4.2 Study Protocol 4.2.1 Recruitment: Rolling recruitment over 1 year with 1-year follow up for all beginning in September of 2006 and continuing through August 2007. Equal numbers across all months will be sought. At least two large pediatric clinics (Médicentre St-Lazare and Clinique de santé jeunesse) will be the primary recruitment centres with over 1500 newborns annually receive their ongoing medical care. These clinics provide care to families with a wide range of SES and cultures representative of Montreal and Canada. Infants will be recruited at the first postnatal visit at 2 weeks of age. Such recruitment age is suitable since breastfeeding will be deemed as established and recovery of birth weight and good health are confirmed. The clinician will inform women and families who meet inclusion criteria, and only those who are interested in participating in the study will have their names and contact address and telephone number forwarded to the study coordinator. All study visits will take place at the Mary Emily Clinical Nutrition Research Unit, School of Dietetics and Human Nutrition.