Complementary feeding and micronutrient status: a systematic review.

Systematic review of studies in generally healthy, full-term infants and toddlers, mainly from developed or high-HDI countries. Included populations were breastfed, formula-fed, or mixed-fed infants, with complementary feeding comparisons made across randomized and nonrandomized studies.

This systematic review evaluated complementary feeding strategies in infancy, including earlier versus later introduction of complementary foods and beverages and different complementary-food compositions. The active regimens of interest were iron-containing foods such as meats and iron-fortified cereals, zinc-containing fortified cereals, and foods with different fatty-acid profiles, compared with standard or lower-iron complementary feeding.

Overall, iron-containing complementary foods helped maintain iron status or prevent iron deficiency in the first year among infants at risk of low iron intake, while benefit was less clear for infants with adequate iron stores. Moderate evidence also supported zinc-containing complementary foods for zinc status and complementary foods with different fatty-acid profiles for fatty-acid status. Across timing studies, introducing complementary foods at 4 months versus 6 months showed no long-term advantage or disadvantage for iron status in healthy full-term infants. Evidence for vitamin D, vitamin B-12, and folate status was insufficient or limited.

The evidence base was heterogeneous in interventions, outcomes, and reporting, with many studies providing incomplete arm-level dosing or demographic detail. Sample sizes were often modest, follow-up was limited in many trials, and most data came from high-income settings, which reduces generalizability. Evidence for several micronutrients was sparse, and some findings were inconsistent across studies and time points.