Barriers and Facilitators to Cognitive Participation in Peer Support for Complementary Feeding in LMICs: A Theory‐Informed Systematic Review

ABSTRACT Suboptimal complementary feeding practices remain a significant challenge in LMICs. Peer support shows promise in improving these practices; however, their long‐term success hinges on sustained engagement and integration into existing support systems, aspects that remain poorly understood. This theory‐led systematic review aimed to understand why people participate, support, and continue using peer support for complementary feeding practices. The literature search covered studies conducted between January 1990 and February 2025. This pragmatic, Normalisation Process Theory‐led review employs an integrative mixed‐methods synthesis. We conducted a theory‐informed systematic review guided by the four subconstructs of cognitive participation, presenting the findings narratively into barriers and facilitators. While peer‐led complementary feeding promotion involves multiple actors at different levels, few studies directly included family members and caregivers beyond mothers, thereby limiting their cognitive participation. Most studies were donor‐driven. Financial, structural, sociocultural, training, and capacity‐related factors strongly influence peer‐led complementary feeding support. Their influences were not fixed; what served as facilitators in the initial stages of studies became barriers later, and vice versa. Household and local leaders and gatekeepers constrained peer support early in the interventions, but this later reversed with their involvement. Incentives boosted interest and increased enrolment. However, this also led to volunteers being less motivated and to attrition when resources were limited. Weak supportive supervision diminished the legitimacy of peer support, causing a loss of confidence in volunteers' skills. Keeping the momentum of early implementation stages requires a predictable funding model, primarily from domestic sources, and sustained engagement in the intervention. This can address multifaceted operational problems, ranging from recruitment to embedding the intervention in the health system. Political commitment, especially when translated into operational support, can strengthen the financial sustainability of peer support programmes.