Nutritional balance studies of VLBW infants fed their mothers' milk fortified with a liquid human milk fortifier

Calcium, phosphorus and magnesium balance: FM 85 fortification of human milk does not meet mineral needs of extremely low birthweight infants

OBJECTIVE

Extremely low birthweight (<1000 g) infants are growing rapidly and their nutritional requirements for calcium, phosphorus, magnesium are high.

DESIGN

Prospective, mineral balance.

SETTING

The study was carried out at the Department of Neonatology, Virchow-Hospital, Charité Berlin and the Department of Molecular Trace Element Research, Hahn-Meitner-Institute Berlin.

SUBJECTS

Nineteen infants <1000 g birthweight were admitted, nine infants dropped out and 10 infants (birthweight 730-995 g), fed fortified human milk were included.

INTERVENTION

We collected infant's urine and feces for 72 h, a sample of human milk and infant's blood at 7 and 12 weeks of age. Elements were measured by inductively coupled plasma atomic emission spectrophotometry.

RESULTS

Mean (s.d.) mineral concentration in milk was low especially at 12 weeks: calcium 9.88 (+/-3.58) mmol/l, phosphorus 7.02 (+/-3.81) mmol/l, magnesium 1.59 (+/-0.54) mmol/l. Calcium retention was minimal or negative during the study, whereas phosphorus and magnesium balances were positive. Caffeine and diuretics increased mineral excretion. Serum alkaline phosphatase was mostly <800 U/l, and 162 U/l in one infant with zinc deficiency at 12 weeks. Alkaline phosphatase correlated with absorption and retention of phosphorus, and with longitudinal growth.

CONCLUSIONS

Infants <1000 g have high nutritional needs for calcium, phosphorus and magnesium, which are not met by a human milk fortifier widely used in Europe. Controlled trials are needed to assess requirements, duration and risks of mineral supplementation.

Nutrient accretion in preterm infants fed formula with different protein:energy ratios

BACKGROUND

Although standard formulas for preterm infants promote intrauterine rates of weight gain, fat deposition in preterm infants fed these formulas has been reported to be considerably higher than that in the fetus. We hypothesized that a preterm infant formula with a higher protein:energy (P:E) ratio would promote accretion rates of fat, fat-free mass, and minerals closer to those of the fetus.

METHODS

As part of a larger study to determine whether accretion rates of fat and fat-free mass closer to those of the fetus can be achieved with a higher P:E ratio, we present a descriptive analysis of 72-h nutrient balance studies performed on a subset (n = 15/30) of the infants randomly assigned to be fed formula with a P:E ratio of either 3.2 g/100 kcal or 2.6 g/100 kcal.

RESULTS

Despite the higher intake and net absorption of nitrogen by infants fed the higher P:E formula, there was no statistically significant difference in net nitrogen retention between groups. There also were no statistically significant differences between groups in digestible energy, metabolizable energy, energy expenditure, or energy storage. Thus, partitioning of stored energy as protein and fat did not differ between groups. The retention of calcium, phosphorus, sodium, potassium, copper, and zinc also did not differ between groups, and nitrogen intake did not affect mineral retention.

CONCLUSIONS

In this study, formula for preterm infants with a P:E ratio of 3.2 g/100 kcal vs. 2.6 g/100 kcal provided no apparent benefit in terms of the proportion of fat to lean tissue accretion as determined from nutrient balance data.

Calcium, phosphorus and magnesium needs for the low-birth-weight infant

Parental mineral-containing solutions for LBW infants should be started soon after birth. For the initiation of parenteral nutrition and during short-term therapy for less than 2 weeks' duration, LBW infants should receive parenteral nutrition solutions at rates of approximately 120-130 ml/kg/day, containing minerals at the following concentrations: Ca 15 mM, P 15 mM and Mg 2.5 mM. For optimal growth and nutrient utilization, however, LBW infants maintained on parenteral nutrition at rates of 120-130 ml/kg/day for 2 or more weeks should receive mineral concentrations of Ca 20 mM, P 20 mM and Mg 2.5 mM. In addition, these latter mixtures must contain amino acids in concentrations greater than or equal to 2.2 g% and cysteine-HCl must be provided. As newer formulations emerge, these recommendations may be modified. For human milk-fed LBW infants, after 1 week of enteral feeding, Ca and P should be supplied as fortifiers. Ca 2-3 mmol/kg/day and P 1.5-2.0 mmol/kg/day should be provided in addition to human milk. Magnesium supplementation of human milk is unnecessary. These recommendations assume that the intake of human milk is approximately 200 ml/kg/day and will decrease as more bioavailable mineral salts are found. For LBW infants fed commercial formula, the intake of Ca should be greater than 3.5 mmol/kg/day, P 2.5 mmol/kg/day and Mg 0.2 mmol/kg/day. These recommendations assume reported bioavailabilities of mineral salts. If more bioavailable sources are found, these recommendations will decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Human milk fortifiers

Unsupplemented human milk does not normally provide enough protein and minerals to secure optimal growth in low birthweight infants. We compared the growth and biochemical status of 21 very low birthweight infants, fed on their own mothers' fortified milk (seven infants) or a high-caloric-density formula (14 infants). The human milk fortifier is made from a mixture of cows' milk proteins (40% whey, 45% casein) and amino acids (15%) and has been demonstrated to be appropriate to achieve a plasma amino acid profile similar to that of normal infants fed exclusively on human milk. Infants receiving fortified human milk showed growth and biochemical profiles comparable to those receiving high-caloric-density formula. The supplementation that we describe here confirms the good results well documented by other authors. It is easy to perform and can be an acceptable alternative to the more sophisticated procedure of "lacto-engineering".

Protein quality of human milk fortifier in low birth weight infants: effects on growth and plasma amino acid profiles

Serum preprandial essential amino acid, urea and prealbumin concentrations, and growth rates were studied in appropriate for gestational age low birth weight infants fed one of three regimens: (1) human milk enriched with human milk protein (n = 17); (2) bovine whey protein hydrolysate (n = 18; and (3) a mixture of bovine proteins, peptides and amino acids designed to have an amino acid composition close to that of human milk proteins (n = 18). Energy and nitrogen intakes were similar in all groups. Growth rates and gross metabolic responses did not differ between the feeding groups. There were also no differences in the amino acid profiles between those infants fed human milk protein fortifier and mixed bovine protein fortifier. Infants fed the whey fortifier had significantly higher threonine concentrations in comparison to those fed exclusively human milk protein (287 +/- 63 mumol/l vs 168 +/- 26 mumol/l) whereas the levels of some other essential amino acids (i.e. valine, leucine, lysine, histidine, phenylalanine and tryptophan) were lower. The results indicate that growth rates and gross metabolic indices do not depend on the protein quality of human milk fortifiers. However, the addition of well balanced mixtures of bovine proteins to human milk results in amino acid profiles similar to those observed in LBW infants fed similar amounts of human milk proteins.

Nutrient needs of the preterm infant

Preterm infants exhibit special nutrient needs that differ substantially from other patient populations. Special characteristics include increased energy and protein requirements that must be addressed to prevent tissue catabolism and support growth. The immaturity of some organ systems may also complicate the administration of nutrition support. This article describes important characteristics of enteral and parenteral nutrition as it applies to the preterm infant.

Nitrogen and fat balances in very low birth weight infants fed human milk fortified with human milk or bovine milk protein

The study was designed to compare two different human milk fortifiers in a group of very low birth weight (VLBW) infants by analysing nitrogen and fat balances, serum concentrations of alpha-amino-nitrogen, urea, and prealbumin as well as growth rates when human milk enriched with one of the two studied fortifiers was fed to the infants. Fortifier A contained different bovine proteins, peptides and amino acids and had an amino acid composition comparable to that of the nutritional available proteins in human milk, with carbohydrates, and minerals. Fortifier B was composed of freeze-dried skimmed human milk and minerals to achieve a similar macronutrient composition in both fortifiers. Eleven infants were fed with human milk enriched with fortifier A and 13 with fortifier B. After a 10-day equilibration period, a 3-day metabolic balance was performed. On the 14th day of the study blood was obtained preprandially for serum analysis and growth rates were estimated. The nitrogen absorption rate (93.8% vs 93.5%) as well as the retention rate (80.8% vs 78.5%) were no different between the groups. The fat absorption rate (92.3% vs 91.5%) as well as the weight gain (32.1 vs 31.1 g/day) were similar and there were no differences in the serum parameters studied. The results indicate that feeding VLBW infants with human milk enriched with a well-balanced bovine fortifier fulfil their nutritional requirements as well as diets composed exclusively of human milk protein.

Mineral requirements of low-birth-weight infants

The minerals calcium (Ca), magnesium (Mg), and phosphorus (P) are essential for tissue structure and function. Recent studies have resulted in a more rational approach to the management of mineral intake in preterm infants receiving parenteral nutrition (PN) and enteral nutrition (EN). For preterm infants requiring PN, the use of PN solutions with a Ca content of 1.25-1.5 mmol/dl (50-60 mg/dl), a P content of 1.29-1.45 mmol/dl (40-45 mg/dl), and an Mg content of 0.2-0.3 mmol/dl (5-7 mg/dl) is supported by studies of mineral homeostasis with serial chemical and calciotropic hormone measurements, standard balance studies, and improved radiographic indices of bone mineralization. For infants requiring EN, an intake of approximately 4 mmol (200 mg) of Ca, 3.2 mmol (100 mg) of P, and 0.33 mmol (8 mg) of Mg/kg/day based on an average retention rate of 64% for Ca, 71% for P, and 50% for Mg should be sufficient to meet the requirements of preterm infants in early infancy. This level of intake is supported by data from balance studies using standard and stable isotope techniques, changes in bone mineral content (BMC) measurements, and calciotropic hormone data. Based on the timing of development of fractures and rickets, changes in BMC, and skeletal growth data, the increased Ca and P intake should continue for at least 3 months after birth or until reaching a body weight of about 3.5 kg. In addition, nonnutritional factors may have the potential to increase mineral loss and disturb mineral homeostasis; chronic diuretic therapy increases mineral loss, and aluminum contamination of nutrients theoretically may compound any skeletal disorder. Thus, attention to the level of mineral intake and factors important in mineral loss and mineral metabolism should optimize mineral retention in small preterm infants.