994).

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

Moreover, the non-protein nitrogen content of human milk is greater (Table 1), and more diverse than infant formula. It includes: urea; uric acid; creatine; free amino acids, such as taurine and glutamic acid; amino sugars and alcohols; peptide hormones; nucleic acids and nucleotides. Some of these molecules are thought to be of developmental significance, and this is the reason for selective addition to infant formula, (Emmett & Rogers 1997). Taurine, an important neuronal and membrane component, is frequently added (formula examples include S26, SMA and Enfalac) and more recently and rarely, nucleotides are added (S26 Gold).

Carbohydrates

Lactose is the principal carbohydrate in human milk, and may assist in calcium absorption and the development of gut acidity, thus along with oligsosaccharides is influential in determining the nature of gut bacterial flora, (Barry Lawrence 1994). It is present in a greater concentration in human milk than infant formula, (Emmett & Rogers 1997).

Fat

Fat is the main source of energy in human milk, and is the most variable, within and between individuals, and in response to maternal nutrition, (Emmett & Rogers 1997). Infant formula fat level is based on the average total fat level of human milk (Table 1). However, the fat composition of human milk is distinct to that of cow's milk and formula, and consequently human milk fat is better absorbed. Human milk components lipase and L-carnitine (absent and of lower bioavailability, respectively in formula), also enhance the digestion, absorption and metabolism of human milk fat, (Redel & Shulman 1994; Emmett & Rogers 1997).

Of particular importance in human milk are the essential fatty acids, both linoleic (C18:2n6) and alpha-linolenic acid (C18:3n3), from which the long chain, polyunsaturated fatty acids (LC-PUFA), arachidonic acid (C20:4n6) and docosahexaenoic acid (C22:6n3) are respectively synthesised. LCPUFA have a variety of important roles in the infant. They are the precursors of essential metabolites such as prostacyclins and prostagalandins, are incorporated into the grey matter of the brain, and are also the major constituent of cell membrane phospholipids, (Emmett & Rogers 1997). Certainly, plasma and red blood cell membrane levels are higher in breastfed than formula fed infants and remain so throughout the first year of life (McVeagh 1994). Most infant formulae are still lacking or particularly low in the long chain PUFAs (S26 Gold is exceptional), and in general do not contain the full range of fatty acids found in human milk, (Emmett & Rogers 1997).

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

Micronutrients

In general, the high level of bioavailability of vitamins, minerals and trace elements, ensures that these components of breast milk are well utilised even when present at much lower concentrations than formula (Table 1), (Emmett & Rogers 1997). Iron, for instance is 49% bioavailable in human milk as compared with 4 % in formula, (Lawrence 1989 cited in Barry Lawrence 1994). However, supplementation may be necessary for vegan mothers (iron, calcium, B12), infants exposed to only low levels of sunlight (Vitamin D), and all infants require an initial dose of Vitamin K (administered either orally or via injection). Breast-fed babies also require iron supplementation at 6 months, usually achieved by supplementing breast-feeds with iron-enriched cereals, (Spencer 1996).

Nutritional Insufficiencies of Whole Cow's Milk

Infants fed whole cow's milk have insufficient intakes of iron, Vitamin E, and essential fatty acids (particularly linoleic acid), and excessive intakes of protein and electrolytes (Table 1), (American Academy of Pediatrics 1992). Deficiencies of iron in particular may be exaggerated by the high levels of calcium, phosphorous and low level of Vitamin C in cow's milk (Table 1), also reducing iron bioavailability from other dietary sources such as infant cereals (Emmett & Rogers 1997). Additionally, enteric blood loss is substantial in infants of greater than 6 months of age who are fed whole cow's milk (Ziegler et al 1990 cited in Spencer 1996), also contributing to iron loss.

Immunological Properties of Human Milk

Whilst essential components of host defence are present and functional at birth, they suffer from immaturities that put the newborn and especially the preterm infant at risk for disease and allergy, (Bernt & Walker 1999). Biochemically active components of human milk purported to have immunological properties are listed in Table 2. As indicated, these factors are thought to compensate for immature infant gastrointestinal (GI) and immunological function. It should be noted that heat treatment during formula manufacture denatures protective protein equivalents, negating their effect, and possibly increasing the allergenic potential, (Redel & Shulman 1994).

Breastfeeding as compared with infant formula feeding has indeed consistently been shown to reduce the incidence and/or severity of NEC, lower respiratory infection, otitis media, bacteremia, bacterial meningitis, botulism, and urinary tract infection, (Golding et al 1997; American Academy of Pediatrics 1997). There are also a limited number of studies that have shown a possible protective effect of human milk feeding against sudden infant death syndrome, Chron's disease, ulcerative colitis, lymphoma, allergic disease, insulin-dependent diabetes mellitus, and other chronic digestive diseases, (American Academy of Pediatrics 1997). ________________________________________________________________________________________________

Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

Neurodevelopmental Properties of Human Milk

In the last trimester of pregnancy and just after delivery, developing CNS requires supplies of certain LC-PUFAs (such as DHA) which the newborn is incapable of synthesising. Preterm infants fed on formula lacking LC-PUFA would seem to be particularly at risk, as brain growth is greatest during the last trimester of pregnancy. Indeed, long-term cognitive impairment has previously been found in premature infants tube-fed (regardless of mother's prior intent to breastfeed) exclusively on such formula as compared with those whose diet included human milk, amounting to a difference of 8.3 IQ points at age 7.5 to 8 years. This indicates a relationship between feeding method and

Table 2: Immaturities of the neonatal host defense and influence of biochemically active substances present in human milk (HM) on host defense function and maturation. Adapted from Bernt & Walker (1999), Lteif et. Al (1998), Emmett & Rogers (1997), Hamosh (1996) & Barry Lawrence (1994).

Infant immaturities Enhanced bacterial load through low: · · · · gastric acidity gastric, brush border & pancreatic enzymes peristalsis IgA, lysozyme Influence of HM Decreased bacterial load due to: · · · · peristalsis GI-enzymes gastric acidity immunologic factors Responsible HM Components GI hormones (GH), digestive enzymes, NK cells, macrophages, IgA, Lysozyme, Lactoferrin, Fibronectin Nucleotides, Growth Factors (EGF, IGF, TGF-á) Hormones (GH, cortisol) á-Lactalbumin, Lactoferrin, Cortisol, Bifidus factor Glycoconjugates

Enhanced permeability for macromolecules

Enhanced barrier function Enhanced barrier repair after disease

Adhesion pathogen on microvilli Adhesion non-pathogenic with immature glycosylation bacteria on enterocytes with pattern mature glycosylation pattern Adhesion pathogenic bacteria inhibited Impairment specific immunity · scarcity of submucosal B- and Tlymphocytes absense of secondary germal centres in Peyer's patches only IgM producing Bcells, absence of memory cells Development of & modulation of specific immunity (cell-mediated & humoral effects), Including: · B-cell stimulation by maternal Tlymphocytes

·

Igs Lymphocytes Cytokines Cortisol Nucleotides

·

1

SMA Gold (SMA Nutrition), similar in nutrient composition to S26 (Wyeth) & Enfalac (Mead Johnson).

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

developmental outcome beyond that attributable to genetic potential and parenting skills, (Lucas et. al 1990 cited in Campbell 1996).

Rapid brain growth continues throughout the early months of life, and cerebral DHA concentrations are also higher in term infants who are breastfed, and deficits in cognitive and neuroretinal development have been demonstrated in exclusively formula fed term infants. Moreover, some studies have demonstrated better visual evoked potentials in breastfed infants (Haller and Simpser 1999) and one study in three year old children showed the stereoacuity of those who had been breastfed was mature in 92% as compared with only 35% of their formula fed peers, ( McVeagh 1994).

Uncertainty regarding long-term congitive benefits of breast-feeding persists, due to significant methological flaws in the majority of studies and the "lag" effect. Current infant formula composition is significantly improved in nutritional quality as compared to formulas that today's teenagers consumed as infants, (Golding et al 1997).

Breastfeeding and Maternal Health

In addition to the benefits of breast-feeding to the infant, there are also a number of studies which indicate possible health benefits for mothers. Breastfeeding increases levels of oxytocin, resulting in less postpartum bleeding and more rapid uterine involution, and lactational amenorrhea causes less menstrual blood loss over the months after delivery. Recent research demonstrates that lactating women achieve an earlier return to prepregnant weight, delayed resumption of ovulation with increased child spacing, and improved bone remineralisition postpartum. Some studies have also shown a reduced risk of both ovarian cancer and premenopausal breast cancer, (American Academy of Pediatrics 1997).

Contraindications to Breastfeeding

There are situations in which breastfeeding may not be in the best interests of the infant. These include the infant who has galactosemia, the infant whose mother uses illegal drugs or particular medications (such as cancer chemotherapy agents), the infant who is exposed (through breastmilk) to high levels of environmental toxins (such as heavy metals), and the infant in the developed world whose mother has been infected with the human immunodeficiency virus (HIV), (Golding 1997; American Academy of Pediatrics 1997).

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

Summary

Whilst the nutritional value of infant formula continues to improve- with the recent addition of LCPUFA and nucleotides to some infant formula, in recognition of their developmental importancebreast-milk is still nutritionally superior in most instances. Current experimental evidence shows that breast-feeding certainly does enhance gastrointestinal and immunologic development and function, contributing to a reduction in the incidence of infant disease as compared with formula fed infants. There is some evidence to suggest that breast-feeding may also reduce the incidence of chronic degenerative disease, such as insulin dependent diabetes mellitus. Whilst the neurodevelopment of breastfed infants has been shown to be better than formula fed infants, today's infants fed with superior formula may not display similar cognitive deficits through childhood.

One wonders where the future of formula manufacture lies- in an attempt to replicate human milk, will human genes be cloned into cows for mass production of immunologically beneficial human proteins to later be added to formula? Irrespective of the future of formula feeding, at the present, the evidence suggests that despite the occasional need for nutritional supplementation and rare contraindications breast still remains the best, if not ideal infant mode of feeding!

References:

American Academy of Pediatrics, Committee on Nutrition, 1992, The Use of Whole Cow's Milk in Infancy, Pediatrics, Vol. 89, pp. 1105-1109. American Academy of Pediatrics, Work Group on Breastfeeding, 1997, Breastfeeding and the Use of Human Milk, Pediatrics, Vol. 100, pp. 1035-1039. Barry Lawrence P., 1994, Breast Milk: Best Source of Nutrition for Term and Preterm Infants, Pediatric Clinics of North America, vol. 41, pp. 925-941. Bernt K.M. and Walker W.A., 1999, Human milk as a carrier of biochemical messages, Acta Paediatrica, Suppl. 430, pp. 27-41. Carver J.D., 1999, Dietary nucleotides: effects on the immune and gastrointestinal systems, Acta Paediatrica, Suppl. 430, pp. 83-88. Campbell C., 1996, Breastfeeding and health in the Western World, British Journal of General Practice, Vol. 46, pp. 613-617. Copper G.V., Pierani P., Zampini L., Carloni I., Carlucci A., and Gabrielli O., 1999, Oligosaccharides in human milk during different phases of lactation, Acta Paediatrica, Suppl. 430, pp. 89-94. Emmett P.M. and Rogers I.S., 1997, Properties of human milk and their relationship with maternal nutrition, Early Human Development, vol. 49 Suppl., pp 7-28 Garrow J.S., James W.P.T and Ralph A., 2000, Human Nutrition and Dietetics (10th Ed.), Churchill Livingstone, UK., pp. 451 Golding J., 1997, Unnatural constituents of breast milk- medication, lifestyle, pollutants, viruses, Early Human Development, vol. 49 Suppl., pp. 29-43.

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

Golding J., Rogers I.S., Emmett P.M., 1997, Preface: Methology and summary of results, Early Human Development, vol. 49 Suppl., pp. 1-6 Haller C.A. and Simpser E., 1999, Breastfeeding: 1999 perspective, Current Opinion in Pediatrics, Vol. 11, pp. 379-383. Hamosh M., 1996, Breast-feeding: Unraveling the mysteries of Mother's Milk, Medscape Women's Health, Vol. 1, pp. 4 Kelleher D.K. and Duggan C, 1999, Breast milk and breastfeeding in the 1990s, Current Opinion in Pediatrics, Vol.11, pp. 275-280. Lteif A.N., Schwenk W. and Frederick W., 1998, Breast Milk: Revisited, Mayo Clinic Proceedings, Vol. 73, pp. 760-763. McVeagh P., 1994, Breast or bottle fed- what's the difference?, Modern Medicine, September Vol., pp. 78-87. Redel C.A. and Shulman R.J., 1994, Controversies in the composition of infant formulas, Pediatric Clinics of North America, vol. 41, pp. 909-931. Spencer J.P. 1996, Practical Nutrition for the Healthy Term Infant, American Family Physician, vol. 54, pp. 139144 Udall J.N and Suskind R.M., 1999, Cow's milk versus formula in older infants: consequences for human nutrition, Acta Paediatrica, Suppl. 430, pp. 61-67.

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Is Breast Best? Short Literature Review by Farrah Tate, 2000, for Masters Coursework. Grade: HD.

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