**Background:** Despite global progress, child malnutrition persists in parts of Africa, and engaging men in maternal, infant, and young child nutrition (MIYCN) is increasingly recognized as important for improving child health and challenging harmful gender norms. However, evidence on effective strategies to reach men and barriers to their participation is limited. This study evaluated the impact of two behaviour change interventions—mobile text messaging (SMS) and interpersonal communication (IPC), alone and in combination—on men's MIYCN knowledge in rural Tanzania, and explored barriers to male engagement.
**Methods:** The study was a 2×2 factorial, cluster-randomized controlled trial (cRCT) conducted in Mtwara, a rural region in southern Tanzania with poor child nutrition indicators (e.g., only 19.9% of children 6–23 months consume minimal meal frequency vs. 39.9% nationally; stunting 37.7% vs. 34.4% nationally). Forty dispensary catchment areas (DCAs) with >3000 residents were stratified by population size and randomly allocated to four arms: (1) SMS only, (2) IPC only, (3) SMS+IPC, and (4) control (usual care). Primary participants were pregnant women and mothers of children <12 months; male household members were also enrolled. The IPC intervention consisted of monthly group discussions and bi-monthly home visits by community health workers (CHWs) using the government's *Mkoba wa Siku 1000* programme. The SMS intervention used the *Wazazi Nipendeni* service, sending life stage-timed health and nutrition messages (average 4.9 messages/month during pregnancy and first year, declining to 1.25/month by child's fifth year). Data were collected at baseline (March–April 2018) and endline (July–September 2019) from 1394 men (1442 at baseline, 394 lost to follow-up, 347 new men added at endline). Men's knowledge was assessed via 14 multiple-choice questions covering breastfeeding, child feeding/micronutrients, and hygiene. A process evaluation partway through the intervention (April 2019) included focus group discussions (FGDs) and in-depth interviews (IDIs) with men from active and inactive villages. Quantitative data were analyzed using mixed-effects linear regression models adjusting for clustering and baseline differences (religion, drinking water source, toilet type, garden ownership). Qualitative data were analyzed using content analysis in ATLAS.ti.
**Key Results:** Baseline characteristics were generally similar across arms, though some differences existed (e.g., religion, wealth, food security). Intervention exposure: Among men with mobile phone access (82.4%–91.1%), 43.4% in SMS and 35.9% in SMS+IPC reported receiving health/nutrition SMS in the past 2 years vs. 12.8% in control and 13.3% in IPC. IPC meeting participation was 21.9% in IPC-only vs. 43.8% in SMS+IPC; home visits were reported by 41.4% in IPC-only and 55.9% in SMS+IPC. No men in control or SMS-only reported IPC exposure. Knowledge scores: At baseline, scores were comparable across arms. At endline, all intervention groups showed significant improvements in total knowledge compared to control. The adjusted total knowledge score increase was 0.030 points for SMS (p=0.02), 0.039 for IPC (p=0.04), and 0.066 for SMS+IPC (p<0.001). For child feeding/micronutrients, increases were 0.048 (IPC, p=0.03) and 0.090 (SMS+IPC, p<0.001); for hygiene, increases were 0.052 (SMS, p=0.02), 0.065 (IPC, p=0.001), and 0.073 (SMS+IPC, p<0.001). Breastfeeding knowledge did not differ significantly from control. The combined SMS+IPC group consistently showed the largest effects. Qualitative findings: Men who attended IPC meetings viewed them positively, citing learning about child health, practical skills (e.g., peanut porridge, hand-washing stations), and appreciating CHW expertise. However, 44.0% of non-attendees cited lack of interest, often due to perceptions that nutrition is women's work. Logistical barriers included inconvenient meeting location (42.1%) and timing (16.5%), and economic priorities (14.1% cited work conflicts). Some men felt CHWs directed information only to women. Recommendations included practical demonstrations, integrating topics like agriculture and finance, better timing (e.g., Friday mornings), using village leaders for publicity, and offering incentives.
**Clinical Implications:** This study demonstrates that a combined SMS+IPC intervention can significantly improve men's MIYCN knowledge in a low-resource setting, with the largest effects in the combined arm. However, low male participation in IPC activities highlights persistent gender norms and logistical barriers. To achieve meaningful male engagement, interventions may need to incorporate gender-transformative approaches (e.g., community champions, joint couple trainings), address economic constraints by linking nutrition to livelihoods, and use male CHWs or respected community leaders to recruit men. The findings support the potential of mobile messaging as a scalable tool to reach men, but suggest that additional strategies are needed to shift norms and sustain participation.