Background: Infant feeding may play an important role in the development of childhood overweight and obesity.
Objective: The objective of this study was to examine whether duration of breastfeeding (BF), timing of introduction of complementary food, and protein intake at age 18 mo are associated with body mass index [BMI (measured in kg/m2)] and overweight at ages 7 and 11 y, independent of BMI during infancy.
Design: Children participating in the Danish National Birth Cohort were followed up at ages 7 and 11 y. Information on infant feeding, protein intake at age 18 mo, Ponderal Index at birth, child BMI (at ages 5 mo, 12 mo, 7 y, and 11 y), and several parental factors was available. Path analysis was used to assess the direct and indirect effects of infant feeding on BMI z scores (BMIz) at ages 7 (n = 36,481) and 11 y (n = 22,047). Logistic regression analyses were used to examine associations with overweight.
Results: Duration of BF was not associated with childhood BMIz at ages 7 and 11 y. Earlier introduction of complementary food (<4 mo old) was not associated with BMIz at age 7 y, but with a 0.069 (95% CI: 0.021, 0.117, P = 0.005) higher BMIz at age 11 y and increased risk of overweight at age 11 y (OR 1.44; 95% CI: 1.04, 2.00; P = 0.03). Protein intake from dairy products (per 5 g/d) was associated with higher BMIz only at age 7 y (OR: 0.012; 95% CI: 0.003, 0.021; P = 0.007). Protein intake from meat and fish (per 2 g/d) was associated with a 0.010 (95% CI: 0.004, 0.017; P = 0.003) higher BMIz at age 7 y, a 0.013 (95% CI: 0.005, 0.020; P = 0.002) higher BMIz at age 11 y and increased odds of overweight at age 7 y (OR: 1.07; 95% CI: 1.03, 1.10; P < 0.001), but not at age 11 y.
Conclusions: Intake of protein from meat and fish at age 18 mo was associated with higher BMIz and risk of overweight in childhood. However, the effect sizes were small. Early introduction of complementary food may be associated with child BMIz and child overweight. This study was registered at www.clinicaltrials.gov as NCT03334760.