Eleven RCTs were included in the review (n=1,459 infants); nine were rated as being of good quality (scoring 3 or more out of 5). Sample size ranged from 34 to 297 infants. There was no indication of publication bias.
Stool colonisation with bifidobacteria and/or lactobacilli: Nine trials evaluated this outcome, but meta-analysis was not possible due to significant heterogeneity in the methods used to measure and report colony counts. Six trials reported significantly higher levels of bifidobacteria following prebiotic supplementation; the remaining three trials found no significant differences. Two of three trials reporting on lactobacilli counts reported higher levels in the supplemented group.
Stool colonisation with pathogenic bacteria: Six trials reported mixed results on this outcome, but no meta-analysis was possible.
Stool pH: Eight trials reported on this outcome. Six trials were pooled in a meta-analysis and found a significant reduction in stool pH for children receiving prebiotic supplementation (WMD -0.65, 95% CI -0.76 to -0.54). Significant heterogeneity was noted for this outcome (I2=81%).
Stool consistency: Five trials that assessed this outcome, reported that stools were softer in the prebiotic-supplemented group.
Stool frequency: Three trials reported a higher frequency of stools in prebiotic-supplemented infants.
Physical growth in first year of life: Nine trials reported this outcome. The four trials that were pooled showed that infants receiving supplemented milk formula had better weight gain (WMD 1.07g, 95% CI 0.14 to 1.99).
Tolerance: Seven of eight trials that reported various indicators of tolerance found that prebiotic supplementation was well tolerated. Symptoms evaluated included excessive irritability, crying, regurgitation and vomiting. The one trial that reported some problems with tolerance assessed two different strengths of two different prebiotics; more tolerance problems appeared to occur in the higher strength supplementation group.