Implementation Determinants and System-Level Barriers in Supplementary Feeding Programs for Children Under Five in Low- and Middle-Income Countries: A Critical Narrative Review

Background: Supplementary feeding programs are widely used to prevent or manage child undernutrition, but their population-level benefit depends on implementation. Objective: To critically synthesize multilevel determinants of program reach, continuity, utilization, equity and sustainability in low- and middle-income countries (LMICs). Methods: We conducted a critical narrative review of peer-reviewed and grey literature identified through iterative database searching and targeted verification. Sources were charted by setting, design, program, implementation determinant, consequence, evidence directness, limitation and narrative credibility. Direct, related and indirect evidence were weighted differently in the synthesis. Results: Direct and related evidence most consistently linked program performance to financing and supply continuity, workforce preparation and supervision, food acceptability, caregiver understanding, equitable access and monitoring linked to corrective action. Direct evidence was concentrated in South Asia and selected programs in Indonesia, Iran and Ethiopia. Evidence concerning digital delivery, father-inclusive approaches, community-health-worker incentives and donor transition was largely indirect and supports hypotheses rather than established program effects. Conclusions: Reliable delivery systems and effective child-level utilization are necessary for supplementary feeding programs to contribute to nutritional outcomes. Recommendations supported mainly by indirect evidence require prospective evaluation in supplementary feeding settings, particularly in underrepresented LMIC regions.