Sites were randomly assigned an experimental intervention to promote longer duration and exclusivity of breastfeeding in mothers who initiated breastfeeding ( n = 16 sites ) , or a control intervention of continuing usual care ( n = 15 sites ) ; 17 046 healthy infants were enrolled in 1996-7 , of whom 13 751 ( 80.7 % ) completed the Children 's Eating Attitude Test ( ChEAT ) at 11.5 years of age .