There are too few infants studied to be certain that adverse effects of protein supplementation are not increased. Blood urea levels are increased (WMD 1.0 mmol/l, 95% CI 0.8 to 1.2 mmol/l).
However, the role of human milk in preterm infants is less well defined. The nutrient content of preterm human milk provides insufficient quantities of protein, sodium, phosphate and calcium to meet the estimated needs of the infant. In addition, large fluid volumes may be required to provide sufficient calories to maintain adequate growth.
There is evidence that preterm infants require higher protein intakes than term infants to attain adequate growth rates, and have relatively higher protein turnover rates (Hay 1994). Preterm infants fed human milk alone show slower growth than those fed a preterm infant formula containing supplemental protein (Bishop 1996; Lucas 1984; Lucas 1986; Lucas 1989; Lucas 1990a; Lucas 1990b; Lucas 1990c; Lucas 1994; Lucas 1994b). Declining serum albumin and blood urea concentrations in these infants suggest that inadequate protein intakes may be at least partly responsible for these changes. It is not clear to what extent the better neurodevelopmental outcomes reported in babies receiving preterm formula may be attributable to their higher protein intakes.
In contrast, excessive protein intakes have been reported to result in adverse neurodevelopmental outcomes, and to be associated with evidence of metabolic stress such as acidosis and elevated blood urea concentrations (Goldman 1969).
For a detailed discussion of the suitability of human milk for low-birthweight infants, see Schanler 1995.
This review updates the existing review of Protein supplementation of
human milk for promoting growth in preterm infants which was published
in The Cochrane Library, Issue 3, 1999 (Kuschel
1999). This update adds additional data from one previously included
trial (Polberger 1989).
A subgroup analysis was planned to evaluate differences in outcomes between supplementation with bovine milk protein and human milk protein.
2. Secondary outcomes
a. Nitrogen retention
b. Serum albumin concentrations
c. Adverse effects
Gastrointestinal disturbance
Feeding intolerance
Diarrhea
Necrotizing enterocolitis (NEC)
Metabolic acidosis
Blood urea
Search keywords included 'Infant,-Newborn', 'Dietary Protein', and 'Milk,-Human', including all subheadings for each term.
Additional information was requested from the authors of each trial to clarify methodology and results as necessary.
Each author extracted the data separately, compared data, and resolved differences.
The standard method of the Neonatal Review Group was used to synthesize the data. Results were expressed as relative risk and weighted mean difference.
Human milk protein supplements were used by three studies (Rönnholm 1982, Boehm 1988, Polberger 1989) and bovine casein hydrolysate by one (Putet 1987). Protein intakes approximated 1.5g/kg/day across all studies. Fluid intakes between studies ranged from approximately 164 to 200 ml/kg/day. The duration of intervention and the study period is not clear for three studies (Boehm 1988, Putet 1987, and Rönnholm 1982). Polberger 1989 ceased supplementation when infants were breast fed or reached a weight of 2200g.
Rönnholm 1982 provided supplemental calcium to the control group because of concerns that ultrafiltration of human milk inadvertently provided more calcium to the protein-supplemented group. Polberger 1989 supplemented all infants with calcium and phosphorus. Calcium and phosphorus supplementation in the other two studies is unknown. Rönnholm 1982 and Polberger 1989 provided supplemental vitamins.
Studies that were excluded from the review are listed in the Table 'Characteristics of Excluded Studies'. Beaufrere 1990 conducted a non-randomized study of protein supplementation. Moro 1991, Moro 1995, and Boehm 1990 did not use an unsupplemented control group. There was insufficient information in the report of the study by Minoli 1988 to include the results in this analysis and no further information could be obtained.
Additional information was provided by Professor NCR Räihä (co-author of Polberger 1989, Boehm 1988, and Minoli 1988), Dr S Polberger (Polberger 1989), and Professor G Putet (Putet 1987, Beaufrere 1990).
Polberger 1989 withdrew two of nine infants randomized to the protein supplementation group (feed intolerance, need for parenteral nutrition) and one of eight infants randomized to the unsupplemented group (apnea). Rönnholm 1982 does not report results for ten infants randomized and then withdrawn, and group allocation is not able to be determined.
Polberger 1989 used a regression of growth parameters against time to calculate a measure of growth. The slope of the regression was converted to units of g/kg/day and cm/week for the study period.
Short Term Growth Parameters
All studies evaluated short term growth over the course of the intervention.
Supplementation with protein resulted in an average increase in weight
gain of 3.6 g/kg/day (95% CI 2.4 to 4.8 g/kg/day). Linear growth increased
in infants receiving protein supplementation (WMD 0.28 cm/week, 95% CI
0.18 to 0.38 cm/week), as did head growth (WMD 0.15 cm/week, 95% CI 0.06
to 0.23 cm/week).
Long Term Growth Parameters
No study evaluated long term growth.
Neurodevelopmental Outcomes
No study evaluated long term neurodevelopmental outcomes.
Nitrogen Retention
No study evaluated this outcome.
Serum Albumin Concentrations
Only one study (Polberger 1989) evaluated
serum albumin concentrations. There were no significant differences between
the groups (29.5 vs. 27.0 g/l for protein-supplemented and unsupplemented
infants, respectively - additional information provided by Dr S.Polberger).
Putet
1987 found elevated total serum protein values (49.9 vs. 44.1 g/l,
p<0.05) in supplemented infants. Rönnholm
1982 demonstrated elevated total plasma amino acid levels in supplemented
infants (2339 vs. 1447 umol/l at 8 weeks of age, p<0.001).
Feeding Intolerance
Polberger 1989 withdrew one infant assigned
supplemental protein.
Diarrhea
No study evaluated this outcome.
Necrotizing Enterocolitis
Polberger 1989, with results reported
for only 7 infants in each group, stated that no infant developed NEC.
Metabolic Acidosis
Rönnholm 1982 found that blood pH
was significantly lower in supplemented infants at 2 weeks of age (pH 7.32
vs. 7.37, p<0.05, no standard deviation data provided) but there were
no differences at subsequent intervals. Putet 1987
did not demonstrate any significant difference in bicarbonate levels between
the groups (23.2 vs. 21.1 mmol/l).
Blood Urea
Three studies (Boehm 1988, Polberger
1989, Putet 1987) showed increased urea levels
in supplemented infants (WMD 1.0 mmol/l, 95% CI 0.8 to 1.2). Rönnholm
1982 did not provide absolute values but similarly noted higher urea
levels in supplemented infants. The clinical significance of this is unclear
as the higher levels in the supplemented group were not outside a range
considered normal.
Although the differences for these short term growth outcomes are small, the effect is cumulative. For prolonged hospital stays, a small advantage in weight gain or head or linear growth may have a significant impact on growth parameters at discharge or even age at discharge. These outcomes were not able to be evaluated in this review. Protein supplementation may also result in increased serum protein levels.
There is no information available evaluating the pre-specified long term growth and neurodevelopmental outcomes.
Urea levels are higher in infants receiving protein supplementation, but the clinical significance of this is not clear and elevated values may reflect adequate (rather than excessive) dietary protein intake. There are insufficient data to evaluate other potential adverse effects.
| Study | Methods | Participants | Interventions | Outcomes | Notes | Allocation |
| Boehm 1988 | Randomized study
Single center Randomization method: Unknown Blinding of randomization: Can't tell Blinding of intervention: Can't tell Complete follow-up: Yes Blinding of outcome measure: Can't tell |
9 treatment, 7 control infants entered trial. Preterm infants (VLBW
<1500g and LBW >1500g).
Feeding on day 1, full feeds by one week of life. Mean final feeding volume approximately 200ml/kg/day. Exclusions: major clinical illness. |
Lyophilized human milk protein (approximately 1.5g/kg/day) supplementation
of maternal or donor preterm human milk (9 infants) vs. unsupplemented
human milk (7 infants).
Not stated when intervention ceased. |
Short term growth parameters
Blood urea levels |
Only the VLBW arm of the study has been included in the overview, as this is consistent with the other studies in this review. | B |
| Polberger 1989 | Randomized study
Single center Randomization method: Sealed envelopes Blinding of intervention: Double blind Complete follow-up: No Blinding of outcome measure: Adequate |
9 treatment, 8 control infants entered trial.
Preterm infants <1500g, appropriate for gestational age Enteral feeds tolerated at 170ml/kg/day Exclusions: major illness or abnormality, oxygen dependency |
1.0g human milk protein (lyophilized) per 100ml human (unpasteurized
maternal or unpasteurized term banked donor) milk vs. unsupplemented milk.
Intervention ceased at approximately 2200g or when breast fed. All infants were supplemented with additional vitamins, calcium lactate (30mg/kg/day) and sodium phosphate (20mg/kg/day). From 4 weeks, 2mg/kg/day elemental iron was given to all infants. |
Short term growth parameters
Plasma amino acids and proteins Urine amino acids |
This study had four arms - unsupplemented vs. supplemented with protein
vs. supplemented with fat vs. supplemented with fat and protein. The analyses
of the fat and combined fat and protein arms are discussed in other reviews
on fat and multicomponent fortification respectively.
34 infants were enrolled in all four study arms - 6 were withdrawn following randomization (1 control, 2 protein, 1 fat, 2 fat and protein) and 7 infants were left in each arm. The infants in the treatment group were smaller than those of the control group at outset, and received more days of the intervention, and were heavier at study completion. There were large fluctuations in the energy intake for all four groups across the study. |
A |
| Putet 1987 | Quasi-randomized study. First infant randomized, second infant "matched"
Single center Randomization method: Unknown Blinding of randomization: Can't tell Complete follow-up: Yes Blinding of outcome measure: Can't tell |
8 treatment, 8 control infants entered trial. VLBW male infants.
Medically well, oral feeds started 24-48 hours after birth Intakes 164(+/-7) and 172(+/-11) ml/kg/day for the treatment and control groups, respectively. |
Casein hydrolysate (1g per 100ml) added to pooled human milk (8 infants) vs unsupplemented human milk (8 infants). Duration of intervention not clear. | Short term growth parameters
Plasma amino acid levels. Blood urea and protein levels. Acid-base studies. |
B | |
| Rönnholm 1982 | Quasi-randomized
Single center Randomization method: Alternate allocation Complete follow-up: No Blinding of outcome measure: No |
Uncertain number of treatment and control infants entered trial (see
Notes). Preterm, <1520g
Enrolled at 2 days if free of major illness and major malformation |
0.8g human milk protein per 100ml human milk (pasteurized maternal
or term donor milk) vs. unsupplemented human milk.
Target fluid volume 200ml/kg/day. All infants reecived supplemental vitamins (although some infants in different doses, as part of another study). Control infants received calcium supplements (10mg/kg/day). It is not clear when the intervention was ceased. |
Short term growth parameters
Serum albumin and protein levels Amino acid profiles Hemoglobin levels (not analysed in this review) |
54 infants were initially enrolled. 10 infants were excluded post-randomization
for medical reasons or insufficient enteral feeding (group allocation unclear).
Two infants who developed hydrocephalus were excluded from head circumference
measurements.
Half the infants in each group received (randomly) supplementation with fat (MCT oil, 1.0g/100ml of milk). The authors state that fat supplementation did not affect outcomes and therefore grouped the infants according to protein supplementation. Data is not extractable for protein supplementation alone vs. unsupplemented milk alone. Despite addition of protein to dietary intakes, there was no difference in energy intakes between the protein supplemented and unsupplemented groups. |
D |
| Study | Reason for exclusion |
| Beaufrere 1990 | Not randomized. |
| Boehm 1990 | Comparison of two forms of protein supplementation which did not include an unsupplemented control group. |
| Minoli 1988 | Unable to obtain sufficient data from published abstract and communication with author. |
| Moro 1991 | Comparison of human milk protein versus bovine milk protein. No unsupplemented control group. |
| Moro 1995 | No control group receiving unsupplemented human milk. |
Boehm G, Müller DM, Beyreiss K, Räihä NCR. Evidence of functional immaturity of the ornithine-urea cycle in very-low-birthweight infants. Biol Neonate 1988;54:121-125.
Polberger 1989 {published and unpublished data}
* Polberger SKT, Axelsson IA, Räihä NCE. Growth of very low birth weight infants on varying amounts of human milk protein. Pediatr Res 1989;25:414-419.
Polberger SKT, Axelsson IE, Räihä NCR. Amino acid concentrations in plasma and urine in very low birth weight infants fed protein-unenriched or human milk protein-enriched human milk. Pediatrics 1990;86:909-915.
Polberger SKT, Fex GA, Axelsson IE, Räihä NCR. Eleven plasma proteins as indicators of protein nutritional status in very low birth weight infants. Pediatrics 1990;86:916-921.
Putet 1987 {published and unpublished data}
Putet G, Rigo J, Salle B, Senterre J. Supplementation of pooled human milk with casein hydolysate: energy and nitrogen balance and weight gain composition in very low birth weight infants. Pediatr Res 1987;21:458-461.
Rönnholm 1982 {published data only}
Rönnholm KAR, Sipila O, Siimes MA. Human milk protein supplementation for the prevention of hypoproteinemia without metabolic imbalance in breast milk-fed, very low-birth-weight infants. J Pediatr 1982;101:243-247.
Rönnholm KAR, Siimes MA. Haemoglobin concentration depends on protein intake in small preterm infants fed human milk. Arch Dis Child 1985;60:99-104.
Rönnholm KAR, Simell O, Siimes MA. Human milk protein and medium-chain triglyceride oil supplementation of human milk: plasma amino acids in very low-birth-weight infants. Pediatrics 1984;74:792-799.
* Rönnholm KAR, Perheentupa J, Siimes MA. Supplementation with human milk protein improves growth of small premature infants fed human milk. Pediatrics 1986;77:649-653.
Beaufrere B, Putet G, Pachiaudi C, Salle B. Whole body protein turnover measured with 13C-leucine and energy expenditure in preterm infants. Pediatr Res 1990;8:147-152.
Boehm 1990 {published data only}
Boehm G, Melichar V, Senger H, Müller D, Räihä NCR. Effects of varying energy intakes on nitrogen retention and growth in very low birthweight infants fed fortified human milk. Acta Paediatr Scand 1990;79:228-229.
Minoli 1988 {published data only}
Minoli I, Moro G, Fulconis, Räihä N. Growth and protein metabolism in VLBW infants fed with human milk formula: a reference model. 11th European Congress of Perinatal Medicine. Abstract 4102. Rome, Italy, April 10-13, 1988.
Moro 1991 {published data only}
Moro GE, Minoli I, Fulconis F, Clementi M, Räihä NCR. Growth and metabolic responses in low-birth-weight infants fed human milk fortified with human milk protein or with a bovine milk protein preparation. J Pediatr Gastroenterol Nutr 1991;13:150-154.
Moro 1995 {published data only}
Moro GE, Minoli I, Ostrom M, Jacobs JR, Picone TA, Räihä NCR, Ziegler EE. Fortification of human milk: evaluation of a novel fortification scheme and of a new fortifier. J Pediatr Gastroenterol Nutr 1995;20:162-172.
* indicates the primary reference for the study
Bishop NJ, Dahlenburg SL, Fewtrell MS, Morley R, Lucas A. Early diet of preterm infants and bone mineralization at age five years. Acta Paediatr 1996;85:230-236.
Goldman HI, Freudenthal R, Holland B, Karelitz S. Clinical effects of two different levels of protein intake on low-birth-weight infants. J Pediatr 1974;85:764-769.
Hay WW Jr. Nutritional requirements of extremely low birthweight infants. Acta Paediatr Suppl 1994;402:94-99.
Lucas A, Gore SM, Cole TJ et al. Multicentre trial on feeding low birthweight infants: effects of diet on early growth. Arch Dis Child 1984;59:722-730.
Lucas A, Baker BA. Breast milk jaundice in premature infants. Arch Dis Child 1986;61:1063-1067.
Lucas A, Morley R, Cole TJ et al. Early diet in preterm infants and developmental status in infancy. Arch Dis Child 1989;64:1570-1578.
Lucas A, Brooke OG, Morley R, Cole TJ, Bamford MF. Early diet of preterm infants and development of allergic or atopic disease: randomised prospective study. BMJ 1990;300:837-840.
Lucas A, Cole TJ. Breast milk and neonatal necrotising enterocolitis. Lancet 1990;336:1519-1523.
Lucas A, Morley R, Cole TJ, et al. Early diet in preterm babies and developmental status at 18 months. Lancet 1990;335:1477-1481.
Lucas A, Morley R, Cole TJ, Gore SM. A randomised multicentre study of human milk versus formula and later development in preterm infants. Arch Dis Child 1994;70:F141-F146.
Lucas A, Morley R. Does early nutrition in infants born before term programme later blood pressure. BMJ 1994;309:304-308.
Schanler RJ. Suitability of human milk for the low-birthweight infant. Clin Perinatol 1995;22:207-222.
Kuschel CA, Harding JE. Protein supplementation of human milk for promoting growth in preterm infants. In: The Cochrane Library, Issue 3, 1999. Oxford: Update Software.