Association between proportion of milk feeds delivered via bottle at age 4 months and weight at 14 months – the Australian NOURISH trial

Introduction Several mechanisms have been proposed for the relationship between weight gain in infancy and obesity risk. While the link with formula intake and attendant higher protein intake is now well documented, it has been proposed that method of milk delivery may also contribute. While breastfeeding an infant largely has control over the amount of milk consumed, while when bottle feeding, either formula or expressed breastmilk, the care-giver can exert more control. Bottle-feeding practices that are not responsive to a child’s cues of hunger and satiety, may result in overfeeding excess weight gain. The aim of this analysis was to examine the relationship between proportion of milk feeds delivered via bottle (breastmilk, formula or mixed feeding) at age 4 months and weight-for age z-score (WAZ) at 14 months. Methods This is a secondary analysis of longitudinal data from mother-child dyads participating in the Australian NOURISH trial. Baseline assessment occurred when infants were approximately 4 months of age, at which time mothers reported three days of child dietary intake. For those infants who were exclusively milk-fed (breastmilk, formula or mixed feeding) over the three days, the average proportion of number of feeds delivered via a bottle per day was calculated; ranging from 0% for the exclusively breastfed infant fed directly from the breast, to 100% for the infant fed only via bottle. Anthropometry were measured by trained research staff at baseline and at a second assessment at child age 14 months and child WAZ (WHO Standards, 2008) and maternal BMI were derived. Multiple regression was used to determine the relationship between WAZ at 14 months and proportion of feeds delivered via bottle at 4 months of age adjusting for WAZ at baseline, protein intake, maternal BMI and age at child’s birth, and NOURISH trial allocation. Results Three days of dietary intake at 4 months and anthropometric data at 4 and 14 months was available for 284 infants (48% male). Mean proportion of feeds delivered via bottle per day at 4 months of age was 26% (sd= 39, range 0-100). The regression model explained 41% variance in WAZ at 14 months (adj R2=.41, SE=.66). WAZ at 14 months was associated with proportion of feeds delivered via bottle at 4 months of age (ß=.12, p=.01) adjusting for WAZ at 4 months (ß=.62, p<.001), protein intake, g/kg bodyweight per day (ß=.13, p=.02), maternal BMI (ß=.12, p=.01), maternal age (ß=-.05, p=.25) and NOURISH allocation (ß=-.08, p=.10). Conclusion These results add to the growing body of evidence that how an infant is fed - bottle feeding versus directly fed from the breast - may contribute to higher relative weight. Providing mothers with support to bottle feed in a way that is responsive to an infant’s hunger and satiety cues is a potential strategy for obesity prevention that requires further investigation.