Although the potential protective effect of breastfeeding on obesity has been studies extensively, the causal role is still discussed. In a previous analysis of the Avon Longitudinal Study of Parents and Children (ALSPAC) conducted by Dr. John J. Reilly and colleagues, weight gain in the first 12 months was associated with an increased risk of obesity at 7 years also after adjustment for a wide range of potential confounding factors, whereas an apparent protective effect of breastfeeding was reversed after adjustment (BMJ 2005).

It has been suggested that the observed association between longer duration of breastfeeding and lower risk of obesity might be explained by reverse causality. The concern is that more rapid weight gain in infancy induces breastfeeding cessation, and that the faster weight gain itself entrains later obesity. Only few studies have had sufficient data to model this bidirectional relationship and they show heterogeneous results. We propose to model the relation between weight and breastfeeding in infancy and the joint effect on obesity with relevant statistical methods, namely the g-computation formula that can account for the proposed bidirectional relation between infant weight gain and breastfeeding.

The research questions of this proposal are:

1) To investigate whether infant weight and weight gain predicts subsequent infant feeding.

2) To investigate the joint effect of patterns of infant weight gain and breastfeeding on body mass index and risk of obesity through childhood

Exposure: infant feeding at several occasions (breastfeeding, bottle feeding and complementary feeding)

Outcomes: child anthropometrics from birth through childhood

Covariates: maternal education, paternal education, family income, occupational social class, maternal age at childbirth, parity, maternal size, maternal smoking, sex of the child and gestational age.