Original ArticlesThe Impact of Timing of Introduction of Solids on Infant Body Mass Index

ObjectivesTo evaluate the associations between breastfeeding duration, age at solids introduction, and their interaction in relation to infant (age 9-15 months) above normal body mass index (BMI).Study designCross-sectional, population-based study with 3153 infants from Melbourne (2007-2011). Above normal BMI (z score > 2, equivalent to >97.7th percentile) defined using the World Health Organization standard.ResultsBoth longer duration of full and any (full or partial) breastfeeding were associated with lower odds of above normal BMI (eg, aOR, 0.37 [95% CI, 0.22-0.60] for full breastfeeding 4-5 months versus 0-1 months). Compared with introduction of solids at 5-6 months, both early and delayed introduction were associated with increased odds of above normal BMI (aOR for 4 months, 1.75 [95% CI, 1.10-2.80] and for ≥7 months, 2.64 [95% CI, 1.26-5.54] versus 6 months). Such associations differ by breastfeeding status at 4 months (interaction P = .08). Early introduction of solids was associated with increased odds of above normal BMI in both infants fully or partially breastfed for ≥4 months (aOR, 3.66; 95% CI, 1.41-9.51) and those breastfed for <4 months (aOR, 3.11; 95% CI, 1.39-6.97). Introduction of solids at ≥7 months was associated with increased odds of above normal BMI (aOR, 5.79; 95% CI, 1.91-17.49) among infants breastfed for <4 months only.ConclusionIntroduction of solids at 5-6 months, compared with either early or delayed introduction, is associated with decreased odds of above normal BMI at 1 year of age, regardless of infants' breastfeeding status at 4 months. These results may have implications for public health guidelines with regard to recommendations about the optimal timing of the introduction of solid foods in infancy.