The Intervention Nurses Start Infants Growing on Healthy Trajectories (INSIGHT) Responsive Parenting Intervention for Firstborns Affects Dietary Intake of Secondborn Infants

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.

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.

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.

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).

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. This trial was registered at clinicaltrials.gov as NCT01167270.