Randomized controlled trial of 4 compared with 6 mo of exclusive breastfeeding in Iceland: differences in breast-milk intake by stable-isotope probe.

Background: The WHO recommends exclusive breastfeeding (EBF) for 6 mo after birth. However, the time at which breast milk ceases to provide adequate energy and nutrition, requiring the introduction of complementary foods, remains unclear. Most studies that investigated this issue were observational and potentially confounded by variability in social circumstances or infant growth.

Objective: We hypothesized that EBF infants would consume more breast milk at age 6 mo than infants receiving breast milk and complementary foods.

Design: We measured anthropometric outcomes, body composition, and breast-milk intake at age 6 mo in infants who were randomly assigned at age 4 mo either to 6-mo EBF or to the introduction of complementary foods with continued breastfeeding. We recruited 119 infants from health centers in Reykjavik and neighboring municipalities in Iceland. In 100 infants who completed the protocol (50/group), breast-milk intake was measured by using stable isotopes, and complementary food intakes were weighed over 3 d in the complementary feeding (CF) group.

Results: Breast-milk intake was 83 g/d (95% CI: 19, 148 g/d) greater in EBF (mean ± SD: 901 ± 158 g/d) than in CF (818 ± 166 g/d) infants and was equivalent to 56 kcal/d; CF infants obtained 63 ± 52 kcal/d from complementary foods. Estimated total energy intakes were similar (EBF: 560 ± 98 kcal/d; CF: 571 ± 97 kcal/d). Secondary outcomes (anthropometric outcomes, body composition) did not differ significantly between groups.

Conclusions: On a group basis, EBF to age 6 mo did not compromise infant growth or body composition, and energy intake at age 6 mo was comparable to that in CF infants whose energy intake was not constrained by maternal breast-milk output.