Objective: To better understand the mechanisms behind breastfeeding and childhood obesity, we assessed the association of weight gain with the mode of milk delivery aside from the type of milk given to infants.
Design: A longitudinal study of infants followed up from birth to age 1 year. Multilevel analyses were conducted to estimate infant weight gain by type of milk and feeding mode.
Setting: Pregnant women were recruited from a consumer mail panel throughout the United States between May 2005 and June 2007.
Participants: One thousand eight hundred ninety nine infants with at least 3 weight measurements reported during the first year.
Main exposures: Six mutually exclusive feeding categories and proportions of milk feedings given as breastmilk or by bottle.
Main outcome measures: Weight measurements reported on 3-, 5-, 7-, and 12-month surveys.
Results: Compared with infants fed at the breast, infants fed only by bottle gained 71 or 89 g more per month when fed nonhuman milk only (P < .001) or human milk only (P = .02), respectively. Weight gain was negatively associated with proportion of breastmilk feedings, but it was positively associated with proportion of bottle-feedings among those who received mostly breastmilk. Among infants fed only breastmilk, monthly weight gain increased from 729 g when few feedings were by bottle to 780 g when most feedings were by bottle.
Conclusions: Infant weight gain might be associated not only with type of milk consumed but also with mode of milk delivery. Regardless of milk type in the bottle, bottle-feeding might be distinct from feeding at the breast in its effect on infants' weight gain.