Prolacta honors and values breastfeeding mothers and their committment to the health of babies
Clinically proven to improve health outcomes of critically ill preemies
Committed to scientific and clinical research in breast milk
Prolact Product Safety
baby_feeding_small

Variability in Nutritional Content of Breastmilk


Human milk composition is dynamic (Ballard & Morrow, 2013). The more that is learned about the composition of human milk the more it appears to be as much a bioactive substance, as it is a source of nutrition. While the innumerable immunologic benefits of human milk contribute to making it the best source of infant nutrition, the variability in its nutritional composition may necessitate implementation of strategies to optimize nutrient delivery to the newborn.

Human Milk Production and Composition

Lactogenesis, or the initiation of milk production occurs in three stages. In the first days after delivery, lactogenesis I occurs and colostrum is produced by alveolar secretory cells in the breast. Colostrum is a viscous, yellowish fluid, that has relatively high levels of immunoglobulin A, antibodies and lactoferrin which provide immune protection to the newborn.4 Colostrum contains oligosaccharides which play an important role in establishing the normal flora or microbiome of the infant’s gut.1 Anti-oxidants or carotenoids, necessary to neutralize the oxidative stress associated with delivery, are found in their highest levels in colostrum. The nutritional composition of colostrum demonstrates a higher concentration of protein due to a higher concentration of amino acids and an abundance of antibodies and lactoferrin. Lower levels of carbohydrate, fat and calories are present in colostrum than are in mature milk.4,5

Lactogenesis II presents by days 2 to 4 postpartum and is characterized by increased milk secretion as a mother’s “milk comes in”.1 Transition to mature milk occurs at approximately 7 days postpartum and is established by day 10.8 Milk supply is maintained through the combination of maternal hormone production and infant feeding practices. Complete emptying of the breasts, either by nursing or pumping stimulates increased milk production assuring adequate volume for the infant. During the transition to mature milk there is a decrease in the concentration of immunoglobulins, total protein, lactoferrin and anti-oxidants and an increase in the amount of carbohydrate, fat and calories.4

Variability of Human Milk

Human milk composition is dynamic.1 The nutritional components of human milk derive from three sources: some of the nutrients of milk originate by synthesis in the lactocyte or milk-producing structure in the breast, some are dietary in origin, and some originate in maternal body stores. The primary components of mature milk are water, carbohydrates, fats, proteins, vitamins, and minerals. The nutrient composition of human milk is remarkable for its variability (Schanler, 2012). The composition of human milk varies between women and for each woman secondary to gestation, stage of lactation, milk volume, time of day, frequency of feeding and within breastfeeding or milk expression (i.e., foremilk and hindmilk variations).

The major macronutrient in human milk is carbohydrate and the largest concentration is in the form of lactose. Lactose provides a major source of energy for the developing infant brain and accounts for approximately 40% of the total calories in human milk.1 Human milk lactose is easily digested and absorbed in the small bowel. The concentration of lactose in human milk is the least variable of the macronutrients though mothers who produce higher quantities of milk tend to have higher concentrations of lactose but a lower milk concentration of fat and protein.7

Fats are the second highest macronutrient concentration and accounts for 50% of total caloric intake. Much of the variation in macronutrient composition in human milk is a result of differences in fat content. Fats comprise approximately 4% of human milk and the major constituent of milk fat (98%) is in the form of triglycerides.8 Fat is the most highly variable macronutrient of milk. It has been suggested that hindmilk, or the latter portion of the feeding or pumping, may contain 2 to 3 times the concentration of milk fat found at the beginning of the feeding in the foremilk.9 Maternal nutrition and geographic location are known to affect the concentrations of long-chain polyunsaturated fatty acids (LCPUFAs) including arachidonic acid (AA) and docosahexaenoic acid (DHA) which play a significant role in neurodevelopment and vision.10

The protein components of human milk are critical for growth, development and immunoprotection. Milk proteins are divided into fractions of whey and casein. The concentrations of whey to casein in human milk are in a 60:40 ratio versus the 20:80 ratio found in bovine milk.4 Human milk has less total protein than bovine milk. Whey protein is more easily digested than casein, which requires greater energy expenditure to digest and forms tough rubbery curds. The protein content of milk obtained from mothers who deliver preterm is significantly higher than that of mothers who deliver at term. Protein levels decrease in human milk over the first 4 to 6 weeks of life regardless of timing of the delivery.1 Concentration of human milk protein is unaffected by maternal diet, but increases with maternal body weight for height, and decreases in mothers producing higher volumes of milk.7

Table by Nominee et al.

Table 1: “Standard” Milk Composition from Specified References

Macronutrient (g/dL) and Energy (kcal/dL) Composition of Human Milk*

Author/Year

n

Protein

Mean (±2 SD)

Fat

Mean (±2 SD)

Lactose

Mean (±2 SD)

Energy

Mean (±2 SD)

Term Reference Standard*

0.9

3.5

6.7

65 to 70

Term Infants: 24 hour collection, mature milk

Author/Year

n

Protein

Mean (±2 SD)

Fat

Mean (±2 SD)

Lactose

Mean (±2 SD)

Energy

Mean (±2 SD)

Nommsen et al2 (1991)

n=58

1.2 (0.9, 1.5)

3.6 (2.2, 5.0)

7.4 (7.2, 7.7)

70 (57, 83)

* Adapted from Pediatric Nutrition Handbook Sixth Edition AAP 2009.

Human Milk and the Preterm Infant

The benefits of human milk are such that the AAP breastfeeding policy further states that “all preterm infants should receive human milk,” either mother’s own milk, fresh or frozen as their primary diet and if mother’s own milk is unavailable, pasteurized human donor milk should be used. Fortification of expressed human milk is indicated by the policy for the infant born weighing less than 1.5 kg. to ensure adequate nutrient intake.1

Perhaps the greatest concern in providing human milk to premature infants is growth (Underwood, 2013). Premature infants have unique nutritional needs. Up to 17 weeks of their final growth occurs outside of the womb rather than intrauterine where nutrition is supplied by the placenta. This is the period when rapid, important growth and maturity of organ systems occurs. Fetal weight will double, length increase 25%, and 70% of every calorie is used for brain growth. Life in the extrauterine world requires increased caloric expenditure for thermal regulation, respiratory effort and growth. Protein content decreases over duration of lactation. Emerging evidence indicates that a higher protein intake is beneficial for growth of premature infants. 12 This necessitates clinical strategies for human milk fortification to manage the nutritional variability of human milk feedings.

johnson_chart
Schanler RJ & Oh W Composition of breastmilk obtained from mothers of premature infants as compared to breastmilk obtained from donors. J Pediatr 96:679 (1980).13
 

Underwood cautions against the use of “assumed” values in implementing strategies for fortification. “Assumed” values refer to a given nutritional value which may not be accurate because of variability in a mother’s own or donor milk and yet are used to calculate nutritional intake.11 An example of an “assumed” value would be that mother’s own milk or donor human milk contains 20kcal/oz. Unless the donor milk has been analyzed and standardized the clinician may overestimate the nutrition being provided.

Table 2: Differences in Donor Human Milk Samples from Published “Standard” Values

Macronutrient (g/dL) and Energy (kcal/dL) Composition of Human Milk*

Author/Year

n

Protein

Mean (±2 SD)

Fat

Mean (±2 SD)

Lactose

Mean (±2 SD)

Energy

Mean (±2 SD)

Term Reference Standard*

0.9

3.5

6.7

65 to 70

Donor Human Milk Samples

Author/Year

n

Protein

Mean (±2 SD)

Fat

Mean (±2 SD)

Lactose

Mean (±2 SD)

Energy

Mean (±2 SD)

Wojcik et al b(2009)

n=415

1.2 (0.7, 1.7)

3.2 (1.2, 5.2)

7.8 (6.0, 9.6)

65 (43, 87)

Michaelsen et al c (1990)

n=2553

0.9 (0.6, 1.4)

3.6 (1.8, 8.9)

7.2 (6.4, 7.6)

67 (50, 115)

Preterm Donor Milk

Landers & Hartmannd (2012)

n=47

1.4 (0.8, 1.9)

4.2 (2.4, 5.9)

6.7 (5.5, 7.9)

70 (53, 87)

* Adapted from Pediatric Nutrition Handbook Sixth Edition AMA 2009

An analysis of 415 samples of donor human breast milk collected sequentially from 273 donors demonstrated the potential error if the “assumed” value of 20kcal/oz is used.14 Analysis by a midrange infrared instrument measured that 25% of the donor milk samples had less than 17 kcal/oz, 35% were between 17.1-19.9 kcal/oz while only 30% of the samples were 20 kcal/oz or higher. The potential for such an error could occur when “assuming” values of many of the components in human milk resulting in a failure to meet nutritional targets for low birth weight infants.

A human milk caloric fortifier made by Prolacta Bioscience, Prolact CR™, is now commercially available to standardize human milk to help achieve a 20 Cal/fl. oz feeding solution before fortification when caloric content is measured to be less than the assumed 20 kcal/oz in either a mother’s own or donor human milk. This exclusively human, pasteurized fraction of milk cream contains no added minerals and is a viable method for boosting calories while maintaining the benefits and integrity of a 100% human milk diet.

Ziegler (2001) has advocated the practice of “individualized fortification” as the “best solution to the variability problem. The idea to analyze milk and to fortify it in such a way that each infant always receives the amount of nutrients that he or she needs is simple and very attractive.” He went on to comment that “The trouble is that implementation is very difficult.”15And it was very difficult in 2001.

The science of human milk nutrition and therapeutics is advancing at an incredible rate of speed. This fall saw the “1st International Conference of Human Milk Science and Innovation” convene in southern California. This meeting examined the emerging science and clinical use of human milk and human milk products. The rapid growth of human milk banks enables clinicians to provide donor milk for the preterm and low birth weight infant. Human donor milk can now be analyzed for accurate composition of nutrients providing for a “standardized” donor human milk product. Instruments that have the ability to analyze fat and protein in the Neonatal Intensive Care Unit (NICU) are in active development. These instruments will provide a means of lacto-engineering at the bedside while using micro-aliquots of milk for analysis. Such technology may ultimately support the delivery of milk “fractions” or “split products” i.e., protein, or fat, to individualize an infant’s nutritional plan day by day if not feeding by feeding.

References

(1) Ballard o & Morrow AL (2013). Human milk composition nutrients and bioactive factors. Pediatr Clin N Am 60 (2013) 49–74.
(2) Hanson, LA (2004). Immunobiology of human milk: how breastfeeding protects babies. Amarillo, TX: Pharmasoft Publishing.
(3) American Academy of Pediatrics. Breastfeeding and the use of human milk. Pediatrics 2012;129:3.
(4) Chertok IRA (2013).The postpartum period and lactation physiology. In Susan T Blackburn (Ed). Maternal, fetal, & neonatal physiology: A clinical perspective (4th ed.). Maryland Heights, MO: Elsevier.
(5) Zarban et al J Clin Biochem Nutr. 2009 September; 45(2): 150–154. Published online 2009 August 28. doi: 10.3164/jcn.08-233
(6) Schanler RJ (2012) Rationale for breastfeeding. In Patti J Thureen & William W Hay, Jr. (Eds). Neonatal Nutrition and Metabolism, (2nd ed.). New York: NY; Cambridge University Press.
(7) Nommsen LA, Lovelady CA, Heinig MJ, et al Determinants of energy, protein, lipid, and lactose concentrations in human milk during the first 12 mo of lactation: the DARLING Study. AM J Clin Nutr 1991;53(2):457-63.
(8) Lawrence RA & Lawrence RM (2011) Breastfeeding: A guide for the medical profession (7th ed.). Maryland Heights: MO; Elsevier. (9) Saarela T, Kokkonen J, Koivisto M. Macronutrient and energy contents of human milk fractions during the first six months of lactation. Acta Paediatr 2005;94(9):1176-81.
(10) Brenna JT, Varamini B, Jensen RG et al: Docosahexaenoic and arachidonic acid concentrations in human breast milk worldwide. American Journal of Clinical Nutrition 2007;85:6.
(11) Underwood MA Human milk for the premature infant. Pediatr Clin N Am 60 (2013) 189-207.
(12) Premji SS, Fenton TR, Sauve RS. Higher versus lower protein intake in formula-fed low birth weight infants. Cochrane Database Syst Rev 2006;(1):CD003959.
(13) Schanler RJ & Oh W Composition of breastmilk obtained from mothers of premature infants as compared to breastmilk obtained from donors. J Pediatr 96:679 (1980).
(14) Wojcik, KY, Rechtman, DJ, Lee, ML, et al Macronutrient analysis of a nationwide sample of donor breast milk. Journal of the American Dietetic Association. 2009;109:137-140.
(15) Ziegler EE. Breast milk fortification. Acta Paediatr 2001:90:720

Follow Us!