Abstract: We included 32 studies (21 RCTs and 11 CBAs); 26 of these (16 RCTs and 10 CBAs) were in meta-analyses. More than 50% of the RCTs were judged to have low risk of bias for random selection and incomplete outcome assessment. We judged most RCTS to be unclear for allocation concealment, blinding of outcome assessment, and selective outcome reporting. Because children and parents knew that they were given food, we judged blinding of participants and personnel to be at high risk for all studies. Growth. Supplementary feeding had positive effects on growth in low- and middle-income countries. Meta-analysis of the RCTs showed that supplemented children gained an average of 0.12 kg more than controls over six months (95% confidence interval (CI) 0.05 to 0.18, 9 trials, 1057 participants, moderate quality evidence). In the CBAs, the effect was similar; 0.24 kg over a year (95% CI 0.09 to 0.39, 1784 participants, very low quality evidence). In high-income countries, one RCT found no difference in weight, but in a CBA with 116 Aboriginal children in Australia, the effect on weight was 0.95 kg (95% CI 0.58 to 1.33). For height, meta-analysis of nine RCTs revealed that supplemented children grew an average of 0.27 cm more over six months than those who were not supplemented (95% CI 0.07 to 0.48, 1463 participants, moderate quality evidence). Meta-analysis of seven CBAs showed no evidence of an effect (mean difference (MD) 0.52 cm, 95% CI -0.07 to 1.10, 7 trials, 1782 participants, very low quality evidence). Meta-analyses of the RCTs demonstrated benefits for weight-for-age z-scores (WAZ) (MD 0.15, 95% CI 0.05 to 0.24, 8 trials, 1565 participants, moderate quality evidence), and height-for-age z-scores (HAZ) (MD 0.15, 95% CI 0.06 to 0.24, 9 trials, 4638 participants, moderate quality evidence), but not for weight-for-height z-scores MD 0.10 (95% CI -0.02 to 0.22, 7 trials, 4176 participants, moderate quality evidence). Meta-analyses of the CBAs showed no effects on WAZ, HAZ, or WHZ (very low quality evidence). We found moderate positive effects for haemoglobin (SMD 0.49, 95% CI 0.07 to 0.91, 5 trials, 300 participants) in a meta-analysis of the RCTs. Psychosocial outcomes. Eight RCTs in low- and middle-income countries assessed psychosocial outcomes. Our meta-analysis of two studies showed moderate positive effects of feeding on psychomotor development (SMD 0.41, 95% CI 0.10 to 0.72, 178 participants). The evidence of effects on cognitive development was sparse and mixed. We found evidence of substantial leakage. When feeding was given at home, children benefited from only 36% of the energy in the supplement. However, when the supplementary food was given in day cares or feeding centres, there was less leakage; children took in 85% of the energy provided in the supplement. Supplementary food was generally more effective for younger children (less than two years of age) and for those who were poorer/ less well-nourished. Results for sex were equivocal. Our results also suggested that feeding programmes which were given in day-care/feeding centres and those which provided a moderate-to-high proportion of the recommended daily intake (% RDI) for energy were more effective. Feeding programmes for young children in low- and middle-income countries can work, but good implementation is key.

Plain-language summary: We included 32 studies; 21 randomised controlled trials (in which children were randomly assigned to receive either supplementary feeding (intervention group) or not (a control group), and 11 controlled before-and-after studies (in which outcomes were observed before and after treatment in a group of children who were not randomly assigned to an intervention and a control group). The number of children in them ranged from 30 to 3166. Most studies were from low- and middle-income countries; three were from high-income countries. We found that, in low- and middle-income countries, providing additional food to children aged three months to five years led to small gains in weight (0.24 kg a year in both RCTs and CBAs) and height (0.54 cm a year in RCTs only; no evidence of an effect in other study designs),and moderate increases in haemoglobin. We also found positive impacts on psychomotor development (skills that involve mental and muscular activity). We found mixed evidence on effects of supplementary feeding on mental development. In high-income countries, two studies found no benefits for growth. The one effective study involved Aboriginal children. We found that food was often redistributed ('leakage') within the family; when feeding was home-delivered, children benefited from only 36% of the energy given in the supplement. However, when the supplementary food was given in day care centres or feeding centres, there was much less leakage; children took in 85% of the energy provided in the supplement. When we looked at different groups supplementary food was more effective for younger children (under two years old) and for those who were poorer or less well-nourished. Results for sex were mixed. Feeding programmes that were well-supervised and those that provided a greater proportion of required daily food for energy were generally more effective. We judged evidence from the RCTs to be of moderate quality and evidence from the CBAs to be of low quality.