Objective: To examine the association between timing of introduction of solid foods during infancy and obesity at 3 years of age.
Methods: We studied 847 children in Project Viva, a prospective pre-birth cohort study. The primary outcome was obesity at 3 years of age (BMI for age and gender ≥ 95th percentile). The primary exposure was the timing of introduction of solid foods, categorized as <4, 4 to 5, and ≥ 6 months. We ran separate logistic regression models for infants who were breastfed for at least 4 months ("breastfed") and infants who were never breastfed or stopped breastfeeding before the age of four months ("formula-fed"), adjusting for child and maternal characteristics, which included change in weight-for-age z score from 0 to 4 months-a marker of early infant growth.
Results: In the first 4 months of life, 568 infants (67%) were breastfed and 279 (32%) were formula-fed. At age 3 years, 75 children (9%) were obese. Among breastfed infants, the timing of solid food introduction was not associated with odds of obesity (odds ratio: 1.1 [95% confidence interval: 0.3-4.4]). Among formula-fed infants, introduction of solid foods before 4 months was associated with a sixfold increase in odds of obesity at age 3 years; the association was not explained by rapid early growth (odds ratio after adjustment: 6.3 [95% confidence interval: 2.3-6.9]).
Conclusions: Among formula-fed infants or infants weaned before the age of 4 months, introduction of solid foods before the age of 4 months was associated with increased odds of obesity at age 3 years.