What is the optimal age for introduction of complementary foods?

In 2001, a WHO Expert Consultation concluded that waiting until 6 months to introduce complementary foods to breastfed infants confers several benefits for both infants and mothers. Nonetheless, there is still controversy about this issue. In developing countries, the reduced risk of infant gastrointestinal illness and increased duration of maternal lactational amenorrhea associated with exclusive breastfeeding for 6 months make the benefit-risk ratio of this recommendation highly favorable. In industrialized countries, the case is less clear-cut, but the benefit-risk ratio is also likely to be favorable with regard to infant infectious morbidity, motor development and maternal weight loss postpartum. For outcomes such as infant growth, food acceptance and iron or zinc status, the evidence for industrialized countries suggests no particular benefit but also very little risk of following this recommendation. Some exclusively breastfed infants may become iron- or zinc-deficient before 6 months, but this can be prevented more effectively by targeted iron and zinc supplementation to high-risk infants than by introducing complementary foods. On the whole, the evidence to date supports the WHO recommendation to introduce complementary foods at 6 months, but further research in industrialized countries would be useful.