This study was supported by funding from the National Institutes of Health (NIH) (Grant 1R15ES024520-01). The authors declare no conflict of interest.

Probiotics are commonly prescribed to promote a healthy gut microbiome in children. Our objective was to investigate the effects of probiotic supplementation on growth outcomes in children 0–59 months of age. We conducted a systematic review and meta-analysis which included randomized controlled trials (RCTs) that administered probiotics to children aged 0–59 months, with growth outcomes as a result. We completed a random-effects meta-analysis and calculated a pooled standardized mean difference (SMD) or relative risk (RR) and reported with a 95% confidence interval (CI). We included 79 RCTs, 54 from high-income countries (HIC), and 25 from low- and middle-income countries (LMIC). LMIC data showed that probiotics may have a small effect on weight (SMD: 0.26, 95% CI: 0.11–0.42, grade-certainty = low) and height (SMD 0.16, 95% CI: 0.06–0.25, grade-certainty = moderate). HIC data did not show any clinically meaningful effect on weight (SMD: 0.01, 95% CI: −0.04–0.05, grade-certainty = moderate), or height (SMD: −0.01, 95% CI: −0.06–0.04, grade-certainty = moderate). There was no evidence that probiotics affected the risk of adverse events. We conclude that in otherwise healthy children aged 0–59 months, probiotics may have a small but heterogenous effect on weight and height in LMIC but not in children from HIC.

Many infants do not receive breastmilk for the recommended 2-year duration. Instead, alternative milk beverages are often used, including infant formula and raw animal milk products. The purpose of this systematic review was to summarize the effect of animal milk consumption, compared to infant formula, on health outcomes in non-breastfed or mixed-fed infants aged 6–11 months. We searched multiple databases and followed Cochrane guidelines for conducting the review. The primary outcomes were anemia, gastrointestinal blood loss, weight-for-age, length-for-age, and weight-for-length. Nine studies were included: four randomized controlled trials (RCT) and five cohort studies. All studies, except one, were conducted in high income countries. There was a low certainty of evidence that cow’s milk increased the risk of anemia compared to formula milk (Cohort studies RR: 2.26, 95% CI: 1.15, 4.43, RCTs: RR: 4.03, 95% CI: 1.68, 9.65) and gastrointestinal blood loss (Cohort study RR: 1.52, 95% CI: 0.73, 3.16, RCTs: RR: 3.14, 95% CI: 0.98, 10.04). Additionally, there was low certainty evidence that animal milk consumption may not have a differential effect on weight and length-for-age compared to formula milk. Overall, the evidence was of low certainty and no solid conclusions can be drawn from this data. Further studies are needed from low- and middle-income countries to assess optimal milk type in non-breastfed infants aged 6–11 months.

IntroductionPrevalence rates of breastfeeding remain low even though the World Health Organization (WHO) and the American Academy of Pediatrics recommend exclusive breast feeding for the first 6 months of life in combination with appropriate complementary feeding beyond six 6 months of age. There have been several studies that address the implication of drinking animal milk and/or infant formula on children’s health and development when breast feeding is not offered during the first year of life. Vast improvements have been made in infant formula design, which may increase its benefits compared with animal’s milk. The objective of this review is therefore to synthesise the most recent evidence on the effects of the consumption of animal milk compared with infant formula in non-breastfed or mixed breastfed infants aged 6–11 months.Methods and analysisWe will conduct a systematic review and meta-analysis of studies that assessed the effect of animal milk compared with formula or mixed-fed (breastmilk and formula) on infants aged 6–11 months. The primary outcomes of interest include anaemia, gastrointestinal blood loss, weight for age, height for age and weight for height. We will include randomised and non-randomised studies with a control group. We will use the Cochrane risk of bias tools to assess the risk of bias. We will use meta-analysis to pool findings if the identified studies are conceptually homogenous and data are available from more than one study. We will assess the overall quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation approach.Ethics and disseminationThis is a systematic review, so no patients will be directly involved in the design or development of this study. The findings from this systematic review will be disseminated to relevant patient populations and caregivers and will guide the WHO’s recommendations on formula consumption versus animal milk in infants aged 6–11 months.Trial registration numberCRD42020210925.

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