American Journal of Clinical Nutrition, Vol. 77, No. 6, 1535S-1536S,
June 2003
© 2003 American Society for Clinical Nutrition
Preface
Bo Lönnerdal
Our knowledge of the composition of breast milk, how composition changes during lactation, and the nutritional and physiologic significance of the specific components is steadily increasing. It has also become increasingly accepted that, when infant formula is manufactured, the nutrient composition of breast milk cannot serve as a norm, because nutrients are utilized differently from formula. Rather, growth and clinical indexes of breastfed infants should be the guideline for formula-fed infants.
By invitation of the Mexican Pediatric Association (AMP) and the National Confederation of Mexican Pediatricians (CONAPEME), a group of scientists gathered at a symposium in Cancun, Mexico (May 23–24, 2002). The symposium was broadly titled "Innovaciones en Fórmulas Infantiles" (Innovations in Infant Formula) because the organizer recognized this as an area of special interest, but emphasis was placed on the numerous recent advances in research on breast milk, particularly the protein composition, and on clinical studies of breastfed and formula-fed infants. The speakers shared their knowledge regarding changes in infant formula that have occurred during the past decade, the increased understanding of the significance of individual proteins in breast milk, the revised estimated protein requirement of infants, and how the protein composition of infant formula may be modified to make it more similar to that of breast milk. Pediatricians and other health professionals from Mexico participated in the symposium. There was generous time for questions and answers, discussions, and sharing of clinical experiences.
Jane Carver (1) reviewed advances in formula composition that have been made during the past decade and their consequences for infants. Formulas have undergone several significant improvements, which include the addition of components such as long-chain polyunsaturated fatty acids (LC-PUFAs), nucleotides, and micronutrients, eg, selenium. The addition of LC-PUFAs was prompted by the finding of both arachidonic acid and docosahexaenoic acid in breast milk and research on their importance for infant development. Considerably higher concentrations of nucleotides were found in breast milk than in formula, and the addition of nucleotides to formula was shown to enhance immune function. Formulas were also found to contain considerably lower concentrations of selenium than does breast milk, and fortification of formulas with selenium resulted in blood and plasma selenium concentrations similar to those of breastfed infants. These topics were discussed primarily with regard to healthy term infants, but the special needs of postdischarge preterm infants were also considered.
Advances in our knowledge of individual proteins in breast milk and ongoing research on the physiologic significance of these proteins to breastfed infants were presented by Bo Lönnerdal (2). It is now recognized that some proteins in breast milk, notably secretory immunoglobulin A, lactoferrin, and 
1-antitrypsin, are relatively resistant to digestive enzymes and can exert their function in the gastrointestinal tract of breastfed infants. Other proteins, such as ß-casein and -lactalbumin, may be initially digested only in part, and smaller peptides formed during digestion may act locally in the small intestine. After exertion of their activities locally, these proteins may be completely broken down and used as a balanced source of amino acids in growing infants. Enhanced availability of pure breast-milk proteins by recombinant techniques and considerable progress in the development of test systems, such as human cells in culture and animal and nonhuman primate models, have made it possible to obtain a better understanding of the functions of several breast-milk proteins. These functions range from facilitating nutrient absorption, providing a defense against bacterial and viral infections, and stimulating mucosal development to enhancing the immune competence of breastfed infants.
It is generally believed that the amount and quality of protein provided by breast milk meets the protein and amino acid requirements of young infants. How much protein that is, how it changes during lactation, and, in particular, how it is "translated" into recommendations for formula-fed infants were topics discussed by Christophe Dupont (3). Early estimates of the protein content of human milk were vastly exaggerated. When safety margins were added to these overestimations, recommendations for the protein content of infant formula resulted in protein intakes of formula-fed infants that frequently were twice those of breastfed infants. With the realization that breast-milk protein concentrations had been overestimated and the observation that several metabolic indexes (blood urea nitrogen, plasma amino acid pattern) in formula-fed infants suggested excessive protein intake, steps have recently been taken to revise downward the estimated protein requirements during infancy and to issue more appropriate recommendations.
Concurrent with these discussions and revisions of recommendations, there has been a move by infant formula manufacturers to lower the protein content of their products. Eric Lien (4) presented the historical development of the protein content and composition of infant formula. Several clinical studies have shown that the protein concentration of infant formula can be safely reduced, resulting in metabolic indexes closer to those of breastfed infants, while maintaining adequate growth. This reduction has encompassed adjustments of the ratio of the major protein classes of cow milk, whey proteins and casein, so that the ratio in formula more resembles that of human milk (60:40) than the original 20:80 ratio of cow milk. By doing this, a plasma amino acid profile more similar to that of breastfed infants has been achieved. However, further research showed that the protein composition of human milk is different from that of cow milk; in particular, bovine whey proteins are different from human whey proteins. Therefore, there is a limit to what extent the protein composition of infant formula can be modified by simply altering the whey-to-casein ratio. Recently, advances in dairy technology have made it possible to obtain bovine whey fractions enriched in specific proteins. The use of these fractions in the production of infant formula modifies the protein and amino acid composition and brings formula another step closer to breast milk.
Improvements in protein composition will likely allow a further reduction in the protein content of infant formula, without resulting in a plasma amino acid pattern deviating substantially from that of breastfed infants. As it becomes technically possible to more closely approximate human milk protein quality, composition, and bioavailability, regulations governing infant formula nutrient requirements may need revision. Finally, all speakers emphasized that breast milk provides the optimum mode of feeding infants but expressed hope that new scientific and technologic advances can lead to improved formulas to the benefit of infants not being breastfed.
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ACKNOWLEDGMENTS
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I thank Wyeth Nutrition (Philadelphia) for supporting this meeting.
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REFERENCES
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- Carver JD. Advances in nutritional modifications of infant formulas. Am J Clin Nutr 2003;77(suppl):1550S–4S.[Abstract/Free Full Text]
- Lönnerdal B. Nutritional and physiologic significance of human milk proteins. Am J Clin Nutr 2003;77(suppl):1537S–43S.[Abstract/Free Full Text]
- Dupont C. Protein requirements during the first year of life. Am J Clin Nutr 2003;77(suppl):1544S–9S.[Abstract/Free Full Text]
- Lien EL. Infant formulas with increased concentrations of -lactalbumin. Am J Clin Nutr 2003;77(suppl):1555S–8S.[Abstract/Free Full Text]
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