The Association Between the Early Introduction of Solid Food and Childhood Obesity Risk: A Systematic Review.

The purpose of this systematic review was to evaluate the association between the timing of solid food introduction during infancy and the risk of childhood obesity. The review specifically examined whether early introduction (before four months of age) is linked with increased risk of overweight or obesity in childhood. We conducted a systematic search of five major databases (PubMed/MEDLINE, Embase, Web of Science, Cochrane Library, and Google Scholar) from inception to January 15, 2025. Eligible studies included observational cohort, cross-sectional, quasi-experimental, and case-control studies that assessed the relationship between the timing of solid food introduction and childhood obesity outcomes. Two independent reviewers screened articles, extracted data, and assessed study quality using appropriate tools (ROBINS-I tool (Risk Of Bias In Non-randomized Studies of Interventions), AXIS, or the Newcastle-Ottawa Scale (NOS). Due to heterogeneity in study design, population, and outcome definitions, a narrative synthesis was conducted instead of meta-analysis.  Seventeen studies met the inclusion criteria out of 1,402 screened records. Most studies found that the introduction of solid foods before four months of age was associated with increased risk of childhood obesity or higher BMI z-scores. This association was more prominent in formula-fed infants. However, variation in study design, exposure classification, and measurement outcomes limited comparability. Risk of bias across studies ranged from moderate to serious, primarily due to confounding and reliance on parental recall. Early introduction of solid foods (before four months) appears to be associated with increased childhood obesity risk, particularly in the absence of breastfeeding. Nevertheless, due to variability and methodological limitations across studies, findings should be interpreted with caution. Further high-quality prospective studies using standardized outcome measures are warranted. The review protocol is registered in PROSPERO (CRD42025640375).