The Intervention Nurses Start Infants Growing on Healthy Trajectories (INSIGHT) responsive parenting intervention for firstborns affects dietary intake of secondborn infants

Background: Although previous work has shown that children with older siblings tend to have poorer diet quality, no study has directly compared diets of infant siblings. Objective: The goals of this analysis were to examine birth-order differences in dietary intake between firstborn (FB) and secondborn (SB) siblings, and to determine whether a responsive parenting (RP) intervention modified birth-order effects on diet. Methods: The Intervention Nurses Start Infants Growing on Healthy Trajectories (INSIGHT) study randomly assigned first-time mothers to an RP intervention, which included guidance on feeding, sleep, soothing, and interactive play, or control. INSIGHT mothers who delivered a second child enrolled in an observation-only study of their SB infant (SIBSIGHT). Mothers completed FFQs for both children at ages 6 (n = 97 sibling pairs) and 12 (n = 100) mo. FB compared with SB intake of food groups of interest were compared, and the moderating effect of the RP intervention on birth-order differences was tested using generalized linear mixed models. Results: Though FBs and SBs had similar diets, more FBs than SBs consumed 100% fruit juice at both 6 (13.8 compared with 3.2%, P = 0.006) and 12 mo (46.0 compared with 32.0%, P = 0.01). SBs consumed fruit more frequently (FB 2.8 compared with SB 3.2 times/d, P = 0.01), and were more likely to consume fried potatoes (FB 38.4 compared with SB 57.6%, P = 0.0009) and processed meats (FB 43.0 compared with SB 58.0%, P = 0.02) than FBs at 12 mo. There were no differences by birth order in intake of sweets, snacks, or sugar-sweetened beverages at 12 mo. At 12 mo, RP-group SBs ate vegetables more times per day (3.2) than control SBs (2.2, P = 0.01). RP-SBs also consumed a greater variety of vegetables (10.2) than control-SBs (7.9, P = 0.01). Conclusions: Birth order is not consistently associated with healthy or unhealthy infant dietary intake. However, an RP intervention delivered to first-time mothers may benefit subsequent infants' vegetable intake.